Category: CBSE Class 10

Chapter 1 Chemical Reactions and Equations Class 10 Science Important Questions and Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Chemical Reactions and Equations Class 10 Important Questions and Answers Science Chapter 1

Very Short Answer Questions

Question 1.
Why does not a wall immediately acquire a white colour when a coating of slaked lime is applied on it ?
Answer:
Slaked lime as such is not very white. When applied on the wall, CO₂ gas present in air reacts with calcium hydroxide to form calcium carbonate. It is quite white and therefore, imparts white look to the wall.
Ca(OH)₂ + CO₂(g) ———> CaCO₃(s) + H₂O(l).

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
What is rust ?
Answer:
It is a brown mass known as hydrated ferric oxide. Its formula is Fe₂O₃.xH₂O.

Question 3.
Identify the most reactive and least reactive metal : Al, K, Ca, Au.
Answer:
Most reactive metal : K (potassium) ; Least reactive metal : Au (gold).

Question 4.
Which of the following is a combination reaction and which is a displacement reaction ?
(a) Cl₂ + 2KI ——–> 2KCl + I₂
(b) 2K + Cl₂ ——–> 2KCl.
Answer:
(a) It is a displacement reaction,
(b) It is a combination reaction.

Question 5.
What is the difference between the following two reactions ?
(a) Mg + 2HCl ——–> MgCl₂ + H₂
(b) NaOH + HCl ——–> NaCl + H₂O.
Answer:
(a) It is a single displacement reaction,
(b) It is a double displacement reaction also called neutralisation reaction.

Question 6.
Identify the compound which is oxidised in the following reaction
H₂S + Br₂ ———–> 2HBr + S.
Answer:
H₂S is oxidised to S because H₂S has lost hydrogen.

Question 7.
Suggest two ways to check the rancidity of food articles.
Answer:
(a) Keep the articles in airtight containers,
(b) Keep the articles in refrigerator.

Question 8.
Name two metals which donot get corroded.
Answer:
Gold (Au) and platinum (Pt) do not get corroded.

Question 9.
Identify the substance oxidised and reduced in the reaction :
CuO(s) + Zn(s) ———-> ZnO(s) + Cu(s).
Answer:
Zinc is oxidised to zinc oxide and copper oxide is reduced to copper.

Question 10.
How will you know whether a sample of cheese has become rancid or not ?
Answer:
If the cheese starts giving foul smell, it means that it has become rancid.

Question 11.
Why are eatables preferably packed in aluminium foils ?
Answer:
Aluminium foils donot corrode in atmosphere even if kept for a long time. Actually, a protective coating of aluminium oxide (Al₂O₃) is formed on the surface of the metal. It stops any further reaction of the metal with air (oxygen) and water. The eatables do not get spoiled.

Question 12.
What happens chemically when quick lime is added to water ?
Answer:
Calcium hydroxide (or slaked lime) is formed accompanied by a hissing sound. So much heat is evolved during the reaction that the reaction mixture starts boiling. The chemical equation for the reaction is :

Question 13.
Give an example of exothermic reaction.
Answer:
CH₄(g) + 2CO₂(g) ———-> CO₂(g) + 2H₂O(g) + heat, (evolved)

Question 14.
Give an example of endothermic reaction.
Answer:
N₂(g) + O₂(g) ———> 2NO(g) – heat, (absorbed).

Question 15.
Name the gas that can be used for the storage of fresh sample of chips for a long time.
Answer:
The gas is nitrogen (N₂). It checks rancidity of food articles.

Question 16.
Name the type of reaction
N₂(g) + 3H₂(g) ———-> 2NH₃(g)
Answer:
It is an example of combination reaction.

Question 17.
Give an example of a double displacement reaction (only reaction with complete balanced equation).
Answer:
HCl(aq) + NaOH(g) ——–> NaCl(aq) + H₂O(l)

Question 18.
Why are decomposition reactions called the opposite of combination reactions ? Write equations for these reactions.
Answer:
A decomposition reaction may be defined as the reaction in which a single substance decomposes or splits into two or more substances under suitable conditions.
For example,

It may be concluded that a certain substance is formed or synthesised in combination reaction and it breaks or splits in decomposition reaction. Therefore, the two reactions oppose each other.

Question 19.
In the reaction MnO₂ + 4HCl —————> MnCl₂ + 2H₂O + Cl₂; identify which one is reduced and which one is oxidized ?
Answer:
In this reaction HCl is oxidised to Cl₂ and MnO₂ is reduced to MnCl₂.

Question 20.
Take a small amount of calcium oxide or quick lime in a beaker and slowly add water to this. Is there any change in temperature ?
Answer:
Yes, the temperature increases since the process of dissolution of calcium oxide (CaO) in water is highly exothermic in nature.

Question 21.
Name two salts that are used in black and white photography.
Answer:
Both silver chloride and silver bromide are used in black and white photography.

Question 22.
State the chemical change that takes place when lime stone is heated
Answer:
Calcium carbonate decomposes on heating to give calcium oxide and carbon dioxide.
CaCO₃(s) heat , CaO(s) + CO₂(g)

Short Answer Questions

Question 23.
Identify the substance oxidised and substance reduced in the following reactions
(i) ZnO(s) + C(s) ———> Zn(s) + CO(g)
(ii) 2Na(s) + O₂(g) ———> 2Na₂O(s)
(iii) CuO(s) + H 2(g) ———> Cu(s) + H₂O(l).
Answer:
(i) C is oxidised to CO and ZnO is reduced to Zn.
(ii) Na is oxidised to Na₂O and O₂ is reduced.
(iii) H₂ is oxidised to H₂O and CuO is reduced to Cu.

Question 24.
Which types of reactions are represented by the following equations ?
(a) CaO + CO₂ ——-> CaCO₃
(b) Mg + CuSO₄ ——–> MgSO₄ + Cu
(c) CH4 + 2O₂ ———–> CO₂ + 2H₂O
(d) NH₄NO₂ ———-> N₂ + 2H₂O.
Answer:
(a) Combination reaction
(b) Displacement reaction
(c) Combustion reaction
(d) Decomposition reaction

Question 25.
What happens when :
CO₂(g) is bubbled through lime water (i) in small amount (ii) in excess
Answer:
(i) Solution becomes milky due to the formation of calcium carbonate

(ii) Milkiness disappears because calcium carbonate changes to calcium hydrogen carbonate which is colourless in nature.

Question 26.
Aluminium is a reactive metal but is still used for packing food articles. Why ?
Answer:
From the position of the aluminium (Al) metal in the activity series, it seems to be quite reactive. However, it is not so reactive. Actually, when the metal is kept in air or oxygen for sometime, it is converted into its oxide called aluminum oxide (Al₂O₃). This gets deposited as the surface of the metal as a thin coating. It is rather passive which means that it is not reactive. Therefore, the metal is used for packing food articles which do not get spoiled under the foil.

Question 27.
Give one example each of :
(i) Thermal decomposition reaction
(ii) Electrolytic decomposition reaction
(iii) Photo decomposition reaction. (CBSE 2014)
Answer:

Question 28.
What are neutralisation reactions ? Why are they so named ? Give one example.
Answer:
A neutralisation reaction is a chemical reaction between an acid and base dissolved in water. For example,
KOH(aq) + HNO₃(aq) ———-> KNO₃(aq) + H₂O (aq)
It is called neutralisation as both KN03 (salt) and H20 that are formed as the products, are of neutral nature.

Question 29.
(a) Why is combustion reaction an oxidation reaction ?
(b) How will you test whether the gas evolved in a reaction is hydrogen ?
(c) Why does not silver evolve hydrogen on reacting with dillute sulphuric acid ?
Answer:
(a) Combustion reaction is an oxidation reaction because it is always carried in the presence of air or oxygen. For example,
CH₄(s) + 2O₂(g) ——–> CO₂(g) + 2H₂O (l)
(b) Bring a burning match stick close to the mouth of the tube from which hydrogen gas escapes. The gas will immediately catch fire and this will be accompanied by pop sound.
(c) Silver is a less reactive metal in the sense that it occupies a place below hydrogen in the reactivity series. Therefore it does not evolve hydrogen gas on reacting with either dilute sulphuric acid or dilute hydrochloric acid.

Question 30.
What is an oxidation reaction ? Identify in the following reactions :
(i) the substance oxidised
(ii) the substance reduced.
Answer:
ZnO + C ———> Zn + CO
Oxidation involves the addition of oxygen or the removal of hydrogen in a chemical reaction. In the given reaction, carbon is oxidised to carbon monoxide while zinc oxide is reduced to zinc.

Question 31.
Identify the type of reaction in the following examples :
(i) Na₂SO₄(aq) + BaCl₂(aq) ———-> BaSO₄(s) + 2NaCl(aq)
(ii) Fe(s) + CuSO₄(aq) ———-> FeSO₄(aq) + Cu(s)
(iii) 2H₂(g) + O₂(g) ———> 2H₂O(l)

Answer:
(i) It is an example of double displacement reaction.
(ii) It is an example of displacement reaction.
(iii) It is an example of combination reaction.

Question 32.
Solid calcium oxide was taken in a container and water was added slowly to
(i) State two observations made in the experiment.
(ii) Write the name of the chemical formula of the product.
Answer:
(i) Water will start boiling and hissing noise will be produced.
(ii) Calcium hydroxide (slaked lime) will be formed.

Question 33.
A house wife wanted her house to be white washed. She bought 10 kg of quick lime from the market and dissolved in 30 litres of water.

Answer:
She noticed that water started boiling even when it was not being heated. Give reason for her observation. Write the corresponding equation and name the product formed.
A suspension of slaked lime also called calcium hydroxide is formed when water is added to quick lime.

Since the reaction is highly exothermic, the solution started boiling although it was not being heated. The suspension of slaked lime is allowed to cool for sometime, preferably overnight. It is then decanted and the liquid obtained is used for white washing.

Question 34.
(i) What is observed when a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube ?
(ii) What type of reaction is this ?
(iii)Write a balanced equation to represent the above reaction.
Answer:
(i) A yellow precipitate of lead iodide appears at the bottom of the test tube.
(ii) It is an example of double displacement reaction.
(iii) The balanced equation for the reaction is :

Question 35.
What change in colour is observed when white silver chloride is left exposed to sun light ? State the type of chemical reaction in this change.
Answer:
White colour of silver chloride changes to grey due to formation of metallic silver. The reaction is known as photochemical reaction. It is also a decomposition reaction.

Question 36.
What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride ? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction. (CBSE 2016)
Answer:
A white precipitate of barium sulphate is immediately formed when the two aqueous solutions are mixed in a test tube. No reaction will be possible if the two reactants are in the solid state. The balanced chemical equation for the double displacement reaction is :

Question 37.
What is a redox reaction ? When a magnesium ribon burns in air with a dazzling flame and forms a white ash; is magnesium oxidised or reduced ? Why ?
Answer:
A redox reaction is a chemical reaction in which one of the reactants gets oxidised while the other is reduced simultaneously. In the reaction under study, magnesium is oxidised to magnesium oxide since the metal has gained oxygen.

Question 38.
(a) What happens chemically when quick lime is added to water ? (CBSE 2012)
(b) Write the chemical equation in balanced form.
MnO₂ + HCl ———-> MnCl₂ + Cl₂ + H₂O
(c) What is decomposition reaction ? Explain it with suitable example.
Answer:
(a) When quick lime (CaO) is added to water, slaked lime Ca(OH)₂ is formed. The reaction is highly exothermic in nature.
(b) The balanced chemical equation is :
MnO₂ + 4HCl ———-> MnCl₂ + 2H₂O + 2Cl₂.
(c) Decomposition reaction is a chemical reaction in which a single substance splits or breaks into two or more substances under suitable conditions. For example,

Long Answer Questions

Question 39.
(a) Why cannot a chemical change be normally reversed ?
(b) Why is it always essential to balance a chemical equation ?
(c) Why do diamond and graphite, the two allotropie forms of carbon evolve different amounts of heats on combustion ?
(d) Can rusting of iron take place in distilled water ?
Answer:
(a) In a chemical change, the products are quite different from the reactants. Therefore, it cannot be normally reversed.
(b) A chemical equation has to be balanced to meet the requirement of the law of conservation of mass. According to the law, the total mass of the reacting species taking part in the reaction is the same as that of the products formed. Since there is a direct relationship between the mass of the different species and their number, it is always essential to balance a chemical equation.
(c) Because they differ in the arrangement of carbon atoms present and have different shapes. The attractive forces among the atoms in the two cases are not same. That is why they evolve different amount of heat.
C(diamond) + O₂(g) ———–> CO₂(g) + 393.5 kj
C(graphite) + O₂(g) ———–> CO₂(g) + 395.4 kj
Please note that diamond and graphite are the two allotropie forms of carbon.
(d) No, rusting of iron cannot take place in distilled water because it neither contains dissolved oxygen nor carbon dioxide. Both are essential for the rusting of iron.

Question 40.
You are given the following materials :
(i) Iron nails
(ii) Copper sulphate solution
(iii) Barium chloride solution
(iv) Copper powder
(v) Ferrous sulphate crystals
(vi) Quick lime.
Identify the type of chemical reaction taking place when :
(a) Barium chloride solution is mixed with copper sulphate solution and a white precipitate is observed.
(b) On heating, copper powder in air in a china dish, the surface of copper powder becomes black.
(c) On heating green ferrous sulphate crystals, reddish brown solid is left and a gas having smell of burning sulphur is noticed.
(d) Iron nails when left dipped in blue copper sulphate solution become brownish in colour and blue colour of copper sulphate solution fades away.
(e) Quick lime reacts vigorously with water releasing a large amount of heat.
Answer:
(a) The reaction is double displacement in nature. ‘

(b) It is an example of combination reaction.

(c) The green crystals of ferrous sulphate have the chemical formula FeS04.7H20. Upon heating, they lose molecules of water of crystallisation.

Upon further heating, ferrous sulphate undergoes decomposition reaction as follows :

Both the gases evolved have the smell of burning sulphur.
(d) This happens because of displacement reaction. Iron displaces copper form copper sulphate solution. Brownish coating of copper gets deposited on the iron nails. As the concentration of copper sulphate in the solution decreases, the blue colour of the solution slowly fades.

(e) Calcium hydroxide is formed as a result of combination reaction. It is highly exothermic. A large amount of heat is evolved accompanied by hissing sound.

Question 41.
A silvery white metal X is in the form of ribbons. Upon ignition, it burns with a dazzling white flame to form white powder Y. When water is added to the powder Y, it partially dissolves to form a substance Z which is used as an antacid.
(a) What is metal X ?
(b) Name the white powder Y.
(c) What is the substance Z ?
(d) Write the chemical reactions that are taking place.
Answer:
(a) The metal is X is Mg.
(b) The white powder Y is MgO.
(c) White powder Y dissolves partially in water to form substance Z. It is Mg(OH), and is used as an antacid.
(d) The chemical reactions that are taking place are :

Question 42.
(i) Account for the following :
(a) White silver chloride turns grey in sunlight.
(b) Brown coloured copper powder on heating in air turns into black coloured substance.
(ii) What do you mean by
(a) Displacement reaction
(b) Reduction reaction
(c) Combination reaction ? Write balanced chemical equation.
Answer:
(i) (a) White coloured silver chloride undergoes decomposition in the presence of sunlight and forms silver (grey in colour) and chlorine.

(b) Brown coloured copper powder on heating in air gets oxidised to copper oxide which is black in colour.

(ii) For the different types of reactions,
(a) In a displacement reaction, one element takes the place of another in a compound dissolved in a solution. For example,
Fe(s) + CuSO₄ (aq) ———> FeSO₄ (aq) + Cu(s)
(b) Combination reaction may be defined as the reaction in which two or more substances combine under suitable conditions to form a new substance. For example,

(c) A decomposition reaction may be defined as the reaction in which a single substance decomposes or splits into two or more substances under suitable conditions.
For example,

It may be concluded that a certain substance is formed or synthesised in combination reaction and it breaks or splits in decomposition reaction. Therefore, the two reactions oppose each other.

Question 43.
(a) Write the chemical equation in the balanced form.
Fe(s) + H₂O(g) ———–> Fe₃O₄(s) + H₂(g)
(b) Identify the type of reaction from the equation given below :
Na₂SO₄ (aq) + BaCl₂ (aq) ———–> BaSO₄(s) + NaCl(aq)
(c) You could have noted that when copper powder is heated in a china dish, the surface of copper powder gets coated with black coloured substance.
(i) Why is this black coloured substance formed ?
(ii) What is this black substance ?
(iii) Write the chemical equation of the reaction taking place.
Answer:
(a) 3Fe(s) + 4H₂O(g) ————> Fe₃O₄(s) + 4H₂(g)
(b) It is a double displacement reaction also called precipitation reaction. A white precipitate of BaSO₄ is formed in the reaction.
(c)
(i) The black substance is formed due to the oxidation of copper.
(ii) The black substance is cupric oxide or copper (II) oxide with formula CuO.

Question 44.
Observe the given figure and answer the following questions.

(a) Write the complete balanced reaction for the reaction that takes place.
(b) Type of reaction involved.
(c) Is there any precipitate formed.
(d) If any precipitate formed, write the colour of the precipitate.
Answer:

(b) It is a double displacement reaction
(c) Yes, a precipitate of barium sulphate is formed.
(d) The precipitate is white in colour.

Question 45.
Select (i) combination reactions (ii) decomposition reactions and displacement reactions from the following

Answer:
(i) Decomposition reaction
(ii) Displacement reaction
(iii) Combination reaction
(iv) Displacement reaction
(v) Combination reaction
(vi) Decomposition reaction.

Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 1 Chemical Reactions and Equations are helpful to complete your science homework.

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Chapter 8 How do Organisms Reproduce Class 10 Science Important Questions with Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

How do Organisms Reproduce Class 10 Important Questions and Answers Science Chapter 8

Very Short Answer Questions

Question 1.
Write the full expansion of HIV.
Answer:
Human immuno-deficiency virus.

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
Write the full form of IUCD.
Answer:
Intra-uterine contraceptive device.

Question 3.
Name the type of fission carried out by Amoeba.
Answer:
Binary fission.

Question 4.
What is vegetative propagation ? (CBSE Delhi 2006 C)
Answer:
It is the formation of new plants from vegetative parts (e.g., stem, leaf, root, bud) of a parent plant.

Question 5.
List two functions performed by ovaries in a human female. (CBSE A.I. 2006 C)
Answer:

1. Formation of ova
2. Secretion of hormones, estrogen and progesterone.

Question 6.
What is the effect of DNA copying which is not perfectly accurate in the reproductive process ?.
(CBSE A.I. 2008)
Answer:
It produces mutations which give rise to useful, harmful and neutral variations in the progeny.

Question 7.
Name the hormone, secretion of which is, responsible for dramatic changes in appearance in girls when they approach 10-12 years of age.
Answer:
Estrogen (= oestrogen) produced by growing follicles inside the ovary.

Question 8.
Why is DNA copying an essential part of the process of reproduction ?
Answer:
Cell multiplication is essential for reproduction either as a means of multiplication in unicellular organisms or as a means of development of multicellular body from a single celled zygote. Cell multiplication cannot occur without DNA replication or DNA copying because each new cell must carry the full DNA complement.

Question 9.
Mention the common mode of reproduction found in

1. Amoeba
2. Planaria.

Amoeba Binary fission in any plane.

Answer:
Planaria: Transverse binary fission.

Question 10.
Name any two types of asexual reproduction.
Answer:
Fission, Spore formation.

Question 11.
State the method used for growing rose plants.
Answer:
Artificial method of vegetative propagation by stem cuttings and bud grafting.

Question 12.
State what type of method is used for growing jasmine plant.
Answer:
Layering, a type of artificial method of vegetative propagation.

Question 13.
No two individuals are absolutely alike in a population. Why ?
Answer:
Due to presence of variations.

Question 14.
“Cell division is a type of reproduction in unicellular organisms”. Justify. (CCE 2013)
Answer:
In unicellular organisms cell division is a mode of reproduction as it produces two individuals or daughters by division of the parent cell.

Question 15.
Name the type of reproduction which
(a) involves gametes
(b) Does not involve gametes. (CCE 2013)
Answer:
(a) Sexual reproduction
(b) Asexual reproduction.

Question 16.
Define puberty. (CCE 2014)
Answer:
It is the beginning of development for sexual maturity which occurs at the age of 10-14 years in girls and 13—15 years in boys. Fully formed primary sex organs start secreting hormones for slow development of secondary sex organs and secondary sex characters.

Question 17.
Name the life process of an organism that helps in the growth of its population. (CCE 2015)
Answer:
Reproduction.

Question 18.
Name two simple organisms having the ability of regeneration. (CCE 2015)
Answer:
Hydra, Planaria.

Question 19.
Where is DNA found in the cell ? (CCE 2015)
Answer:
Nucleus, plastids and mitochondria.

Question 20.
Name the type of reproduction mostly seen in unicellular organisms. (CCE 2015)
Answer:
Asexual reproduction through cell division as binary fission, multiple fission, sporulation, budding.

Question 21.
Define sexual reproduction. (CCE 2015)
Answer:
It is a mode of reproduction in which offspring are formed by the process of formation and fusion of gametes.

Question 22.
In human female reproductive system where does fertilization occur ?
Answer:
In fallopian tube at ampulla—isthmus junction.

Question 23.
Name the parts where germ cells of a flower are located.
Answer:
Male — in anther of stamen.
Female — in ovule of carpel.

Question 24.
Name the part of Bryophyllum where buds are produced for propagation.
Answer:
Leaf notches.

Question 25.
What is DNA ?
Answer:
DNA or deoxyribonucleic acid is a self replicating biochemical that is carrier of genetic information for expression of hereditary traits and transfer to the next generation.

Question 26.
What happens when a planaria gets cut into two pieces ?
Answer:
Each piece grows (regenerates the missing parts) to form a complete animal.

Question 27.
Name the method by which Hydra reproduces commonly. Is this method sexual or asexual ?
(CBSE Foreign 2016)
Answer:
Hydra reproduces commonly by budding (also regeneration). It is a method of asexual reproduction.

Question 28.
List two unisexual flowers. (CBSE Foreign 2016)
Answer:
Water Melon, Papaya.

Question 29.
Why is fertilization not possible without pollinatign ? (CBSE Foreign 2016)
Answer:
Fertilization requires bringing of male gametes to the female gamete which is possible only when pollen grain is brought from the anther to the stigma in the process of pollination.

Question 30.
What happens when a mature Spirogyra filament attains considerable length ? (CBSE A.I. 2016)
Answer:
The elongated mature filament of Spirogyra breaks to form smaller pieces or fragments. The fragments grow to form mature filaments. .

Question 31.
What are those organisms called which bear both the sex organs in the same individual ? Give one example of such organism. (CBSE A.I. 2016)
Answer:
Bisexual or hermaphrodite, eg., Mustard, Hydra.

Question 32.
List two functions of ovary of human female reproductive system. (CBSE A. I. 2016)
Answer:

1. Formation of ova
2. Secretion of hormones estrogen and progesterone.

Question 33.
Name the method by which Spirogyra reproduces under favourable conditions. Is this method sexual or asexual ?
(CBSE Delhi 2017)
Answer:

1. Fragmentation
2. Asexual method.

Question 34.
Flow does Planaria reproduce ? Is this method sexual or asexual ? (CBSE Delhi 2017)
Answer:

1. Transverse binary fission and regeneration
2. Asexual method.

Question 35.
How does Plasmodium reproduce ? Is this method sexual or asexual ? (CBSE A.I. 2017)
Answer:

1. Multiple fission,
2. Asexual method.

Question 36.
When a cell reproduces, what happens to its DNA ? (CBSE A.I. 2017)
Answer:
DNA replicates and forms its copy at the time of cell reproduction.

Question 37.
Newly formed DNA copies may not be identical at times. Give one reason. (CBSE A.I. 2017)
Answer:
Error in DNA copying due to incorporation of wrong nucleotide.

Question 38.
Why is variation important for a species ? (CBSE A.I. 2017)
Answer:
Variation provides adaptability to changing environment and increased fitness in the struggle for existence.

Question 39.
Name the organs producing
(i) male germ cells / sperms and
(ii) female germ cells / ova respectively in humans. (CBSE Foreign 2017)
Answer:
(i) Testis
(ii) Ovary.

Question 40.
What is fertilisation ? Where does it occur in a human female ? (CBSE Foreign 2017)
Answer:
Fertilisation is the fusion of male and female gametes to form diploid zygote. In human female, it occurs in ampulla part of fallopian tube.

Short Answer Questions (2 Marks Each)

Question 1.
List any two differences between pollination and fertilization. (CBSE Delhi 2008, 2009, 2010)
Answer:

Pollination	Fertilization
1.    Definition. It is transfer of pollen grains from anther to the stigma of a flower. 2.    Step. Pollination precedes fertilization. 3.    Purpose. It carries the male gamete producing pollen grains to the female sex organ. 4.  Process. Pollination is a physical process. 5. Occurrence. It occurs only in seed plants.	It is the fusion of male and female gametes. Fertilization occurs only after pollination when the pollen grain has germinated and male gametes are carried into ovule. It actually brings about fusion of gametes. Fertilization is a physico-chemical (biological) process. It occurs in both plants and animals of various types.

Question 2.
What is reproduction ? Mention the importance of DNA copying in reproduction. (CBSE Delhi 2008)
Answer:
Definition: Reproduction is the process of producing new young individuals of similar type by the mature individuals.
Importance of DNA Copying.
DNA carries hereditary information not only for controlling cellular functions but also all the structural and functional traits of organism. It is because of the latter that single celled zygote is able to form the whole multicellular organism. During reproduction there is formation of new cells which must carry the same amount and type of hereditary information as present in the parent cell. This is accomplished by DNA copying, which occurs prior to each cell division. DNA copying is not error proof. Errors give rise to variations.

Question 3.
Define variations in relation to a species. Why is variation beneficial to the species ? (CBSE Delhi 2008, CCE 2013)
Answer:
Definition: Variation is differences in structure, physiology and other characters found in the individuals of the same organism.
Benefits of variations to species.
Many of the variations are pre-adaptations which have no immediate benefit to the individuals. However, they remain in the population. Whenever, environment undergoes a drastic change, the pre-adaptations present in some members of the population allow the latter to survive, grow and regain its former size. Therefore, it is not necessary that variations are beneficial to individuals developing them but can prove useful to the species.

Question 4.
Mention the information source of making proteins in the cell. What is the basic event in reproduction ?
(CBSE Delhi 2008, 2009 C)
Answer:
Information Source: The information source of making proteins in a cell is its DNA.
Basic Event in Reproduction: The basic event in reproduction is replication of DNA, growth of cellular machinery and cell division.

Question 5.
Name one sexually transmitted disease each caused by a bacterial infection and viral infection. How can they be prevented ? (CBSE A.I. 2008, CCE 2012)
Answer:
Bacterial STD. Gonorrhoea caused by Neisseria gonorrhoeae. Viral STD. Genital warts caused by Human Papilloma virus.
Prevention. Avoiding multipartner sex, use of condoms and clean toilet habits.

Question 6.
(a) In human body what is the role of

1. seminal vesicles and
2. prostate gland.

(b) List two functions performed by testes in human beings. (CBSE A.I. 2008, 2009, CCE 2013)
Answer:
(a)

1. Seminal Vesicles: They secrete 60-70% of semen plasma that is alkaline and viscous having fructose (for nourishing the sperms), fibrinogen, proteins and prostaglandins. Prostaglandins cause movements in the genital tract of the female. Sperms are also activated by secretion of seminal vesicles.
2. Prostate Gland: It produces 20-30% of semen plasma. The secretion is alkaline and viscous. It has clotting enzyme and chemical essential for sperm activity.

(b) Function of Testes,

1. Formation of sperms from germinal cells of seminiferous tubules.
2. Secretion of testosterone by Leydig cells present in the connective tissue in between the seminiferous tubules.

Question 7.
Name the male and female gametes in animals. What is fertilization and where does it take place in human females ? (CBSE Delhi 2009)
Answer:
Male Gamete: Sperm (= spermatozoan)
Female Gamete: Ovum.
Fertilization: It is the fusion of two compatible gametes (e.g., sperm and ovum) to form diploid zygote during sexual reproduction.
In human females fertilization occurs in fallopian tube.

Question 8.
What is reproduction ? What are the two types ? Which one of the two confers new characteristics on the offspring and how ? (CBSE A.I. 2009 C, 2017)
Answer:
Reproduction: Reproduction is the process of producing new young individuals of similar type by the mature individuals.
Importance of DNA Copying.
Types. Asexual reproduction and sexual reproduction.
New Characteristics: New characteristics appear only in sexual reproduction due to

1. Chance separation of chromosomes during meiosis required for gamete formation,
2. Crossing over during meiosis.
3. Chance coming together of chromosomes during fertilization,
4. Mutations or mistakes during DNA replication.

Question 9.
What is binary fission ? Draw a diagram to show binary fission in Amoeba. (CBSE A.I. 2009 C)
Answer:
Binary Fission. It is a mode of asexual reproduction in a mature individual which splits up or divides to form two individuals.

Question 10.
What is regeneration ? State a reason why a more complex organism cannot give rise to new individuals through this method. (CBSE A.I. 2009 C)
Answer:
Regeneration. It is ability of an individual to form lost or broken parts, sometimes the entire individual I from a piece of the parent body. The ability to form the whole individual from a piece of parent body is
found only in simple animals like Hydra and Planaria. It does not occur in complex organisms like humans, birds, lizards etc. Here regeneration is limited to repair or regeneration of minor parts. It is because the tissues and organs are highly differentiated in complex animals.

Question 11.
With the help of diagram, show the different stages of binary fission in Amoeba. (CBSE Delhi 2010)
Answer:

1. Pseudopodia shorten,
2. Nucleus elongates and divides into two.
3. The perent cleaves in between the two daughter nuclei to form two daughter individuals.

Question 12.
State in brief two junctions ofcopper-T used by some women. (CCE 2011)
Answer:

1. Destruction of sperms
2. Prevention of implantation.

Question 13.
(a) Give reason : Regeneration is not the same as reproduction.
(b) State the mode of asexual reproduction in Plasmodium. (CCE 2011)
Answer:
(a) Regeneration is not the same as reproduction as no propagule is formed and no organism will depend on being cut to be able to reproduce.
(b) Multiple fission.

Question 14.
How does Rhizopus multiply by spores. Explain in brief. Sketch neat labelled diagram of this method.
(CCE 2011)
Answer:
Spores of Rhizopus are nearly always present in the air. They settle down on moist organic matter like bread, germinate and form mycelia. A mycelium bears a number of black aerial blobs or sporangia wherein spores are | formed. The wall of sporangium breaks and the released spores are picked up by air for dispersal. Draw

Question 15.
(i) List two reproductive parts of a flower.
(ii) How is a unisexual flower different from a bisexual flower ? State in brief. (CCE 2011)
Answer:
(i) Male — Stamen.
Female — Carpel/Pistil
(ii) A unisexual flower possesses one types of reproductive organs, either stamens (staminate or male flower) or pistils (pistillate or female flower) while a bisexual flower has both the types of reproductive organs.

Question 16.
In what respect is the human male gamete different from the female gamate ? What is the importance of this difference ? (CCE 2011, 2014)
Answer:
Male gamete or sperm is smaller, dart-like motile gamete with scanty amount of food reserve. Female gamete or ovum is larger, rounded, non-motile gamete with a good amount of reserve food. The difference helps the ovum to get loaded with cytoplasmic contents and allow the sperm to swim freely upto the ovum.

Question 17.
What will happen when (a) A mature Spirogyra filament attains considerable length
(b) Planaria gets cut into two pieces ? (CCE 2011)
Answer:
(a) Spirogyra genrally undergoes fragmentation with each fragment or smaller piece growing to form long ‘ filament.
(b) Each piece of Planaria regenerates or grows the missing parts to form the complete animal.

Question 18.
What are sexually transmitted diseases ? Name an STD which damages the immune system of human body.
(CCE 2011)
Answer:
Sexually transmitted diseases (STDs) or venereal diseases (VDs) are infectious diseases that are transmitted by
sexual contact between a healthy person and an infected person. STD that damages the immune system is HIV-AIDS.

Question 19.
(a) Surgical methods can be used to create a block in the reproductive system for contraceptive purposes. Name such parts where blocks are created in

1. Males
2. Females.

(b) State any two reasons for using contraceptive devices. (CCE 2011)
Answer:
(a)

1. Vasa deferentia
2. Fallopian tubes.

(b) Contraceptive devices are used to prevent pregnancy for

1. Limiting size of family by spacing birth of children
2. Avoiding unwanted pregnancy.

Question 20.
What is vegetative propagation ? Write two of its advantages. (CCE 2011, 2012, 2013, 2014)
Answer:
Vegetative propagation is the formation of new plants by using vegetative parts of a parent plant as propagules e.g., stem (Sugarcane, Bougainvillea, Potato), root (Sweet Potato, Dahlia), leaf (Bryophyllum), bud (Agave).
Advantages:

1. It is the only known method of multiplication of seedless plants like Banana and Sugarcane.
2. It is a quicker method as vegetatively reproduced plants bear flowers and fruits earlier than plants raised through seeds.
3. All the individual plants are clones of one another and their parent so that the crop is genetically uniform.
4. Good quality of a variety can be maintained indefinitely.

Question 21.
Name the type of asexual reproduction in
(a) Planaria
(b) Rhizopus
(c) Spirogyra
(d) Hydra. (CCE 2011)
Answer:
(a) Planaria —regeneration,
(b) Rhizopus — spore formation
(c) Spirogyra — fragmentation
(d) Hydra — budding.

Question 22.
Differentiate between
(a) Asexual reproduction and sexual reproduction
(b) Self pollination and cross pollination.
(CCE 2011, 2012)
Answer:
(a) Asexual reproduction is monoparental, with no gametes, no meiosis and very little variations. Sexual reproduction is generally biparental involving fusion of gametes, meiosis and lot of variations.
(b) Self pollination is transfer of pollen grains from the anther to the stigma of the same flower (e.g., Commeliria, Wheat) while cross pollination is transfer of pollen grains from the anther of one flower to the stigma of another flower of the same species (e.g., Salvia).

Question 23.
State two points of importance of DNA copying in reproduction. (CCE 2011, 2012)
Answer:

1. Copying of DNA during reproduction provides the same and full complement of DNA to each and every cell which is important because DNA controls not only cellular functions but also structural and functional traits of the individual.
2. Copying of DNA is not one hundred percent fool proof. Some variations develop due to small errors in copying.

Question 24.
How does the process of budding differ from the process of spore formation ? (CCE 2011)
Answer:

Budding	Spore Formation
1.      Number: One or a few buds develop over the body of an individual. 2.      Dispersal: It is limited. 3.      New Individual: The bud directly grows into a new individual. Ex. Hydra.	A very large number of spores develop from an individual. Spores are dispersed far and wide. A spore germinates and then forms a new individual. Ex. Rhizopus.

Question 25.
(a) Out of the following plants, which two plants reproduce by vegetative propagation : Jasmine, Wheat, Mustard, Banana ?
(b) List any one advantage of practising this kind of propagation. (CCE 2011)
Answer:
(a) Jasmine (layering), Banana (cutting of rhizome).
(b) Advantages:

1. It is the only known method of multiplication of seedless plants like Banana and Sugarcane.
2. It is a quicker method as vegetatively reproduced plants bear flowers and fruits earlier than plants raised through seeds.
3. All the individual plants are clones of one another and their parent so that the crop is genetically uniform.
4. Good quality of a variety can be maintained indefinitely.

Question 26.
Illustrate the process of regeneration in Planaria with help of a suitable diagram. (CCE 2011)
Answer:
On being cut or broken into two or more pieces, each piece grows to form the complete animal of Planaria. It is done with the help of

1. dedifferentiation of differentiated cells and
2. reserve cells which proliferate, reach the exposed parts and differentiate to form the missing regions.
   

Question 27.
Leaves of Bryophyllum fallen on the ground produce new plants. Why ? (CCE 2011)
Answer:
Leaves of Bryophyllum bear adventitious buds in thè marginal notches. As the leaves fall down on the ground and come in contact with soil, the buds sprout and form new plants.

Question 28.
State the significance of human testes being located in the scrotum. (CCE 2011, 2012)
Answer:

1. Scrotum not only protects the testes but also acts as a thermoregulator by changing position of the testes.
2. It keeps the temperature of testes 1 -3° C below that of the body. A lower temperature is essential for development of sperms.

Question 29.
(a) What will happen to ovary and ovule after fertilization in angiospermic plants ?
(b) Name two animals that reproduce asexually.
(c) What are the male and female gonads in human beings known as ? (CCE 2011)
Answer:
(a) Ovary — fruit.
Ovule — seed.
(b) Hydra, Sponges
(c) Male Gonads —Testes.
Female Gonads-Ovaries.

Question 30.
Protozoans reproduce by binary fission as well as multiple fission. In your opinion which process is better and why ? (CCE 2011)
Answer:
Multiple fission is better as

1. it often occurs inside perennating cysts
2. it produces many daughters.

Question 31.
In Tobacco plant, the male gametes have 24 chromosomes. State the number of chromosomes in

1. Egg nucleus
2. Zygote
3. Endosperm
4. Leaf cell. (CCE 2011)

Answer:

1. 24
2. 48
3. 72
4. 48.

Question 32.
The organisms formed by asexual reproduction are considered as clones Why ? State the advantage of sexual reproduction over asexual reproduction. (CCE 2011)
Answer:
Organisms formed through asexual reproduction are considered clones as they are genetically similar to one another as well as their parent.
Sexual reproduction is advantageous over asexual reproduction as it produces a lot of variations due to reshuffling of chromosomes and crossing over. This provides better adaptability, more vigour and vitality to the offspring.

Question 33.
(a) What is the site of implantation and development of young one in human female ?
(b) Mention two advantages of using mechanical barriers during sexual act. (CCE 2011)
Answer:
(a) Uterus,
(b)

1. Non-transmission of STDs
2. Prevention of pregnancy.

Question 34.
(a) Leaves of Bryophyllum fallen on ground produce new plants whereas the leaves of Jasmine do not. Why ?
(b) Write two points of differences between asexual and sexual reproduction. (CCE 2011, 2012)
Answer:
(a) Leaves of Bryophyllum possess adventitious buds in their marginal notches. The buds sprout to produce plantlets when leaves fall on soil. Leaves of Jasmine cannot undertake asexual reproduction as they do not develop adventitious buds.
(b)

Asexual Reproduction	Sexual Reproduction
1. Parents: It is monoparental.	It is generally biparental
2. Meiosis: Meiosis does not occur during asexual reproduction. There are no gametes and no fertilization.	Meiosis occurs: Gametes are formed and fertilization occurs in sexual reproduction.
Ex: Binary fission in Amoeba, Budding in Yeast	Ex: Offspring in Wheat, Human.

Question 35.
(a) Name the parts of the flower which ripens to form fruit and seed

(b) In the diagram, label A and B.
(CCE 2011)
Answer:
(a) Fruit — Ovary.
Seed — Ovule.
(b) A — plumule.
B — radicle.

Question 36.
With the help of a diagram only show regeneration in Planaria. Regeneration is not possible in all types of animals. Why ? (CCE 2011)
Answer:

1. Regeneration is possible in only simple animals having reserve or stem cells.
2. In complex higher animals regeneration is controlled by nervous and hormonal systems which become impaired at the site of injury.

Question 37.
How does the process of seed germination take place in plants ? Describe in brief. (CCE 2011)
Answer:
Seed germination occurs when a seed is placed in moist soil in such a way that it is also able to absorb oxygen from air. The seed absorbs moisture through its micropyle. The embryo becomes active. The seed coat softens. Seed interior swells causing breaking of seed coat. The radicle grows, passes out of the seed and enters the soil as root. The plumule, with or without cotyledons, comes out of soil and gives rise to shoot. The seedling becomes nutritionally independent.

Question 38.
Name the sex hormones secreted by male and female sex organs in human beings. State one function of each.
(CCE 2011)
Answer:
Male — Testosterone — Sperm formation and male characteristics.
Female —

1. Estrogen — Release of ovum, maintenance of female characteristics,
2. Progestérones— development of uterine lining.

Question 39.
(a) How is the process of pollination different from fertilization ?
(b) State the mode of reproduction in Earthworm, Frog, Rhizopus and Plasmodium (CCE 2011)
Answer:
(a)

Pollination	Fertilization
1.    Definition. It is transfer of pollen grains from anther to the stigma of a flower. 2.    Step. Pollination precedes fertilization. 3.    Purpose. It carries the male gamete producing pollen grains to the female sex organ. 4.  Process. Pollination is a physical process. 5. Occurrence. It occurs only in seed plants.	It is the fusion of male and female gametes. Fertilization occurs only after pollination when the pollen grain has germinated and male gametes are carried into ovule. It actually brings about fusion of gametes. Fertilization is a physico-chemical (biological) process. It occurs in both plants and animals of various types.

(b) Earthworm—sexual, also asexual.
Frog — sexual.
Rhizopus —spore formation, also sexual.
Plasmodium — multiple fission, also sexual.

Question 40.
Prenatal sex determination has been prohibited by law. State two reasons. (CCE 2011)
Answer:

1. The test has been banned since due to desire of male child, there has been large scale female foeticide.
2. This has resulted in declining female-male sex ratio.

Question 41.
What is placenta ? State its two roles during pregnancy. (CCE 2011)
Answer:
Placenta is a spongy vascular structure formed by the joint activity of maternal and foetal tissues in the wall of uterus that connects foetus with uterus.
Roles:

1. Providing nutrition to the foetus.
2. Taking away wastes of the foetus.

Question 42.
Compare the vegetative propagation of Bryophyllum and Money plant. (CCE 2011)
Answer:
In Bryophyllum, vegetative propagation occurs through the agency of leaves that fall on moist soil. In Money Plant, vegetative propagation occurs with the help of stem cuttings bearing at least one leaf and its axillary bud. A single leaf of Bryophyllum can produce several plants. A leafy stem cutting of Money Plant forms only a single plant.

Question 43.
(a) Where are the male germ cell and female gamete produced in a flower ?
(b) State the significance of variation in reproduction.
(c) Mention the principle of regeneration. (CCE 2011)
Answer:
(a) Male Germ Cell (Male Gamete). Formed inside the pollen tube or pollen grain from generative cell.
Female Gamete (Oosphere). Inside embryo sac part of ovule.
(b) Significance of Variation in Reproduction

1. It provides individuality to each living organism,
2. It helps individuals in the struggle for existence,
3. Variation is a source of preadaptation.

(c) Principle of Regeneration: It is the ability of an individual to form lost or broken part, sometimes the entire individual from a piece of the parent body through dedifferentiation of mature cells and activity of reserve cells. The ability to form a new individual from a part of the body is well developed in simple animals like Hydra and Planaria. It is restricted to the formation of only broken parts in complex organisms.

Question 44.
(a) Name two bacterial STD infections.
(b) How do oral pills prevent pregnancy ? (CCE 2011)
Answer:
(a)

1. Gonorrhoea caused by bacterium Neisseria gonorrhoeae
2. Syphilis caused by bacterium Treponema pallidum.

(b) Oral pills contain progestin (= progesterone) alone or in combination with estrogen. They prevent pregnancy by inhibition of ovulation, making uterine wall unsuitable for implantation alongwith unsuitable changes in cervical mucus and activity of fallopian tubes.

Question 45.
Explain how ovary functions both as reproductive organ as well as endocrine gland. (CCE 2011)
Answer:
Reproductive Organ. Ovary produces ova, one every lunar month for possible fertilization and formation of foetus.
Endocrine Gland. Maturing ova or follicles present in ovary secrete oestrogen (= estrogen) while empty follicle develops into corpus luteum that secretes progesterone.

Question 46.
What is the information source in the cell nucleus for making proteins. State the basic events in reproduction.
(CCE 2011)
Answer:

1. Information Source. DNA
2. Basic Events in Reproduction. DNA replication, growth of cellular machinery and cell division.

Question 47.
(a) Why are budding, fragmentation and regeneration considered as asexual type of reproduction ?
(b) Which among the following reproduces by spore formation : Bryophyllum, Rhizopus, Hydra ?
(CCE 2011)
Answer:
(a) Asexual Reproduction: Budding, fragmentation and regeneration are all considered to be modes of asexual reproduction as they involve formation of new individuals from single parents without fertilization or fusion of gametes.
(b) Rhizopus.

Question 48.
Draw labelled diagram of
(a) Spore formation in Rhizopus
(b) Regeneration in Planaria. (CCE 2012)
Answer:
(a)

(b)

Question 49.
“Multicellular organisms cannot divide cell by cell”. List two reasons to justify this statement. (CCE 2012)
Answer:

1. In multicellular organisms, cell by cell division is a method of growth and not a method of multiplication as in unicellular organisms.
2. Multicellular organisms have developed complex and specialised reproductive structures which are not possible in single celled organisms.

Question 50.
(a) Name the process by which pollen grains are transferred from anther to stigma. Mention any one external agent which performs this process in some flowers. .
(b) Differentiate between its two types. Give one example of each. (CCE 2012)
Answer:
(a)

1. Pollination
2. Air/Insects.

(b) Two types, self pollination and cross pollination. Self pollination is transfer of pollen grains from the anther to the stigma of the same flower (e.g., Commeliria, Wheat) while cross pollination is transfer of pollen grains from the anther of one flower to the stigma of another flower of the same species (e.g., Salvia).

Question 51.
(a) Name the organ which helps in providing nutrition to embryo. Where is it located ?
(b) What causes the delivery of child from mother’s uterus ? (CCE 2012)
Answer:
(a) Placenta is the organ which provides nourishment to the embryo. It is formed jointly by embryo and uterus. Placenta is located in the uterus of the mother.
(b) Foetal ejection reflex is produced in response to signals from fully formed foetus and its supporting placenta.

Question 52.
List the modes of pollination and define each of them. (CCE 2012)
Answer:
Pollination is of two types, self pollination and cross pollination.
Self Pollination. It is the transfer of pollen grains from the anther to the stigma of the same flower, e.g., Commelina, Wheat.
Cross Pollination. It is the transfer of pollen grains from the anther to the stigma of another flower of the same species, e.g., Salvia.

Question 53.
(a) Differentiate between unisexual and bisexual flowers.
(b) Which of the following plants produce unisexual flowers : Watermelon, Hibiscus, Mustard, Papaya ?
(CCE 2012)
Answer:
(a) Unisexual flowers are those flowers which possess only one type of reproductive organs, either stamens or carpels. Bisexual flowers are those flowers which have both the types of reproductive organs, i.e., stamens and carpels.
(b) Watermelon, Papaya.

Question 54.
(a) List two events during binary fission in Amoeba.
(b) In which two of the following organisms, regeneration takes place : Lion, Planaria, Hydra, Lotus. (CCE 2012)
Answer:
(a)

1. Elongation of nucleus followed by division into two.
2. Cleavage of cytoplasm in between the two daughter nuclei to form two daughter cells.

(b) Regeneration. Planaria, Hydra.

Question 55.
(a) Which organ is responsible for implantation of zygote ?
(b) State the function of fallopian tubes. (CCE 2012)
Answer:
(a) Zygote (in the form of blastocyst) gets implanted in uterus with the help of villi.
(b)

1. Fallopian Tubes,
2. Conduct ovum from ovary to uterus,
3. Fertilization occurs inside fallopian tube.

Question 56.
(a) Name the structure in human male reproductive system that delivers the sperms from the testes to the urethra.
(b) Name the structure in human female reproductive system which delivers the egg from the ovary to the uterus.
Answer:
(a) Vas deferens
(b) Fallopian tube.

Question 57.
(a) Write the advantage of sexual reproduction over asexual reproduction.
(b) Name the male and female parts of a flower. (CCE 2012)
Answer:
(a) Advantage of Sexual Reproduction. Sexual reproduction introduces variations and maintains the vigour and vitality of the individuals.
(b) Male—Stamens.
Female—Carpels.

Question 58.
(a) Differentiate between reproduction and regeneration.
(b) Name any two organisms which grow by regeneration. (CCE 2012)
Answer:
(a) Reproduction is the formation of new individuals by the grown up organisms with the help of propagules or germ cells. Regeneration is growth of injured parts of the individuals for repair and replacement of lost parts.
(b) Planaria and Hydra can grow by regeneration.

Question 59.
What is pollination ? How does it take place ? (CCE 2012)
Answer:
Pollination is the transfer of pollen grains from an anther to a stigma. Pollination between anther to the stigma of the same flower is called self pollination. It occurs through contact between the two.
Pollination between anther of one flower and stigma of another flower is cross pollination. It requires an external agency which may be abiotic (wind, water) or biotic (insects, birds, bats, worms, etc.).

Question 60.
How is the process of binary fission in Amoeba different from that of Leishmania ? (CCE 2012)
Answer:
In Amoeba, binary fission can occur in any plane. In Leishmania the plane of division is vertical.

Question 61.
Which parts/organs of the human reproductive system perform the following functions
(a) Site of fertilisation
(b) Production of ovum. (CCE 2012)
Answer:
(a) Site of Fertilisation. Ampulla-isthmus junction of fallopian tube.
(b) Production of Ovum. Ovary.

Question 62.
Which parts/organs of human reproductive system perform the following functions :
(a) Site of implantation of zygote
(b) Entry of sperms in female reproductive system. (CCE 2012)
Answer:
(a) Implantation. Uterus,
(b) Entry of Sperms. Vagina.

Question 63.
Give any two differences between radicle and plumule. (CCE 2012)
Answer:

1. Radicle is the future root while plumule is the future shoot.
2. Radicle does not bear leaf primordia that are present over the plumule.

Question 64.
List the suitable difference between pollen grain and ovule. (CCE 2012)
Answer:

1. Pollen grain is a spore while ovule is a sporangium.
2. Pollen grain is specialised to produce two male gametes. An ovule has generally a single female gamete.

Question 65.
“The chromosome number of sexually reproducing parents and their offspring is the same”. Justify this statement.
(CCE 2013)
Answer:
Both parents and their offspring have generally diploid chromosomes. Meiosis occurs during gamete formation so that gametes have haploid chromosomes. Fusion of gametes during sexual reproduction produces diploid zygote. The offspring develops from zygote.

Question 66.
(a) Trace the path of sperms from where they are produced in human body to the exterior.
(b) Write the functions of secretions of prostate çland and seminal vesicles in humans. (CCE 2013)
Answer:
(a)

Testis —> Epididymis —> Vas deferens —>Urinogenital duct

(b) Both the glands produce semen plasma, 60—70% by seminal vesicles and 20—30% by prostate gland. It is required for activation and transport of sperms.

Question 67.
List four methods of asexual reproduction other than fission in the living organisms. (CCE 2014)
Answer:
Budding, Fragmentation, Regeneration, Sporulation.

Question 68.
Draw labelled diagrams to illustrate budding in Hydra. (CCE 2014)
Answer:

Question 69.
Students were asked to observe the permanent slides showing different stages of budding in yeast under the high power of microscope.
Answer:
(a) Which adjustment screw (coarse / fine) were you asked to move to focus the slides ?
(b) Draw three diagrams in correct sequence showidg budding in yeast.
Answer:
(a) Fine adjustment
(b)

Question 70.
While observing a slide of budding in yeast, a student performs the following steps :

1. Place the slide on the stage and fix it using the clip,
2. Adjust the mirror and diaphragm.
3. Focus using low power,
4. Adjust to high power. Are the sequence steps correct ? If not correct the sequence of steps. (CCE 2015)

Answer:
Correct.

Question 71.
A student was asked to identify a difference in the nucleus of binary fission of Amoeba and budding in yeast.
What would be the possible correct difference identified by her ? (CCE 2015)
Answer:
In binary fission of Amoeba, the nucleus divides first (before the cleavage of cytoplasm). In budding of yeast, nucleus divides later after the formation of protuberance for bud.

Question 72.
Draw a well labelled diagram of budding in yeast. (CCE 2015)
Answer:

Question 73.
Name the type of asexual reproduction in which two individuals are formed from a single parent and the parental identity is lost. Draw the initial and the final stages of reproduction. State the event with this reproduction starts. (CCE 2015)
Answer:
Binary fission,

Binary fission starts with elongation and cleavage of nucleus.

Question 74.
A student observed the slide of binary fission of Amoeba under a microscope. What should be the observation reproted by him ? (CCE 2015)
Answer:
Study two permanent slides of Amoeba, one showing binary fission and other showing structure of the protozoan.
Nucleus is darkly stained. It appears elongated and constricted in the slide depicting binary fission. The same slide also
shows constriction of the body around the area of constricting nucleus.

Question 75.
What is meant by budding ? Explain with an example. (CCE 2015)
Answer:
Budding in Hydra. Some reserve cells present in the lower half of Hydra begin to divide due to some
internal or external stimulus. They form a cellular mound which grows into a bud. Soon the bud develops a mouth and tentacles. It makes the bud nutritionally independent. The bud constricts from base and separates as a new individual.

Question 76.
What does the diagram given here correctly illustrate ? Give reason in support of your answer.
(CCE 2015)

Answer:
Binary fission in Amoeba.
Reasons :

1. Presence of elongated nucleus undergoing cleavage.
2. Presence of pseudopodia.

Question 77.
Write two differences between binary fission and multiple fission in tabular form.
(CCE 2015)
Answer:

Binary Fission	Multiple Fission
1. Products. It gives rise to two individuals.	It forms several (more than two) individuals.
2. Conditions. Binary fission occurs under favourable conditions.	Multiple fission occurs both under favourable and unfavourable conditions.
3. Nucleus. Nucleus of the parent cell divides only once to form two daughters.	Nucleus of the parent undergoes repeated divisions to form a number of daughter nuclei.
4. Cytoplasm. Cytoplasm undergoes cleavage after each nuclear division.	Cytoplasm does not divide after every nuclear division.
5. Residue. No part of the parent body is left unused.	A part of the body, covering and residual cytoplasm, is left behind.
Examples. Amoeba, Paramecium.	Examples. Plasmodium, Amoeba (encysted).

Question 78.
Draw a labelled diagram to show that particular stage of binary fission in Amoeba in which its nucleus elongates and divides into two and a constriction appears in its cell membrane. (CBSE Delhi 2016)
Answer:

Question 79.
In which asexual reproduction two individuals are formed from a single parent whose identity is lost ? Draw  the initial and final stages of this type of reproduction to justify your answer. Write the event with which this process starts. (CBSE Foreign 2016)
Answer:
Binary fission, e.g., Amoeba. first (initial) and third (final).

Question 80.
A student is observing a permanent slide showing sequentially the different stages of asexual reproduction taking place in yeast. Name this process and draw diagrams of what he observes in a proper sequence.
(CBSE A.I. 2016)
Answer:
Budding.

Short Answer Questions (3 Marks Each)

Question 1.
Define any three of the following terms used in relation to human reproduction,

1. Fertilization (fertilisation)
2. Implantation
3. Placenta
4. Gestation
5. Parturition
6. Ovulation.
   (CBSE Foreign 2005, CCE 2011, 2012)

Answer:

1. Fertilization: The union of male gamete (sperm) with the female gamete (ovum) to form a diploid zygote is called fertilization.
2. Implantation: Fixation of young embryo (blastocyst stage) in the wall of uterus is called implantation.
3. Placenta: It is a spongy vascular structure formed by the joint activity of maternal and foetal tissues in the wall of uterus that is meant for attachment, nourishment and waste disposal for the foetus.
4. Gestation: It is a period between conception and birth of the live young one in mammals that is passed in the body of the mother.
5. Parturition: The act of giving birth to a baby is called parturition.
6. Ovulation: It is liberation of ovum from the ovary which in human beings occurs on 13-14 day of menstrual cycle due to surge of LH secretion.

Question 2.
Explain the terms “fission” and “regeneration” as used in relation to reproduction. (CBSE A. I. 2005)
Answer:
Fission. It is a mode of asexual reproduction in unicellular organisms in which a parent cell divides to form two or more individuals. In binary fission, a parent cell divides into two similar daughters, e.g., Amoeba, Paramecium, Leishmania. In multiple fission the contents of a unicellular individual divide into several daughters, e.g., Plasmodium.
Regeneration. It is the ability of an individual to form lost or broken part, sometimes the entire individual from a piece of the parent body through dedifferentiation of mature cells and activity of reserve cells. The ability to form a new individual from a part of the body is well developed in simple animals like Hydra and Planaria. It is restricted to the formation of only broken parts in complex organisms.

Question 3.
What is pollination. Name its two types. How do they differ from each other ?
(CBSE Delhi 2006, 2016, CCE 2011, CBSE Foreign 2016)
Answer:
Pollination: The transfer of pollens from anther to the stigma of a flower is called pollination.
Types: There are two types of pollination— self pollination and cross pollination.
Differences:

Self Pollination	Cross Pollination
1. Flowers. It is the transfer of pollen grains from anther to stigma of same or genetically similar flower.	It is the transfer of pollen grains from the anther of one ‘ flower to the stigma of another flower.
2. Pollen. Pollen grains are produced in small number.	Pollen grains are produced in large number.
3. Agency. An external agency is not required.	An external agency is required for carrying of pollen grains from one flower to another.
4. Variations. It does not produce variations.	It brings about a lot of variations.
5. Vigour. There is a slow loss of vigour in self pollinated plants.	Vigour of the plants is maintained.
Ex. Commelina, Viola, Wheat.	Ex. Salvia, Bottle Brush, Bombax.

Question 4.
What is vegetative propagation ? When is it used ? Name three methods of vegetative propagation.
(CBSE A.I. 2006 C)
Answer:
Vegetative Propagation: It is the formation of new plants from vegetative parts (e.g., stem, leaf, root, bud) of a parent plant.
When Used: Vegetative propagation is carried out during favourable period for obtaining fast growth of economically and horticulturally important plants. It is the only known method of propagation in seedless species and varieties of plants, e.g., Sugarcane, Banana.
Methods:

1. Cuttings. Generally of stems but can also be of roots and leaves,
2. Layering
3. Grafting.
4. Tissue culture or micropropagation is the latest technique for rapid multiplication of plants.

Question 5.
(a) What is fertilization ? Distinguish between external fertilization and internal fertilization.
(b) What is the site of fertilization in human beings ? (CBSE Delhi 2007)
Answer:
(a) Fertilization: The union of male gamete (sperm) with the female gamete (ovum) to form a diploid zygote is called fertilization.
Differences Between External and Internal Fertilization.

External Fertilization	Internal Fertilization
1. Place. Fertilization occurs outside the body of the female.	Fertilization occurs inside the body of the female.
2. Release of Gametes. Both the sexes discharge their gametes outside their body.	Only the male discharges the gametes and that also in the reproductive tract of the female. The female retains its gametes.
3. Surety. It is not a sure method.	It is a sure method of fertilization.
4. Embryo. Embryo develops unprotected, outside the body of the female.	Embryo is generally well protected but may develop outside or inside the body of the female.
Examples. Fishes, Amphibians.	Examples. Reptiles, Birds, Mammals, Insects, Spiders.

(b) Site of Fertilization. Ampulla part of fallopian tube.

Question 6.
Define the terms unisexual and bisexual giving one example of each. (CBSE Delhi 2007)
Answer:
Unisexual. It is an organism having male and female sex organs on two different types of individuals, e.g., humans, Papaya.
Bisexual. It is an organism having both male and female sex organs present in the same individual, e.g., Rose, Mustard, Earthworm.

Question 7.
Explain double fertilization in plants. (CBSE A.I. 2007)
Answer:
Definition. The phenomenon of two male gametes fusing with different cells in the same embryo sac to produce two different structures is called double fertilization.
One male gamete fuses with oosphere (egg) to form diploid zygote. It is called generative fertilization. Zygote grows to form embryo. The second male gamete fuses with diploid secondary nucleus of central cell. It produces a triploid primary endosperm cell. The fusion is called triple fusion or vegetative fertilization. It produces a nutritive tissue called endosperm.

Question 8.
Illustrate the following with the help of suitable diagrams :
(i) Binary fission in Amoeba
(ii) Leaf of Bryophyllum with Buds. (CBSE A.I. 2008 C)
Answer:
(i) Binary Fission: It means ‘splitting into two’. Binary fission occurs under favourable conditions. When the unicellular individual has become mature, it divides to form two similar individuals. The parent disappears as its body gets distributed into its daughters. For binary fission, the nucleus or nuclear matter elongates and then divides into two. It is followed by cleavage of cytoplasm in between the two daughter nuclei to form two daughter individuals. In Amoeba, binary fission can occur in any plane (Fig. 3.1).

It occurs in a definite plane in unicellular organisms having more oganisation in their bodies. In Paramecium the plane of division is transverse. It is vertical in Euglena and Leishmania (the protozoan that has whip-like flagellum at one end and causes kala azar).
(ii) Leaf of Bryophyllum with Buds.

Buds occur in notches of Bryoplyllum leaf. They do not sprout in the intact leaf. However, when the leaf falls down and comes in contact with the soil, the buds sprout and produce plantlets.

Question 9.
(a) Explain the terms :

1. Implantation
2. Placenta

(b) What is the average duration of human pregnancy ? (CBSE Delhi 2008)
Answer:
(a)

1. Implantation: Fixation of young embryo (blastocyst stage) in the wall of uterus is called implantation.
2. Placenta: It is a spongy vascular structure formed by the joint activity of maternal and foetal tissues in the wall of uterus that is meant for attachment, nourishment and waste disposal for the foetus.

(b) Duration of Human Pregnancy. 270 days, considered 280 days from the time of previous menstruation.

Question 10.
What are sexually transmitted diseases ? Name four such diseases. Which one of them damages the immune system of human body ? (CBSE Delhi 2009)
Answer:
Sexually Transmitted Diseases(STDs). They are diseases which are transmitted through sexual contact with infected persons.
Examples:

1. Gonorrhoea.
2. Syphilis
3. Genital Warts
4. AIDS.

Damage to Immune System: AIDS caused by HIV (human immunodeficiency virus) damages human immune system because the virus multiplies in macrophages and helper T-4 lymphocytes.

Question 11.
List any three differences between pollination and fertilization.
Answer:

Pollination	Fertilization
1.    Definition: It is transfer of pollen grains from anther to the stigma of a flower. 2.    Step: Pollination precedes fertilization. 3.    Purpose: It carries the male gamete producing pollen grains to the female sex organ. 4. Process: Pollination is a physical process. 5. Occurrence: It occurs only in seed plants.	It is the fusion of male and female gametes. Fertilization occurs only after pollination when the pollen grain has germinated and male gametes are carried into ovule. It actually brings about fusion of gametes. Fertilization is a physico-chemical (biological) process. It occurs in both plants and animals of various types.

Question 12.
What is the full form of DNA ? Name the part ‘of the cell where it is located. Explain its role in the process of reproduction of the cell. (CBSE Delhi 2010)
Answer:
DNA: Deoxyribo-nucleic acid.
Location: Mostly in nucleus (small amount also in mitochondria and plastids).
Role in Cell Reproduction: DNA carries hereditary information not only for controlling cellular functions but also all the structural and functional traits of organism. It is because of the latter that single celled zygote is able to form the whole multicellular organism. During reproduction there is formation of new cells which must carry the same amount and type of hereditary information as present in the parent cell. This is accomplished by DNA copying, which occurs prior to each cell division. DNA copying is not error proof. Errors give rise to variations.

Question 13.
Explain vegetative propagation with the help of two examples. List two advantages of vegetative propagation.
(CBSE Delhi 2010)
Answer:
Vegetative propagation is the formation of new plants from vegetative propagules or parts (stem, leaf, root, bud) of a parent plant.

1. Duranta/Bougainvillea. It is multiplied with the help of stem cuttings. 20-30 cm long stem pieces of one year old branches are placed in the moist soil in their natural position during spring or rainy season. The cuttings develop roots and shoots to form new plants.
2. Jasmine/Grape Vine. It is multiplied by layering. One year old basal branch is defoliated in the middle, given a small cut (v-shaped, tongue-like or ring-like), pegged and covered with soil. The branch, now called layer, develops adventitious roots within 1-2 months. It is then separated as new plant.

Advantages:

1. Seedless Plants. Vegetative propagation is the only known method of multiplication of seedless plants, g., Banana, Sugarcane, Pineapple, Jasmine, some varieties of Orange, Rose.
2. Uniform Yield. Seeds and fruits are of uniform quality, size, taste and aroma.
3. Genetic Uniformity. Vegetative propagation gives a genetically uniform population.
4. Good Qualities. Good qualities of a variety can be maintained indefinitely.
5. Survival Rate. Survival rate of the daughters is nearly 100% while in case of seed grown plants, it is 10%.
6. Quicker Method. Vegetatively reproduced plants bear flowers and fruits earlier than the plants raised through seeds. Potato requires only three months for forming a new crop if raised from tubers. It takes 15 months if raised from seeds.                                                            ‘
7. Introduction in New Areas. In areas where seed germination fails to form mature plants, vegetative reproduction can help in establishing the plants.

Question 14.
(a) Identify the asexual method of reproduction in each of the following organisms :

1. Rose
2. Yeast
3. Planaria.

(b) What is fragmentation ? Name a multicellular organism which reproduces by this method. (CCE 2011)
Answer:
(a)

1. Rose —stem cutting
2. Yeast—Budding
3. Planaria —regeneration.

(b) Fragmentation. It is the process of breaking up the body of an organism into two or more parts (called fragments), each of which grows into a new individual. Example. Spirogyra.

Question 15.
(a) How many eggs are produced every month by either of the ovaries in a human female ? Where does fertilization take place in the female reproductive system ?
(b) What happens in case of egg released by the ovary is not fertilized ? (CCE 2011)
Answer:
(a) One egg is produced every month by one of the two ovaries in a human female. Fertilization occurs inside the fallopian tube (ampulla isthmus junction).
(b) If the egg is not fertilized, it lives for one day and is then expelled. This also sets in motion the menstrual cycle. After about 12 days the corpus luteum (empty Graafian follicle) degenerates. In the absence of hormones progesterone and estrogen, the glandular part of endometrial lining is peeled off alongwith discharge of blood and mucus. The process is called menstruation. It lasts for 3-5 days.

Question 16.
In the diagram of the human male reproductive system

(a) Label A and B
(b) Name the hormone produced by X. What is the role of this hormone in human male ?
(c) Mention the name of substances that are transported by tubes C and D.
(CCE 2011)
Answer:
(a) A —seminal vesicle
B — prostate gland.
(b) X— testosterone. Testosterone controls sperm formation, expression of secondary characters and functioning of accessory glands.
(c) C— sperms.
D — semen (including sperms) and urine.

Question 17.
Differentiate between
(a) Asexual and sexual reproduction
(b) Plumule and radicle
(c) Pollination and fertilization. (CCE 2011)
Answer:
(a) Asexual reproduction is monoparental, with no gametes, no meiosis and very little variations. Sexual reproduction is generally biparental involving fusion of gametes, meiosis and lot of variations.
(b) Plumule is the future shoot while radicle is the future root.
(c) Pollination is the transfer of pollen grains from anther to stigma while fertilization is the fusion of male and female gametes.

Question 18.
(a) Why is vegetative propagation practised for growing some types of plants ?
(b) Name the different parts of a flower that has germ cells.
(c) List any two agents of pollination. (CCE 2011)
Answer:
(a)

1. Seedless plants can be propagated only vegetatively, e.g, Banana, Sugarcane,
2. Others are propagated vegetatively to obtain flowers and fruits early.

(b) Stamen —Pollen —Male Germ Cells.
Carpel—Ovary — Ovule — Embryo sac — Female Germ Cell.
(c) Wind (anemophily), insects (entomophily).

Question 19.
(a) What is the difference between self and cross pollination ?
(b) What happens to the pollen which falls on a suitable stigma ? Explain. (CCE 2011)
Answer:
(a) Self pollination is transfer of pollen grains from the anther to the stigma of the same flower (e.g., Commeliria, Wheat) while cross pollination is transfer of pollen grains from the anther of one flower to the stigma of another flower of the same species (e.g., Salvia).
(b) After falling on a suitable stigma the pollen absorbs water and nutrients. It produces a pollen tube that grows through the style and reaches the ovary. Its tip contains a tube nucleus and two male gametes. The pollen tube enters an ovule, strikes against one synergid of the embryo sac and bursts open to release its contents. One male gamete fuses with the egg to form zygote while the other fuses with secondary nucleus to produce primary endosperm nucleus.

Question 20.
Name the parts A, B and C and state one function of each part. (CCE 2011, CBSE Delhi 2016)

Answer:
A —anther — formation of pollen.
B—style—lifting stigma to receive pollen.
C—ovary—contains ovules which later develop into seeds while ovary forms the fruit.

Question 21.
State one function each of the following parts of human male reproductive system :

1. Vas deferens
2. Testis
3. Prostate Gland. (CCE 2011)

Answer:

1. Vas Deferens: Passage of sperms (hence sperm duct).
2. Testis: Produces sperms and male sex hormone called testosterone.
3. Prostate Gland: Forms 20-30% of semen, essential for sperm motility.

Question 22.
(a) Name an organism in which binary fission occurs in a definite orientation.
(b) Draw a neat diagram of germinating seed and label on it the following : Cotyledon, Plumule, Radicle. (CCE 2011)
Answer:
(a) LeishmanialEuglena
(b)

Question 23.
(a) Name the parts 1 to 5 of human female reproductive system

(b) Name the part in which fertilization takes place in the system.
(CCE 2011)
Answer:
(a) 1 — fallopian tube,
2 — ovary,
3 — Uterus,
4 — cervix,
5 — vagina.
(b) Fallopian tube.

Question 24.
(a) How do oral pills function as contraceptives ?
(b) The use of these pills may be harmful. Why ? (CCE 2011)
Answer:
(a) Oral pills prevent ovulation as they contain progesterone with or without estrogen.
(b) Use of oral pills may cause some side effects because they do change the hormonal balance of the body.

Question 25.
(a) Draw a neat diagram of female reproductive system in human beings and label on it :

1. The part which secretes ova
2. The part where implantation takes place.

(b) What happens if fallopian tube is blocked ? (CCE 2011)
Answer:
(a)

Label

1. Ovary (Produces ova)
2. Uterus (implantation).

(b) Blockage of fallopian tube will prevent fertilization.

Question 26.
State in brief the function of the following organs in the human female reproductive system,
(a) Ovary
(b) Fallopian tube
(c) Uterus. (CCE 2011)
Answer:
(a) Ovary: Formation of ova and secretion of hormones, estrogen and progesterone.
(b) Fallopian Tube: Passage of ovum, site for fertilization.
(c) Uterus: Implantation and nourishment of embryo.

Question 27.
(a) Name a unisexual flower,
(b) Name the organ known as “birth canal” in female reproductive system.
(c) Mention two factors that determine the size of population. (CCE 2011)
Answer:
(a) Papaya, Watermelon,
(b) Vagina
(c) Birth rate or natality and death rate or mortality.

Question 28.
Draw a neat diagram of germination of pollen on stigma. Also label on it the following parts :

1. Female germ cell
2. Pollen tube
3. Pollen grain
4. Male germ cell. (CCE 2011, 2012)

Answer:

Question 29.
Explain the following methods of contraception giving one example of each

1. Barrier method
2. Hormonal imbalance method
3. Surgical method.  (CCE 2011)

Answer:

1. Barrier Method. Mechanical Barrier Methods. They prevent passage of sperms into genital tract of the female.
   1. It is tubular latex sheath to be worp over male copulatory organ during sex.
   2. Cervical Cap. It is a rubber nipple to be fitted over cervix,
   3. Contraceptive Diaphragm. It is tubular sheath that is fitted in vagina during sex.
2. Hormonal Imbalance Method. It is commonly carried out by the ladies through regular use of oral pills. They inhibit ovulation through suppression of FSH.
3. Surgical Method. It is of two types :
   1. Vasectomy. The two vasa deferentia of the male are blocked by cutting and tying.
   2. Tubectomy. The two fallopian tubes of the female are blocked by cutting and tying or ligating.

Question 30.
Expand AIDS. List any four methods of prevention (control) of AIDS. (CCE 2011)
Answer:
AIDS—Acquired Immune Deficiency Syndrome.
Methods of Prevention

1. Avoiding unprotected sex.
2. Use of disposable syringes and needles
3. Use of disposable blades and razors,
4. Compulsorily complete sterilization of all equipment used in dental treatment and surgery.
5. Proper screening of blood before transfusion.

Question 31.
(a) Name any sexually transmitted disease which is

1. caused by virus
2. caused by bacteria.

(b) What may be the possible reasons for adopting contraceptives for sex ? Mention any two. (CCE 2012)
Answer:
(a)

1. Bacterial STD: Gonorrhoea by Neisseria gonorrhoeae
2. Viral STD: Genital warts by Human Papilbma Virus,

(b) Reason: Preventing pregnancy for

1. Limiting size of family,
2. Spacing birth of children so as to provide proper care to each child. .

Methods:

1. Barrier method like condom and diaphragm
2. Intrauterine device like copper-T
3. Oral pills.

Question 32.
State in brief the role of human male reproductive system. Why is it called the urinogenital system ?
(CCE 2012)
Answer:
Role:

1. Human male reproductive system synthesises sperms in seminiferous tubules of testes. The testes lie in a pouch of skin or scrotum outside the abdomen to provide 1°-3°C temperature lower than that of body.
2. Leydig cells present in the connective tissue of testes secrete male sex hormone or testosterone for maintaining the secondary male sex traits,
3. The sperms are stored in epididymes and passed out at the time of ejaculation when secretions from seminal vesicles, prostate gland and Cowper’s glands mix with them to form semen. Urinogenital System. The passage way of male reproductive system is common with the passage of urine from the body. Therefore, male reproductive system is also called urinogenital system.

Question 33.
(a) Explain the process of budding,
(b) Show in sequence the process of budding in Hydra with the help of diagram. (CCE 2012, 2013)
Answer:
(a) Budding is the formation of an outgrowth from an organism which grows and separates to form a new individual. It is a mode of asexual reproduction in both unicellular (e.g., Yeast) and multicellular (e.g., Hydra) organisms.
(b) Budding in Hydra. Some reserve cells present in the lower half of Hydra begin to divide due to some
internal or external stimulus. They form a cellular mound which grows into a bud. Soon the bud develops a mouth and tentacles. It makes the bud nutritionally independent. The bud constricts from base and separates as a new individual.

Question 34.
Give a reason for each of the following :
(a) Regeneration is not considered a method of reproduction.
(b) Blocking of the fallopian tube causes birth control,
(c) Spores generally have a thick wall. (CCE 2012)
Answer:
(a) Regeneration is not the same as reproduction as no propagule is formed and no organism will depend on being cut to be able to reproduce.
(b) Blocking of fallopian tubes will not allow the sperms to reach the ovum.
(c) Spores are a means of dispersal as well as perennation. They have to be thick-walled to tolerate adverse environmental conditions.

Question 35.
(a) Draw a neat labelled diagram of a germinated seed and label radicle, plumule and cotyledon.
(b) Mention function of each of these parts. (CCE 2012)
Answer:
(a)

(b)

1. Radicle: It forms the first root of the seedling,
2. Plumule: It grows to form the shoot of the seedling,
3. Cotyledon: It stores food and supplies the same to embryo axis for its growth.

Question 36.
(a) Differentiate between binary and multiple fission. Name an organism that reproduces by multiple fission.
(b) Vegetative reproduction is beneficial to plants that are propagated asexually. Give two advantages.
(CCE 2012)
Answer:
(a) In binary fission a unicellular organism divides into two equal daughters. In multiple fission it gives rise to several (more than 2) individuals. Some residue may be left in multiple fission while no such wastage occurs in binary fission.
Multiple fission occurs in Plasmodium (Malaria Parasite).
(b) Vegetative Reproduction,

1. It is the only known method of multiplication in seedless plants like Banana and Sugarcane,
2. It is quicker method of multiplication with a crop of uniform yield.

Question 37.
(a) Name any two plants that reproduce through grafting.
(b) List any two benefits to an organism that reproduces through spores. (CCE 2012)
Answer:
(a) Grafting. It is performed in case of high quality Apple, Mango, Pear and some other plants.
(b) Benefits of Spore Formation,

1. Spores are a means of dispersal.
2. They are often thick-walled and take part in perennation.
3. A large number of spores are often formed at one time so that rapid multiplication can occur.

Question 38.
List any four methods of contraception used by humans. How does their use have a direct effect on health and prosperity of the family ? (CCE 2013, 2014)
Answer:
Methods of Contraception:

1. Mechanical Barriers like condoms, cervical cap, diaphragm.
2. Oral Contraceptives or oral pills like Mala D, Saheli
3. Intrauterine Contraceptive Devices (IUCD) like loop, bow, Cu-T.
4. Surgical Methods like vasectomy in males and tubectomy in females.

Effects:

1. Enjoying a good reproductive health.
2. Protecting from sexually transmitted diseases.
3. Restricting the number of children.
4. Spacing the birth of children so as to properly look after them, provide them proper education without depleting the resources of the family.
5. Controlling population.

Question 39.
(a) Explain the process of regeneration in Planaria. (CCE 2014)
(b) How is regeneration different from reproduction ? (CCE 2013, 2014)
Answer:
(a) Regeneration in Planaria. In Planaria, a broken piece of the body grows the missing parts and forms the complete animal. This occurs with the help of reserve or stem cells and dedifferentiation of differentiated cells. They proliferate to form mass of cells which differentiate into various types of cells and tissues just like development in the young animal.

(b) Reproduction is the formation of new individuals by the grown up organisms with the help of propagules or germ cells. Regeneration is growth of injured parts of the individuals for repair and replacement of lost parts.

Question 40.
Write two examples each of sexually transmitted diseases caused by

1. virus
2. bacteria.

Explain how the transmission of such diseases be prevented ? (CCE 2013)
Answer:

1. Viral STDs. Genital warts by human papilloma virus (HPV), AIDS by human immunodeficiency virus (HIV).
2. Bacterial STDs. Gonorrhoea by Neisseria gonorrhoeae, Syphilis by Treponema pallidum.

Question 41.
Prevention. Sexually transmitted diseases can be prevented by use of mechanical barriers, especially condoms.
(a) Name the following :

1. Thread like non-reproductive structures present in Rhizopus.
2. Blobs, that develop at the tip of the non-reproductive threads in Rhizopus.

(b) Explain the structure and function of structures released from the blobs in Rhizopus. (CCE 2013)
Answer:
(a)

1. Hyphae (singular hypha).
2. Sporangia (singular sporangium).

(b) The structures released by blobs or sporangia are spores. Spores of Rhizopus are thick walled dark coloured and multinucleate. They are dispersed by air. After falling on a suitable substratum, each spore gives rise to a new mycelium.

Question 42.
(a) Define pollination. Why is it necessary for reproduction in flower bearing plants ?
(b) Write one reason to explain why cross pollination is preferred over self pollination ? (CCE 2013)
Answer:
(a) Pollination is the transfer of pollen grains from anther to the stigma. It is essential because the male gametes of flower bearing plants are nonmotile. On stigma a pollen grain germinates and sends male gametes to embryo sac by means of a pollen tube.
(b) Cross pollination produces variations and maintains vigour of the plants.

Question 43.
What are the advantages of sexual reproduction over asexual reproduction ? (CCE 2013)
Answer:
“significance of Sexual Reproduction”

1. Due to reshuffling of chromosomes and crossing over, sexual reproduction brings about variations in almost all characters so that no two individuals are similar. Variations are essential for recognition, individuality and competitiveness. They may not protect individuals under adverse conditions but survival of species depends upon pre-adaptive variations.
2. Better Adaptability. Increased variability due to sexual reproduction is helpful to organisms in better adaptability to changes in environment.
3. Vigour and Vitality. It maintains the vigour and vitality of the individuals.
4. Harmful Traits. Harmful traits are often kept suppressed because of reshuffling of gene pairs that occurs during gamete formation and fusion.
5. Near Uniformity of Population. Due to the flow of genes amongst individuals during sexual reproduction, the uniformity of population is maintained where there is a broad resemblance of all the individuals with one another.
6. Genetic changes brought about by sexual reproduction play an important part in evolution of new forms.

Question 44.
Draw diagrams to explain the regeneration that takes place in each of the body parts of Planaria when its body is cut into three pieces. Name any other organism in which a similar process can be observed.
(CCE 2014)
Answer:
(a)

(b) Hydra.

Question 45.
On cutting the body of an organism into many pieces, it was observed that many of these pieces developed as new individuals. Name the process and list two organisms in which this process may be observed. Draw a schematic diagram to illustrate the changes that are likely to be observed during the development of new individuals in any one of the organisms named. , (CCE 2014)
Answer:
(i) Regeneration,
(ii) Planaria, Hydra.

Question 46.
Write one difference between asexual and sexual modes of reproduction. Which species is likely to have better chances of survival, the one reproducing asexually or the one reproducing sexually ? Justify your answer.
(CCE 2014)
Answer:
(a) Difference: Asexual reproduction is monoparental, with no gametes, no meiosis and very little variations. Sexual reproduction is generally biparental involving fusion of gametes, meiosis and lot of variations.
(b) Better Chances of Survival. Sexually reproducing.
Reason: 

1. Due to reshuffling of chromosomes and crossing over, sexual reproduction produces variations in alomost all characters,
2. Sexual reproduction maintains as well as improves vigour and vitality of the individuals,
3. Variability and vitality are helpful to organisms in better adaptability to environment.

Question 47.
What is the effect of DNA copying which is not perfectly accurate on the reproductive process ? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals? (CCE 2014)
Answer:
(a) Inaccuracy in DNA Copying . Even small errors of DNA copying produce variations or mutations. Some of these mutations may be drastic as to kill the cells and stop the reproductive process. Others are minor and form the basis of varied traits.
(b) DNA Amount: The parents are diploid (2n) as each of them has two sets of chromosomes (DNAs). They form haploid (In) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes (DNAs). During fertilization, one male gamete fuses with one female gamete. It restores the diploid (2n) chromosome/DNA number in the offspring that is formed from fusion product or zygote (2n).

Question 48.
(a) How would you relate the following methods to asexual reproduction :

1. Binary fission
2. Spore formation ?

(b) State any advantage of using sexual reproduction over asexual reproduction. (CCE 2014)
Answer:
(a) Asexual reproduction is the formation of new individuals from a part of a single parent without formation and fusion of gametes.

1. In binary fission a fully grown unicellular individual divides into two similar individuals or daughters directly.
2. In spore formation a single cell or sac of the parent produces a number of reproductive bodies which get dispersed and form new individuals on germination. There is no meiosis or gamete formation in both the cases.

(b) Advantage of Sexual Reproduction. Sexual reproduction introduces variations and maintains the vigour and vitality of the individuals.

Question 49.
Name the type of asexual reproduction demonstrated by the following organisms :
(a) Amoeba
(b) Rhizopus
(c) Planaria
(d) Plasmodium
(e) Spirogyra
(f) Bryophyllum. (CCE 2014)
Answer:
(a) Amoeba. Binary fission.
(b) Rhizopus. Spore formation or sporulation
(c) Planaria. Regeneration
(d) Plasmodium. Multiple fission,
(e) Spirogyra. Fragmentation
(f) Bryophyllum. Vegetative reproduction by foliar buds.

Question 50.
List six specific characteristics of sexual reproduction. (CCE 2015)
Answer:

1. Biparental
2. Meiosis
3. Haploid gametes
4. Fertilization
5. Diploid zygote
6. Variations.

Question 51.
What are chromosomes ? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained. (CCE 2015)
Chromosomes are linear strands of DNA and associated proteins that occur in nucleus of eukaryotic cells, carry genes and function in transmission of hereditary information. (CCE 2015)
Answer:
The parents are diploid (2n) as each of them has two sets of chromosomes (DNAs). They form haploid (In) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes (DNAs). During fertilization, one male gamete fuses with one female gamete. It restores the diploid (2n) chromosome/DNA number in the offspring that is formed from fusion product or zygote (2n).

Question 52.
List four points of significance of reproductive health in a society. Name any two areas related to reproductive health which have improved over past 50 years in our country.
Answer:

1. People can lead a safe, responsible and satisfying reproductive life.
2. Provides protection from catching STDs.
3. Advantage of small family, care of the children as well as their proper upbringing
4. Less mortality among the new borns.
5. Maintenance of proper health of the mother and lesser chances of maternal mortality.

Improvement :

1. Reduction in the rate of population growth.
2. Decrease in the spread of STDs.
3. Adoption of small family norm.

Question 53.
Explain how surgical methods used for men and women respectively help in contraception.
Answer:
Reversible Sterilisation: It is surgical technique that prevents passage of sperms in males and ova in females. The technique is called reversible because by another surgical procedure the passage-way can be restored. Reversible sterilisation is otherwise permanent method of contraception. It is of two types, vasectomy in males and tubectomy in females.

1. Vasectomy: The two vasa deferentia of the male are blocked by cutting a small piece and tying the rest. This prevents passage of sperms from testes into semen.
2. Tubectomy: A portion of both the fallopian tubes is excised or ligated to block the passage of ovum.

Question 54.
(a) Define germination.

(b) From the given diagram identify the incorrectly labelled parts.
(CCE 2015)
Answer:
(a) Germination. Beginning of growth or sprouting of a propagule like spore, seed or bud is called germination. It requires a particular set of external and internal conditions.
(b) Incorrectly Labelled Parts :

1. Male germ cell
2. Pollen grain
3. Pollen tube
4. Ovule.

Question 55.
Give reason as to why the following processes are different from each other,
(a) Fission in Amoeba and Plasmodium.
(b) Regeneration and fragmentation.
(c) Binary fission and fragmentation. (CCE 2015)
Answer:
(a) Under favourable conditions Amoeba multiplies by binary fission while Plasmodium multiplies by multiple fission.
(b)

Regeneration	Fragmentation
1.   Process. It is the ability to repair injured parts and grow lost parts. 2.   Cells. Ability of regeneration depends upon the occurrence of stem cells and dedifferentiated cells. 3.   Occurrence. It occurs in more advanced organisms.	It is breaking up the body of an organism into two or more functional parts. The cells of the fragments possess the ability to divide and bring about growth of the fragments. It occurs in organisms having simple structure.

(c)

Fission	Fragmentation
1.  Organisms. It occurs in unicellular organisms. 2.  Nucleocytoplasmic Division. It occurs prior to fission. 3.  Multiplication. It gives rise to new individuals. 4.  Products. The daughters formed after fission are equal. Ex. Amoeba	Fragmentation is found in multicellular organisms. Cells grow and divide after fragmentation. Pieces of the parent individual grow to form daughter individuals. The products of fragmentation are generally unequal anc dissimilar. Ex. Spirogyra.

Question 56.
Budding is type of asexual reproduction used by Hydra.
(a) What is meant by asexual reproduction ? How is it different from sexual reproduction ?
(b) Name any other type of asexual reproduction used by Hydra. Define it.
Answer:
Budding is a mode of asexual reproduction in Hydra as the propagules is a bud or outgrowth of somatic body of the animal.
(a) Asexual reproduction is the formation of new individuals from specialized or unspecialized somatic parts of a single parent.
Difference: Asexual reproduction is monoparental, with no gametes, no meiosis and very little variations. Sexual reproduction is generally biparental involving fusion of gametes, meiosis and lot of variations.
(b) Regeneration: It is the ability of an individual to form lost or broken part, sometimes the entire individual from a piece of the parent body through dedifferentiation of mature cells and activity of reserve cells. The ability to form a new individual from a part of the body is well developed in simple animals like Hydra and Planaria. It is restricted to the formation of only broken parts in complex organisms.

Question 57.
What is the importance of DNA copying during reproduction ? Why are offspring formed by asexual reproduction genetically similar to their parents ? (CCE 2015)
Answer:
Importance of DNA Copying : DNA carries hereditary information not only for controlling cellular functions but also all the structural and functional traits of organism. It is because of the latter that single celled zygote is able to form the whole multicellular organism. During reproduction there is formation of new cells which must carry the same amount and type of hereditary information as present in the parent cell. This is accomplished by DNA copying, which occurs prior to each cell division. DNA copying is not error proof. Errors give rise to variations.
Offspring formed by Asexual Reproduction. Asexual reproduction is uniparental. The genetic material present in the offspring is unaltered copy of DNA present in the parent. Therefore, they are genetically similar to the parents.

Question 58.
(a) A women had undergone surgical method for preventing unwanted pregnancies. Does this protect her from getting sexually transmitted diseases ?
(b) How can AIDS be prevented ? (CCE 2015)
Answer:
(a) No, it does not prevent the coming together of body fluids during sex.
(b) Prevention of AIDS,

1. Use of barrier method of contraception like condom,
2. Protection from getting infected, by blood contact like infected needles, syringes or transfusion,
3. Proper sterilisation of dental equipment,
4. Prevention of sexual contact with AIDS positive persons,
5. Prevention of pregnancy by AIDS positive patients.

Question 59.
Rhizopus is an organism which reproduces by spore formation.
(a) What is meant by spore formation ?
(b) What does the reproductive part or blob of Rhizopus contain ?
(c) Why are these structures protected by thick walls ? (CCE 2015, CBSEA.I. 2017)
Answer:
(a) Spore Formation. It is the formation of minute unicellular asexual reproductive dissemules which on germination give rise to new individuals.
(b) Blob or reproductive part of Rhizopus is sporangium. It contains spores.
(c) Thick Walls of Spores. Spores are dispersed by air currents. They have to face dry, hot, cold and other hostile conditions. Thick wall protects the spores from unfavourable environment.

Question 60.
How does the uterus prepare itself and nurture the growing embryo ? What happens when the egg is not fertilized ? (CCE 2015)
Answer:
Preparation: Under the influence of hormones from pituitary and growing Graafian follicle, the endometrium of uterus thickens, develops blood vessels and glands for nourishing the future embryo.
Nutrition for Growing Embryo. The contact region between embryo and endometrium grows into placenta. Placenta helps the embryo in obtaining nourishment (and oxygen) from blood sinuses of the uterus.
When Egg is not Fertilized: Glands present in the mucosa of uterine endometrium begin to degenerate. This sloughs off the endometrial lining, releasing a lot of mucus and blood. It is called menstruation. Menstruation lasts for 3-5 days.

Question 61.
What do the labelled parts in the diagram work for ? (CCE 2015)

Answer:
Plumule: Formation of shoot.
Cotyledon: Storage of food.
Radicle: Formation of root.

Question 62.

Identify from the diagram the type of reproduction used and the organism showing it. (CCE 2015)
Answer:
A — Hydra, budding (asexual reproduction)
B —Amoeba, binary fission (asexual reproduction)
C — Planaria, regeneration (asexual reproduction).

Question 63.
How do organisms whether reproduced asexually or sexually maintain a constant chromosome number through several generations. Explain with the help of suitable example. (CBSE Delhi 2016)
Answer:
Maintenance of Chromosome Number Over Generations.
In asexual reproduction, new individuals or daughters are formed through mitotic divisions, e.g., Amoeba. There is replication of DNA/chromosomes followed by equal distribution of chromosomes among the daughter cells.
In sexual reproduction chromosome number is ^maintained through two processes, gametogenesis and fertilization. Meiosis occurs during gametogenesis. Here, the chromosome number is halved. For example, human beings with 46 chromosomes produce ova with 23 chromosomes and sperms with 23 chomosomes. Fertilization involving fusion of an ovum (23 chromosomes) with a sperm (23 chromosomes) produces a zygote with 46 chromosomes. The young one develops through mitotic divisions of the zygote so that cells of the grown up individual come to have 46 chromosomes.

Question 64.
What are the functions of testis in the human male reproductive system ? Why are these located outside the abdominal cavity ? Which is responsible for bringing about changes in appearance seen in boys at the time of puberty ? (CBSE Delhi 2016)
Answer:
Functions of Testis. Produces sperms and male sex hormone called testosterone.
Location of Testis. Testes are located outside the abdominal cavity (in testicle behind penis) as maturation of sperms requires a temperature lower by 2°C than that of the body.
Puberty Changes in Boys. They are caused by hormone testosterone.

Question 65.
What is multiple fission ? How does it occur in an organism ? Explain, briefly. Name one organism which exhibits this type of reproduction. (CBSE Delhi 2016)
Answer:
Definition: Multiple fission is a mode of asexual reproduction in a unisexual organism where a single parent produces a number of daughter individuals.
Mechanism: The nucleus of the parent cell divides repeatedly to form a number of daughter nuclei. Cytoplasm gathers around each nucleus followed by development of cell membranes to form daughter cells. The parent cell bursts open to release the daughter individuals.
Example Plasmodium (Malarial Parasite).

Question 66.
What happens when
(a) Planaria gets cut into two pieces
(b) A mature Spirogyra filament attains considerable length
(c) On maturation sporangia burst. (CBSE Foreign 2016)
Answer:
(a) Regeneration in Planaria: In Planaria, a broken piece of the body grows the missing parts and forms the complete animal. This occurs with the help of reserve or stem cells and dedifferentiation of differentiated cells. They proliferate to form mass of cells which differentiate into various types of cells and tissues just like development in the young animal.

(b) Spirogyra: Multiple fission is better as

1. it often occurs inside perennating cysts
2. it produces many daughters.

(c) Sporangium: The mature sporangium bursts to expose spores that are picked up by air and dispersed. On settling at suitable medium each spore germinates and forms a new individual.

Question 67.
What is sexual reproduction ? List its four advantages. (CBSE Foreign 2016)
Answer:
Definition: It is a mode of reproduction in which offspring are formed by the process of formation and fusion of gametes.
Advantages:

1. It brings traits of the two parents in the offspring.
2. It brings about variations due to reshuffling of chromosomes and crossing over.
3. It maintains and improves vigour and vitality of the individuals.
4. It promotes diversity, adaptations and formation of new species.

Question 68.
Name the reproductive parts of an angiosperm. Where are these parts located ? Explain in brief the structure of its female reproductive part. (CBSE Foreign 2016)
Answer:

1. Stamen—male. Carpel-female. They are located in flower.
2. The female part or carpel (=pistil) consists of a terminal receptive stigma, a stalk like style and a basal swollen ovary containing ovules. The ovary later matures into fruit while the ovules form seeds.

Question 69.
(a) Mention the role of the following organs of human male reproductive system :

1. Testis
2. Serotum
3. Vas deferens
4. Prostate gland.

(b) What are the two roles of testosterone. (CBSE Foreign 2016)
Answer:
(a)

1. Testis: Produces sperms and hormone testosterone.
2. Scrotum: Holding the two testes outside the abdominal cavity for providing optimum temperature (2°C less than body temperature) for sperm maturation.
3. Vas Deferens: Passage of sperms from epididyrryis to ejaculatory duct.
4. Prostate Gland: Secretes nutritive fluid for activation of sperms and clotting enzyme for extruded semen.

(b) Testosterone Regulates sperm formation, puberty changes in boys and maintenance of male secondary organs and traits.

Question 70.
Define reproduction. How does it help in providing stability to the population of species ?
(CBSEA.I. 2016)
Answer:
Reproduction is the process of producing new young individuals of similar type by the mature individuals.
Stability: Reproduction maintains the size and composition of population of a species by regularly adding new individuals for replacing the ones getting killed due to ageing, disease or predation. It also adds variations that allow the individuals to adapt to changing environment.

Question 71.
Explain the term “regeneration” as used in relation to reproduction of organisms. Describe briefly how regeneration is carried out in multicellular organisms like Hydra. (CBSE A.I. 2016)
Answer:
Regeneration. It is the ability of an organism to form a complete individual from a piece of the parent body (Regeneration also involves the formation of lost parts by an individual).
Lowly organised multicellular organisms like Hydra have the ability to reproduce through regeneration. For regeneration, the contained stem cells become active. Many differentiated cells undergo dedifferentiation. Both the types of cells proliferate forming a large number of cells. The mass of proliferated cells show differentiation into tissues and organs forming the new individual.

Question 72.
(a) List two reasons for the appearance of variations among the progeny formed by sexual reproduction.

(b)

1. Name the part marked ‘A’ in the diagram,
2. How does ‘A’ reach part ‘B’ ?
3. State the importance of part ‘C’.
4. What happens to the part marked ‘D’ after fertilization is over ? (CBSE A.I. 2016)

Answer:
(a)

1. Coming together of the chromosomes/traits of the two parents,
2. Reshuffling of chromosomes and crossing over.

(b)

1. Pollen grain,
2. Pollen grains are carried to stigma by the agency of wind, water or insects in the process of pollination,
3. It is pollen tube formed on germination of pollen grain. The same carries male gametes to the female gamete,
4. In fertilization the egg is converted into zygote which gives rise to embryo.

Question 73.
In context of reproduction of species, state the main difference between fission and fragmentation. Also give one example of each.
Answer:

Fission	Fragmentation
1.  Organisms. It occurs in unicellular organisms. 2.  Nucleocytoplasmic Division. It occurs prior to fission. 3.  Multiplication. It gives rise to new individuals. 4.  Products. The daughters formed after fission are equal. Ex. Amoeba	Fragmentation is found in multicellular organisms. Cells grow and divide after fragmentation. Pieces of the parent individual grow to form daughter individuals. The products of fragmentation are generally unequal anc dissimilar. Ex. Spirogyra.

Question 74.
What happens when
(a) Accidentally, Planaria gets cut into many pieces ?
(b) Bryophyllum leaf falls on the wet soil
(c) On maturation, sporangia of Rhizopus burst.
(CBSE Delhi 2017)
Answer:
(a) Regeneration in Planaria. In Planaria, a broken piece of the body grows the missing parts and forms the complete animal. This occurs with the help of reserve or stem cells and dedifferentiation of differentiated cells. They proliferate to form mass of cells which differentiate into various types of cells and tissues just like development in the young animal.
(b) Leaves of Bryophyllum bear adventitious buds in the marginal notches.
(c) As the leaves fall down on the ground and come in contact with soil, the buds sprout and form new plants.

Question 75.
(a) State the basic requirement for sexual reproduction ?
(b) Write the importance of such reproduction in nature. (CBSE Dlehi 2017)
Answer:
(a) Basic Requirement :

1. Meiosis and formation of male and female gametes,
2. Fusion of the two types of gametes and formation of diploid zygote.

(b) Importance: It introduces variations or new characters that provide adaptability and increased fitness due to

1. Chance separation of chromosomes during meiosis required for gamete formation,
2. Crossing over during meiosis.
3. Chance coming together of chromosomes during fertilization,
4. Mutations or mistakes during DNA replication.

Question 76.
State the changes that take place in the uterus when
(a) Implantation of embryo has occurred
(b) Female gamete/egg is not fertilised. (CBSE Delhi 2017)
Answer:
(a) Implantation of Embryo has Occurred: Endometrium thickens, becomes glandular and highly vascular. The contact region between embryo and uterine wall grows into placenta. Placenta helps the embryo in obtaining nourishment and oxygen from blood sinuses of the uterus. It also helps in transfer of wastes from embryo to the blood of the mother.
(b) Female Gamete is not fertilized: Glands present in the mucosa of uterine endometrium begin to degenerate. This sloughs off the endometrial lining, releasing a lot of mucus and blood. It is called menstruation. Menstruation lasts for 3-5 days.

Question 77.
Mention the total number of chromosomes alongwith the sex chromosomes that are present in a human female and a human male. Expain how in sexually reproducing organisms the number of chromosomes in the progeny remains the same as that of the parents. (CBSE Delhi 2017)
Answer:
(a) Chromosome Number. Human Female— 44 autosomes + XX sex chromosomes or allosomes.
Human Male. 44 autosomes + XY allosomes.
(b) Same Chromosome Number: The parents are diploid (2n) as each of them has two sets of chromosomes (DNAs). They form haploid (In) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes (DNAs). During fertilization, one male gamete fuses with one female gamete. It restores the diploid (2n) chromosome/DNA number in the offspring that is formed from fusion product or zygote (2n).

Question 78.
List any four steps involved in sexual reproduction and write its two advantages. (CBSE Delhi 2017)
Answer:
Steps:

1. Formation of male and female gametes through meiosis
2. Transfer of male gamete to the area of female gamete.
3. Fusion of the two types of gametes resulting in the formation of diploid zygote.
4. Development of zygote into embryo that grows into a new individual.

Advantages:

1. Variations. Due to reshuffling of chromosomes and crossing over, variations appear in almost all characters,
2. Adaptability and Evolution. Variations help the organisms to develop adaptability to changes in environment. Their accumulation can also lead to formation of new species.

Question 79.
Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement. (CBSE A.I. 2017)
Answer:
Reproduction is essential for

1. Perpetuation or continuation of species
2. Replacement of dead individuals and maintaining the organisation in population.
3. Introduction of variations for better adaptability and survival.

Question 80.
What is vegetative propagation ? State two advantages and two disadvantages of this method.
(CBSE A.I. 2017)
Answer:
Definition: Vegetative propagation is the formation of new plants by using vegetative parts of a parent plant as propagules e.g., stem (Sugarcane, Bougainvillea, Potato), root (Sweet Potato, Dahlia), leaf (Bryophyllum), bud (Agave).
Advantages:

1. It is the only known method of multiplication of seedless plants like Banana and Sugarcane.
2. It is a quicker method as vegetatively reproduced plants bear flowers and fruits earlier than plants raised through seeds.
3. All the individual plants are clones of one another and their parent so that the crop is genetically uniform.
4. Good quality of a variety can be maintained indefinitely.

Disadvantages:

1. There is little adaptability to changes in envrionment.
2. Diseases contracted by a parent spread to all the daughters.

Question 81.
List three techniques that have been developed to prevent pregnancy. Which one of these techniques is not meant for males ? How does the use of these techniques have a direct impact on the health and prosperity of a family. (CBSE A.I. 2017)
Answer:
(a) Contraceptive Techniques: Barrier methods, Hormonal methods, Surgical methods.
(b) Not Meant for Males. Hormonal methods.
(c) Impact.

1. Enjoying a good reproductive health.
2. Protecting from sexually transmitted diseases.
3. Restricting the number of children.
4. Spacing the birth of children so as to properly look after them, provide them proper education without depleting the resources of the family.
5. Controlling population.

Question 82.
How do variations arise in organisms ? “Variation is useful for survival of species”, justify this statement with the help of an example. )CBSE Foreign 2017)
Answer:
(a) Variations. Variations are differences found in morphological, physiological and other traits of individuals
belonging to the same organism, race or family. They develop due to

1. Faulty DNA replication
2. Crossing over
3. Chance separation of chromosomes during meiosis and chance combination during fertilization.

(b) Variation for Survival. Some of the variations function as pre-adaptations. They help in survival under adverse conditions. Rise in temperature of temperate waters would kill all bacteria except some which had a variation to tolerate heat. Such bacteria will survive and multiply.

Question 83.
What is regeneration ? Give on example of an organism that shows this process and one organism that does not. Why does regeneration not occur in the latter ? (CBSE Foreign 2017)
Answer:
Regeneration: It is ability of an individual to form lost or broken parts, sometimes the entire individual I from a piece of the parent body. The ability to form the whole individual from a piece of parent body is
found only in simple animals like Hydra and Planaria. It does not occur in complex organisms like humans, birds, lizards etc. Here regeneration is limited to repair or regeneration of minor parts. It is because the tissues and organs are highly differentiated in complex animals.
Examples: Planaria, Hydra. Organisms Not Showing Regeneration. Amoeba, Rhizopus, Banana. The reason for absence of regeneration is non-availability of reserve cells and incapability of differentiated cells to dedifferentiate.

Question 84.
What is contraception ? Name any two methods. How does the use of these methods have a direct effect on the health and prosperity of a family ? State any three points. (CBSE Foreign 2017)
Answer:
Contraception. It is technique or mechanism to deliberately prevent conception or impregnation or pregnancy.
Techniques. Barrier methods, Hormonal methods, Surgical methods.
Impact:

1. Enjoying a good reproductive health.
2. Protecting from sexually transmitted diseases.
3. Restricting the number of children.
4. Spacing the birth of children so as to properly look after them, provide them proper education without depleting the resources of the family.
5. Controlling population.

Question 85.
What is placenta ? Describe its two major functions. (CBSE Foreign 2017)
Answer:

Placenta: It is a special double layered, spongy tissue connection between the foetus and uternine wall found in pregnant females. It has finger-like outgrowths or villi which are in contact with blood sinuses present in the uterine wall.
Role:

1. Attachment: Placenta attaches the foetus to uterine wall.
2. Villi: Placenta has finger-like outgrowths or villi which develop a large surface area for fixation and absorption.
3. Nutrients: Placenta picks up nutrients from mother’s blood and passes it to the blood of the foetus.
4. Waste Products: Waste products produced by the foetus passes out through the placenta into mother’s blood.
5. Gases: Foetus obtains oxygen supply from mother’s blood and eliminates carbon dioxide through placenta.

Question 86.
Name the two types of mammalian gametes. How are they different from each other. Name the type of resproduction they are involved in. Write the advantage of this type of reproduction. (CBSE Foreign 2017)
Answer:
Mammalian Gametes. Male-Sperm, Female-Ovum.
Differences: Male gamete or sperm is smaller, dart-like motile gamete with scanty amount of food reserve. Female gamete or ovum is larger, rounded, non-motile gamete with a good amount of reserve food. The difference helps the ovum to get loaded with cytoplasmic contents and allow the sperm to swim freely upto the ovum.
Advantages:

1. Variations. Due to reshuffling of chromosomes and crossing over, variations appear in almost all characters,
2. Adaptability and Evolution. Variations help the organisms to develop adaptability to changes in environment. Their accumulation can also lead to formation of new species.

Long Answer Questions (5 Marks Each)

Question 1.
Draw the diagram of a flower to show its male and female reproductive parts. Label the following in it ;

1. Ovary
2. Anther
3. Filament
4. Stigma.

What is the function of anther ? How does fusion of male and female gametes take place in plants ?
Answer:

Function of Anther. To produce haploid pollen grains which on growth form pollen tubes, each containing two male gametes.
Fusion of Male and Female Gametes. On germination over stigma, a pollen grain forms a long pollen tube carrying two male gametes. Pollen tube enters an ovule and bursts open in the embryo sac. One male gamete fuses with the egg to form diploid zygote. It is generative fertilization. The second male gamete fuses with diploid secondary nucleus of central cell to form triploid primary endosperm cell. It is vegetative fertilization. The phenomenon of two male gametes fusing with different cells in the same embryo sac to produce two different structures is called double fertilization.

Question 2.
(a) Draw a diagram showing germination of pollen on stigma of a flower.
(b) Label pollen grain, male germ cells, pollen tube, stigma, ovary and female germ cell in the above diagram.
(c) How is zygote formed ? (CBSE Delhi 2008 Ç, CCE 2012)
Answer:
(d)

(b) Label as required.
(c) Zygote or first diploid cell is formed by fusion of a male gamete (brought by pollen tube) with oosphere or egg inside the embryo sac.

Question 3.
Draw a longitudinal section of a flower and label the following parts :

1. Part that produces pollen grains,
2. Part that transfers male gametes to the female gametes.
3. Part that is sticky to trap pollen grain,
4. Part that develops into a fruit. (CBSE A.I. 2010)

Answer:

Labelling,

1. Anther—part that produces pollen grains.
2. Style—part that transfers male gametes to female gametes, by providing growth medium to pollen tubes.
3. Stigma—part that is sticky to trap pollen grain.
4. Ovary—part that develops into a fruit.

Question 4.
(a) Explain the role of placenta in the development of human embryo.
(b) Give example of two bacterial and two viral sexually transmitted diseases. Name the most effective contraceptive which prevents spread of such diseases. (CBSE A.I. 2010, CCE 2015)
Answer:
(a) Role of Placenta:

1. Attachment: Placenta attaches the foetus to uterine wall.
2. Villi: Placenta has finger-like outgrowths or villi which develop a large surface area for fixation and absorption.
3. Nutrients: Placenta picks up nutrients from mother’s blood and passes it to the blood of the foetus.
4. Waste Products: Waste products produced by the foetus passes out through the placenta into mother’s blood.
5. Gases: Foetus obtains oxygen supply from mother’s blood and eliminates carbon dioxide through placenta.

(b) Bacterial STDs:

1. Gonorrhoea caused by Neisseria gonorrhoea.
2. Syphilis caused by Treponema pallidum.

Viral STDs:

1. Genital warts by Human Papilloma Virus (HPV).
2. AIDS caused by Human Immunodeficiency Virus (HIV).

Effective Contraceptive. Condom (mechanical barrier).

Question 5.
(a) Differentiate between germination and fertilization.
(b) Differentiate between pollen and ovule
(c) What happens to the following parts after fertilization

1. Ovum
2. Ovary
3. Ovule
4. Sepals and petals.
   (CCE 2011)

Answer:
(a) Germination is the growth of contents of a propagule as the formation of seedling from a seed. Fertilization is fusion of haploid male and female gametes to produce a diploid zygote.
(b) Pollen grain is a haploid structure that grows to form male gametophyte having two male gametes in plants. Ovule is diploid structure in which haploid megaspore produces the female gometophyte or embryo sac having a single female gamete or oosphere.
(c) After fertilization :

1. Ovum forms zygote from which embryo develops,
2. Ovary forms fruit.
3. Ovule produces seed,
4. Sepals and petals shrivel and fall off. In some sepals may persist.

Question 6.
(a) Draw a neat diagram of the reproductive system of a human female and label the following :

1. Reproductive part that produces female hormone,
2. Site of fertilization.
3. Organ where growth and development of the embryo takes place,
4. Entry of sperms.

(b) How does the growing embryo meet with its nutritional requirements ?
(c) What happens if the ovum is not fertilized ?
(d) Mention a contraceptive method that can be used by the human female. (CCE 2011, 2012)
Answer:
(a)

1. Ovary
2. Fallopian tube
3. Uterus
4. Vagina.

(b) Growing embryo obtains nourishment from uterus with the help of a special structure called placenta.
(c) Non-fertilization of ovum later leads to sloughing off the glandular part of the uterine wall and coming out of vagina with blood and mucus collectively called menstrual fluid.
(d) Oral pill/ diaphragm.

Question 7.
(a) Give the function of

1. Stigma
2. Pollen tube,

(b) List two changes observed in the body of a female during puberty,
(c) State in brief the formation of seed in a flower. (CCE 2011)
Answer:
(a)

1. Stigma. Reception of pollen grains and providing nutrients to pollen grains for their germination
2. Pollen Tube. Carrying of male gametes to inside the ovule for fertilization.

(b)

1. Increase in size of breasts and darkening of skin at the base of nipples,
2. Broadening of pelvis and beginning of menstruation.

(c) In a fertilized ovule, embryo grows till it is fully formed. Food is stored either in embryo or in endosperm. The integument of the ovule gets transformed into impermeable seed coat or testa. This changes the ovule into a seed.

Question 8.
(i)

1. Production of sperm
2. Gland which provides fluid
3. Provides low temperature for formation of sperms
4. Common passage for sperms and urine.

(ii) Name a sexually transmitted disease and a method to avoid it.
(iii) State any two changes seen in boys at the time of puberty. (CCE 2011)
Answer:
(i)

1. Testis
2. Prostate gland and seminal vesicles,
3. Scrotum
4. Urethra.

(ii) Gonorrhoea, syphilis (bacterial), warts, HIV (viral). Use of condoms can prevent transmission of infection from infected person to healthy person.
(iii) Development of hair on face, broadening of shoulders and development of larynx with low pitched cracking voice.

Question 9.
(a) Colonies of Yeast fail to multiply in water but multiply in sugar solution. Give one reason for this,
(b) How will an organism he benefitted if it reproduces through spores ?
(c) How is regeneration different from fragmentation ? (CCE 2011)
Answer:
(a) Yeast is heterotrophic. It obtains its nourishment from outside. Plain water cannot provide nourishment to yeast while sugar solution can do so. Therefore, Yeast multiplies in sugar solution and not in plain water.
(b) The parents are diploid (2n) as each of them has two sets of chromosomes (DNAs). They form haploid (In) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes (DNAs). During fertilization, one male gamete fuses with one female gamete. It restores the diploid (2n) chromosome/DNA number in the offspring that is formed from fusion product or zygote (2n).
(c) Regeneration is the ability of an individual to form lost or broken part, sometimes the entire individual from a piece of parent body, e.g., Planaria. Fragmentation is the breaking of the individual into two or more pieces, with each piece growing to form the mature individual, e.g, Spirogyra.

Question 10.
(a) State any three advantages of sexual reproduction over asexual reproduction,
(b) Explain what happens to the egg once it gets fertilized in human female. (CCE 2011, 2013)
Answer:
(a) Advantages of Sexual Reproduction,

1. Due to reshuffling of chromosomes and crossing over, sexual reproduction produces variations in alomost all characters,
2. Sexual reproduction maintains as well as improves vigour and vitality of the individuals,
3. Variability and vitality are helpful to organisms in better adaptability to environment.

(b) Fertilized egg undergoes cleavage forming first a morula and then blastocyst. Blastocyst descends into uterus. With the help of villi, it gets implanted in the wall of uterus. The contact region grows into a disc shaped tissue called placenta. Blastocyst undergoes further development and forms foetus. The foetus remains attached to placenta by means of an umbilical cord. Placenta provides attachment and nourishment to foetus. It also takes away waste products of embryo. Total period required by embryonic development is called gestation period. It is 270 days (40 weeks or 280 days from the date of last menstruation) . The fully formed foetus or embryo is delivered. The process is called parturition.

Question 11.
(a) Name a plant in which vegetative propagation takes place by leaves,
(b) Write causal organism of the following diseases : (t) Warts (zz) Syphilis
(c) Name part of female reproductive system which is ligated to avoid fertilization.
(d) Which device prevents implantation by irritating the lining of uterus ?
(e) What could be the possible reason for declining female sex ratio in our country. Suggest two measures to achieve 1 : 1 ratio.
Answer:
(a) Bryophyllum.
(b)

1. Warts — Virus (Human Papilloma Virus or HPV).
2. Syphilis —Bacterium ( Treponema pallidum).

(c) Fallopian tubes
(d) Intrauterine device like copper-T.
(e)

1. Female foeticide
2. Measures. (I) Banning prenatal sex test (II) Giving inducement and facilities for the female child.

Question 12.
(a) List any two reasons for the appearance of variations among the progeny formed by sexual reproduction

(b)

1. Name the parts maked ‘1’ and ‘2’ in the diagram
2. How does ‘1’ reach ‘2’ ?
3. What happens to part ‘4’ after fertilization ?
4. Mention the importance of part 3. (CCE 2011)

Answer:
(a) Variations appear in the progeny of sexually reproducing organisms due to

1. Random separation and coming together of chromosomes during gamete formation and gamete fusion
2. Crossing over and mutations.
3. Coming together of chromosomes of the parents.

(b)

1. ‘1’— pollen grain.
   ‘2’ — stigma,
2. Through pollination,
3. Formation of fruit,
4. It takes the male gametes to the inside of ovule.

Question 13.
(a) Draw the diagram of a flower to show its male and female reproductive parts.
Label the following parts on it :

1. Ovary
2. Anther
3. Filament
4. Stigma.

(b) How does fusion of male and female gametes takes place in plants ?
(c) List in tabular form any two differences between a male gamete and a female gamete. (CCE 2011)
Answer:
(a)

(b) After passing into ovule, the pollen tube enters the embryo sac through one of the synergids. It then bursts open to release its two pale gametes. One male gamete fuses with the female gamete called oosphere. It gives rise to zygote. Zygote grows to form the embryo.
(c)

Male Gamete	Female Gamete
1.   Size: It is generally smaller. 2.   Food: It has little stored food. 3.   Motility: The male gamete is generally motile.	1.     Female gamete is generally larger. 2.     It contains a lot of stored food. 3.     The female gamete is generally non-motile.

 

Question 14.
(a) Name the parts A, B, C and D in the diagram

(b) Name the parts associated with

1. Fertilization
2. Production of an egg.

(c) What happens to the lining of uterus

1. Before release of fertilized egg
2. If no fertilization occurs,

(d) Name the surgical methods of birth control. (CCE 2011, 2012)
Answer:
(a) (A) — Fallopian tube.
(B) — Ovary.
(C) — Endometrium.
(D) — Cervix.
(b)

1. Fertilization— Fallopian tube,
2. Production of Egg. Ovary.

(c)

1. Proliferation of endometrium under the influence of estrogen and progesterone.
2. After a few days, endometrial lining breaks. Alongwith mucus and some blood it is passed out as menstruation.

(d) Vasectomy (blockage of vasa deferentia in males) and tubectomy (blockage of fallopian tubes in females).

Question 15.
(a) Draw a diagram to show fertilization in a flowering plant and label on it

1. Stigma
2. Ovary
3. Pollen grain
4. Female germ cell.

(b) Define the term “double fertilization” in plants. After fertilization name the part that develops into

1. Fruit
2. Seed.

(c) How is the mode of reproduction in unicellular organisms different from multicellular organisms ?
(CCE 2011)
Answer:
(a)

(b) Definition: The phenomenon of two male gametes fusing with different cells in the same embryo sac to produce two different structures is called double fertilization.
One male gamete fuses with oosphere (egg) to form diploid zygote. It is called generative fertilization. Zygote grows to form embryo. The second male gamete fuses with diploid secondary nucleus of central cell. It produces a triploid primary endosperm cell. The fusion is called triple fusion or vegetative fertilization. It produces a nutritive tissue called endosperm.
(c) Unicellular organisms can multiply through cell-by-cell division. This is not possible in case of multicellular organisms. Here, special cells and other complex modes of multiplication are found.

Question 16.
(a) How does Hydra reproduce ? Explain in brief with the help of a labelled diagram.
(b) Is fertilization possible without pollination ?
(c) What is copper-T ? In which part of the reproductive system is it placed ?
(d) Describe changes in a flower after fertilization. (CCE 2011)
Answer:
(a) Under favourable conditions Hydra reproduces by budding. A bud develops in the lower half due to proliferation of cells. The bud grows in size. It develops mouth and tentacles and begins to feed itself. The bud now constricts at the base and separates as a new individual.

(b) No. Fertilization cannot occur without the male gamete (brought by germinating pollen grain) coming in contact with female gamete.
(c) Copper—T is an intra-uterine device which is kept inside the uterus causing death of sperms and irritation of endometrial lining so as to prevent implantation.
(d) After fertilization, the non-essential and non-required parts of a flower wither and fall down. Petals and stamens are the first to be shed. Sepals may or may not persist. Style and stigma are also shed in most of the cases. The ovary grows in size and ripens into fruit.

Question 17.
(a) The fertilized ovules also grow in size.  They ripen into seeds. How does reproduction occur in

1. Malaria Parasite
2. Leishmania.

(b) Categorise the following flowers into bisexual and unisexual : Papaya, Watermelon, Hibiscus, Mustard.
(c) State in brief the function of urethra in man. (CCE 2011)
Answer:
(a)

1. Malaria Parasite: Multiple fission (asexual). Sexual reproduction also occurs,
2. Leishmania: Longitudinal binary fission (asexual). Sexual reproduction also’occurs.

(b) Bisexual: Hibiscus, Mustard. Unisexual. Papaya, Watermelon
(c) Urethra: Passage of urine (both in males and females), passage of semen in males.

Question 18.
(a) Draw a well labelled diagram of human male reproductive system,
(b) When does ovulation occur during the menstrual cycle in a normal healthy woman,
(c) What is menopause ? (CCE 2012)
Answer:
(a)


(b) Timing of Ovulation: 13th or 14th day of menstrual cycle.
(c) Menopause: It is permanent stoppage of menstruation in women which generally occurs between the age ‘ of 45—50 years.

Question 19.
(a) What is meant by asexual reproduction ? List four different methods of asexual reproduction.
(£) Describe in brief binary fission in Amoeba. (CCE 2012)
Answer:
(a) Asexual Reproduction. It is mode of reproduction in which a part of a single parent gives rise to a new individual without fertilisation or fusion of gametes.
Methods,

1. Fission (binary and multiple)
2. Budding.
3. Fragmentation,
4. Spore formation.

(b) Binary Fission in Amoeba. It can occur in any plane. Pseudopodia are withdrawn. The nucleus elongates and then divides into two. The cytoplasm also cleaves. It produces two daughters, each with a single nucleus.

Question 20.
(a) Draw a labelled diagram of human male reproductive system.
(b) Mention the function of testes. Where are they located ? (CCE 2012)
Answer:
(a)


(b) Function of Testes. Formation of sperms and secretion of male sex hormone testosterone.
Location. The two testes lie in the two chambers of scrotum which hangs from the abdomen behind the penis.

Question 21.
(a) How do the following contraceptives prevent pregnancy :

1. Oral pills
2. Condom.

(b) Mention the possible misuse of surgical method of birth control by some people. How is this method causing harm to the society ? State the steps taken by the government to prevent this misuse. (CCE 2012)
Answer:
(a)

1. Oral Pills: They prevent ovulation (release of mature ovum from ovary) as they contain progesterone (with or without estrogen).
2. Condom: It is a mechanical method which prevents the entry of sperms in the reproductive tract of the female.

(b) Misuse of Surgical Method. Abortion as a means of termination of unwanted pregnancy has been misused to terminate only female foetus. This has caused a decline in sex ratio which is likely to create social tension. In order to prevent female foeticide, the government has banned prenatal sex determination.

Question 22.
(a) Give an example of a bisexual flower. What is its female reproductive organ known as.
(b) Draw a diagram of its longitudinal section showing the process of germination of pollen on stigma and label the following on it :

1. Male germ cell
2. Female germ cell
3. Ovary
4. Pollen tube.

(c) List any two differences between pollination and fertilisation. (CCE 2012)
Answer:
(a) Bisexual Flower. Mustard, Salvia. Female Reproductive Part. Pistil or carpel.
(b)

(c)

1. Pollination is the transfer of pollen grains from the anthers to the stigma of a flower. Fertilization is the fusion of a male gamete brought by pollen tube with the egg or oosphere of the embryo sac.
2. Pollination is the first physical process of sexual reproduction in seed plants. Fertilization is the later biological process of sexual reproduction.

Question 23.
(a) Female and male germ cells are respectively present in ovary and pollen grains of a flowering plant. Draw a labelled diagram to show germination of pollen on stigma.
(b) Explain post fertilization changes that occur in a flower. (CCE 2012)
Answer:
(a)

1. Female Germ Cell. Oosphere, present in embryo sac part of ovule.
2. Male Germ Cell. Male gamete or sperm formed in germinating pollen grain and taken to embryo sac by pollen tube.
   

(b) Post Fertilization Changes,

1. Zygote forms embryo,
2. Primary endosperm cell produces nutritive tissue called endosperm
3. Integuments. Form seed coats. Ovule is transformed into seed. Ovary is transformed into fruit.
   Sepals, petals and stamens shrivel and fall down. Sepals persist is some plants. Style and stigma also fall down.

Question 24.
(a) Draw diagram of a germinating seed and label

1. Part that gives rise to shoot system,
2. Part that gives rise to root system,
3. Part that contains stored food.

(b) How do Potato and Bryophyllum plants reproduce vegetatively ? (CCE 2012)
Answer:
(a)

label:

1. Plumule
2. Radicle
3. Cotyledon.

(b)

1. Potato is multiplied vegetatively by planting pieces of tubers, containing one or more eyes (depression with buds),
2. Bryophyllum is multiplied by placing a mature leaf over moist soil when several plantlets will be formed from growth of buds present in marginal notches.

Question 25.
(a) List the sexually transmitted diseases.
(b) Mention any one method that should be adopted both by male and female for safe sex. (CCE 2012)
Answer:
(a) Gonorrhoea, syphilis, genital warts, AIDS.
(b) Wearing of condoms (males) or contraceptive diaphragms (females) protect both males and females from getting sexually transmitted diseases.

Question 26.
(a) Draw labelled diagram of human male reproductive system.
(b) State the reason why testes are located outside abdominal cavity.
(c) Name the hormone secreted by testes.
(d) Write two glands found in male reproductive pathway and specify their roles. (CCE 2012)
Answer:
(a)


(b)

1. Scrotum not only protects the testes but also acts as a thermoregulator by changing position of the testes.
2. It keeps the temperature of testes 1 -3° C below that of the body. A lower temperature is essential for development of sperms.

(c) Testosterone:

1. Regulating sperm formation,
2. Puberty changes in males,
3. Maintenance of male secondary organs and traits.

(d) Two Glands: A pair of seminal vesicles and prostate gland.
Seminal Vesicles: They secrete 60-70% of semen plasma that is alkaline and viscous having fructose (for nourishing the sperms), fibrinogen, proteins and prostaglandins. Prostaglandins cause movements in the genital tract of the female. Sperms are also activated by secretion of seminal vesicles.
Prostate Gland: It produces 20-30% of semen plasma. The secretion is alkaline and viscous. It has clotting enzyme and chemical essential for sperm activity.

Question 27.
(a) Draw a neat diagram of human female reproductive system and label

1. Oviduct
2. Ovary
3. Uterus
4. Cervix.

(b) Mention the function of uterus and oviduct. (CCE 2012)
Answer:
(a)


(b)

1. Uterus,
   1. It is seat of implantation of embryo.
   2. Uterus provides protection to embryo,
   3. It supplies nutrients to the foetus and takes away its waste products.
2. Oviduct (Fallopian Tube),
   1. It is passageway for ova.
   2. It is the site of fertilization of ovum.

Question 28.
(a) Give reason :

1. Wind acts as a pollinating agent
2. Variation is essential and beneficial to a species.
3. Use of condoms prevents pregnancy.

(b) What is menstruation ? Explain why it occurs.
How does embryo get nutrition in mother’s womb. (CCE 2012)
Answer:
(a)

1. Wind picks up the pollen grains of dehisced anthers and disperses the same. Stigmas are often feathery or sticky to retain pollen grains striking against them. Wind pollination is called anemophily.
2. Variations function as preadaptations which help the species to survive in changed environmental conditions.
3. Condoms are mechanical barriers which do not allow the sperms to pass into genital tract of the female. Therefore, pregnancy is prevented.

(b) Menstruation:

1. It is discharge of blood, mucus and broken pieces of endometrial lining in reproductively active females which occurs for 3-5 days at regular intervals of 28 days (lunar month). It occurs in response to non-fertilization of ovum and non-availability of progesterone hormone.
2. Nutrition to Embryo: Embryo gets nourishment from mother’s body with the help of placenta through a cord called umbilical cord. Placenta contains many finger-like villi from the chorion covering of the embryo. They occur in contact with blood sinuses of the mother present in the endometrial lining of uterus. All nutrients (glucose, amino acids, vitamins, etc.) diffuse from mother’s blood into villi and from there to embryo through the umbilical cord.

Question 29.
With the help of suitable diagrams explain how reproduction occurs in Hydra and Planaria. Also name the process involved. (CCE 2012)
Answer:
Reproduction, in Hydra: Some reserve cells present in the lower half of Hydra begin to divide due to some internal or external stimulus. They form a cellular mound which grows into a bud. Soon the bud develops a mouth and tentacles. It makes the bud nutritionally independent. The bud constricts from base and separates as a new individual.

Reproducdon in Planaria. It occurs by regeneration. Due to passage through narrow spaces, Planaria often gets broken into two or more pieces. The cut ends of the pieces show proliferation of cells. The newly formed cells undergo differentiation and form missing parts to regenerate the whole animal.

Question 30.
Write two causes of human population explosion. Explain with the help of suitable examples, how this explosion can be checked. (CCE 2013)
Answer:
Population explosion is the rapid rise in human population.
Causes:

1. Decrease in death rate,
2. Longer life span. Both are due to progressively improving health care facilities.

Check: Population explosion can be checked only through fertility control or family planning.
This can be achieved through

1. Education. There is an inverse ratio between education and population growth.
2. Population Education. It is imparting knowledge to public about the effects of excessive population, advantages of small families and means to achieve it.
3. Marriageable Age. Number of births is reduced if young persons marry late. Gainful employment and higher social status of women also reduce birth rate.
4. Easy Availability of Birth Control Means. This will reduce reluctance on the part of eligible couples to adopt family planning measures.

Question 31.
What is pollination ? How does it occur in plants ? How does pollination lead to fertilization ? Explain.
(CCE 2013)
Answer:
Pollination: It is the transfer of pollen grains from anther to the stigma.
Occurrence: Pollination can occur through the agency of air (anemophily), water (hydrophily), insects (entomophily) as well as other animals and mechanical disturbance (self pollination).
Fertilization: After falling on a compatible stigma, the pollen grain absorbs water and nutrients. It gives out pollen tube. The pollen tube carries two male gametes. It grows through style, reaches ovary, enters an ovule and bursts open into its embryo sac. One male gamete fuses with the egg to produce diploid zygote. It is fertilization. The zygote later forms embryo. There is a second fertilization in flower bearing plants—the second male gamete Fuses with central cell of embryo sac to form nutritive tissue endosperm. It is required for nourishment of embryo.

Question 32.
(a) List three distinguishing features between sexual and asexual types of reproduction.
(b) Explain why variations are observed in the offspring of sexually reproducing organisms. (CCE 2013)
Answer:
(a)

1. Parents: Sexual reproduction is generally biparental while asexual reproduction is monoparental
2. Gametes: Sexual reproduction involves the formation and fusion of gametes. Gametes have no role in asexual reproduction.
3.  Meiosis: Meiosis occurs once in sexual reproduction. All divisions are mitotic in asexual reproduction.

(b)

1. Chance separation of chromosomes during meiosis required for gamete formation,
2. Crossing over during meiosis.
3. Chance coming together of chromosomes during fertilization,
4. Mutations or mistakes during DNA replication.

Question 33.
(a) Identify A, B and C in given diagram and write their functions,

(b) Mention the role of gametes and zygote in sexually reproducing organisms. (CCE 2013, 2015)
Answer:
(a)
A-stigma: Reception of pollen grains and providing nutrients to pollen grains for their germination
B-pollen tube: Carrying of male gametes to inside the ovule for fertilization.
C-egg: Forms zygote and then embryo after fertilization.
(b) Gamete: It is haploid sex cell that brings traits in pure form from its parent for incorporation in the offspring. Zygote. Forms embryo.

Question 34.
(a) Draw a sectional view of human female reproductive system and label the following parts :
(b)

1. Where development of egg occurs
2. Where fertilization takes place.

Answer:
(a)


Label

1. Ovary
2. Fallopian tube.

(b)

1. Endometrium thickens, becomes glandular and highly vascular. The contact region between embryo and uterine wall grows into placenta. Placenta helps the embryo in obtaining nourishment and oxygen from blood sinuses of the uterus. It also helps in transfer of wastes from embryo to the blood of the mother.
2. Glands present in the mucosa of uterine endometrium begin to degenerate. This sloughs off the endometrial lining, releasing a lot of mucus and blood. It is called menstruation. Menstruation lasts for 3-5 days.

Question 35.
(a) Write the function of placenta in human females,
(b) List four ways of preventing pregnancy. State two advantages of using such preventive methods. (CCE 2013)
Answer:
(a) Placenta: It is a special double layered, spongy tissue connection between the foetus and uternine wall found in pregnant females. It has finger-like outgrowths or villi which are in contact with blood sinuses present in the uterine wall.
Role:

1. Attachment: Placenta attaches the foetus to uterine wall.
2. Villi: Placenta has finger-like outgrowths or villi which develop a large surface area for fixation and absorption.
3. Nutrients: Placenta picks up nutrients from mother’s blood and passes it to the blood of the foetus.
4. Waste Products: Waste products produced by the foetus passes out through the placenta into mother’s blood.
5. Gases: Foetus obtains oxygen supply from mother’s blood and eliminates carbon dioxide through placenta.

(b) Methods of Contraception:

1. Mechanical Barriers like condoms, cervical cap, diaphragm.
2. Oral Contraceptives or oral pills like Mala D, Saheli
3. Intrauterine Contraceptive Devices (IUCD) like loop, bow, Cu-T.
4. Surgical Methods like vasectomy in males and tubectomy in females.

Question 36.
(a) Name the respective part of human female reproductive system

1. that produces eggs
2. where fusion of egg and sperm takes place and
3. where zygote gets implanted.

(b) Describe in brief what happens to the zygote after it gets implanted. (CCE 2014)
Answer:
(a)

1. Ovary
2. Fallopian tube (isthmus)
3. Uterus.

(b) Zygote/blastocyst after implantation grows to form embryo/foetus. The region of implantation forms placenta. The foetus remains attached to placenta by means of umbilical cord. Through placenta, embryo is in contact with blood sinuses of the uterus for obtaining nutrients and elimination of wastes. The fully formed foetus undergoes parturition.

Question 37.
(a) Give an example each of a unisexual and a bisexual flower.
(b) Mention the changes a flower undergoes after fertilization.
How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals ? (CCE 2014)
Answer:
(a) Unisexual Flowers: Papaya.
Bisexual Flower: Mustard.
(b) DNA Amount: The parents are diploid (2n) as each of them has two sets of chromosomes (DNAs). They form haploid (In) male and female gametes through the process of meiosis. The haploid gametes have one set of chromosomes (DNAs). During fertilization, one male gamete fuses with one female gamete. It restores the diploid (2n) chromosome/DNA number in the offspring that is formed from fusion product or zygote (2n).

Question 38.
(a) Write the name of the human male reproductive organ that produces sperms and secretes a hormone.
Describe the changes the uterus undergoes

1. to receive the zygote
2. if zygote is not formed.
3. Name the hormone secreted and state its function.

(b) Write the site of fertilization and the part where the zygote gets implanted in the human female.
(c) State, in brief, how an embryo gets its nourishment inside the mother’s body. (CCE 2014, 2015)
Answer:
(a) Testis. Hormone. Testosterone.
Function of Testosterone

1. Regulates sperm formation
2. Brings about puberty changes in males.
3. Maintains male secondary organs and traits.

(b) Site of Fertilization. Isthmus part of fallopian tube. Site of Implantation. Uterus.
(c) Nourishment of Embryo: Embryo gets nourishment from mother’s body with the help of placenta through a cord called umbilical cord. Placenta contains many finger-like villi from the chorion covering of the embryo. They occur in contact with blood sinuses of the mother present in the endometrial lining of uterus. All nutrients (glucose, amino acids, vitamins, etc.) diffuse from mother’s blood into villi and from there to embryo through the umbilical cord.

Question 39.
(a) Define fragmentation and regeneration,
(b) Can these two methods equated to be the same ? Answer with reason
(c) Give an example each of the organisms using the above methods. (CCE 2014)
Answer:
(a) Fragmentation. It is breaking of an individual into two or more pieces with each piece growing to form the mature individual.
Regeneration. It is the ability of an individual to form lost or broken part, sometimes the whole individual.
(b) The two are not similar. Regeneration involves dedifferentiation, proliferation and differentiation to form lost parts. Fragmentation produces pieces where cells continue to divide resulting in growth of new individual. A repair is not involved.
(c) Regeneration. Hydra, Planaria. Fragmentation. Spirogyra, Marchantia.

Question 40.
Define the following processes :
(a) Fertilization
(b) Vegetative propagation
(c) Menstruation
(d) Regeneration
(e) Binary fission.
Answer:
(a) Fertilization: The union of male gamete (sperm) with the female gamete (ovum) to form a diploid zygote is called fertilization.
(b) Vegetative Propagation: It is the formation of new plants from vegetative parts (e.g., stem, leaf, root, bud) of a parent plant.
(c) Menstruation: It is discharge of blood, mucus and broken pieces of endometrial lining in reproductively active females which occurs for 3-5 days at regular intervals of 28 days (lunar month). It occurs in response to non-fertilization of ovum and non-availability of progesterone hormone.
(d) Regeneration: It is ability of an individual to form lost or broken parts, sometimes the entire individual I from a piece of the parent body. The ability to form the whole individual from a piece of parent body is found only in simple animals like Hydra and Planaria. It does not occur in complex organisms like humans, birds, lizards etc. Here regeneration is limited to repair or regeneration of minor parts. It is because the tissues and organs are highly differentiated in complex animals.

Question 41.
(a) Name the parts labelled A, B, C and D in the diagram.

(b) What is pollination ? State its significance.
(c) How does fertilization occur in flowers ? Name the parts of the flower that develop into

1. seed and
2. fruit after fertilization. (CCE 2014)

Answer:
(a) A—Pollen grain.
B—Pollen tube.
C—ovary.
D—Egg/oosphere.
(b) Pollination. The transfer of pollen grains from anther to the stigma of a flower is called pollination.
Singificance. It carries the immobile pollen grains to the stigma for formation of male gametophyte and fertilization.
(c) After falling on a suitable stigma the pollen absorbs water and nutrients. It produces a pollen tube that grows through the style and reaches the ovary. Its tip contains a tube nucleus and two male gametes. The pollen tube enters an ovule, strikes against one synergid of the embryo sac and bursts open to release its contents. One male gamete fuses with the egg to form zygote while the other fuses with secondary nucleus to produce primary endosperm nucleus.

1. Seed—ovule,
2. Fruit—ovary.

Question 42.
(a) Identify the leaf shown.

(b) Name the method used by the above leaf for reproduction.
(c) Give three advantages for the method used.
(d) Give two examples of plants which can be grown by this method.
(CCE 2015)
Answer:
(a) Bryophyllum
(b) Vegetative propagation
(c)

1. It is quicker method of propagation.
2. It gives rise to a genetically uniform propagation.
3. Good qualities of a variety can be maintained indefinitely.

(d) Sugarcane, Bougainvillea.

Question 43.
Justify the following statements :
(a) Variation is beneficial for the species over a period of time.
(b) New offspring produced are similar to their parents, but not identical
(c) Binary fission is different in Amoeba and Leishmania.
Answer:
a) Many of the variations are pre-adaptations which have no immediate benefit to the individuals. However, they remain in the population. Whenever, environment undergoes a drastic change, the pre-adaptations present in some members of the population allow the latter to survive, grow and regain its former size. Therefore, it is not necessary that variations are beneficial to individuals developing them but can prove useful to the species.
(b) New offspring are similar to their parents because they have obtained the genetic traits from the same. They are, however, not identical because of chance separation, chance combination of chromosomes and recombination of genes due to crossing over.
(c) In Amoeba, binary fission can occur in any plane. In Leishmania the plane of division is vertical.

Question 44.
Explain what happens when :
(a) Testosterone is released in males
(b) Pollen grain falls on the stigma of the flower,
(e) Egg fuses with sperm cell,
(d) Planaria is cut into many pieces,
(e) Buds are formed at the notches of Bryophyllum leaf. (CCE 2015)
Answer:
(a) Testosterone,

1. Regulates formation of sperms,
2. Puberty changes in boys.
3. Maintenance of secondary sexual characters in males.

(b) Pollen Grain. If pollen grain and stigma are compatible, the pollen grain absorbs water and nutrients from the stigma. It germinates and forms a pollen tube. Pollen tube passes into stigma and then style for reaching the ovary.
(c) Egg Fuses with Sperm Cell. The act is called fertilization. It produces a diploid zygote which later on grows into embryo.
(d) Cutting of Planaria. Each piece begins to regenerate, anterior end forms the anterior body parts, while posterior end gives rise to posterior body parts. Regeneration occurs with the help of stem cells and dedifferentiated cells (from differented ones).
(e) Bryophyllum Leaf. Buds present in the marginal notches of Bryophyllum leaf sprout and produce plantlets under suitable conditions. They help in vegetative multiplication.

Question 45.
Differentiate between the following :
(a) Pollen tube and style,
(b) Fission in Amoeba and Plasmodium,
(c) Fragmentation and Regeneration,
(d) Bud of Hydra and Bryophyllum.
(e) Vegetative propagation and spore formation. (CCE 2015)
Answer:
(a) Pollen Tube and Style: Pollen tube is an outgrowth of pollen grain meant for carrying the male gametes to ovule. Style is a stalk-like structure of carpel (= pistil) that is meant for lifting the stigma above the level of ovary.
(b) Fission in Amoeba and Plasmodium: Under favourable conditions Amoeba multiplies by binary fission while Plasmodium multiplies by multiple fission.
(c) Fragmentation and Regeneration :
Fragmentation: It is breaking of an individual into two or more pieces with each piece growing to form the mature individual.
Regeneration: It is the ability of an individual to form lost or broken part, sometimes the whole individual.(d) Bud of Hydra and Bud of Bryophyllum. In Hydra, bud is an outgrowth of the body which gets transformed into new animal that separates to lead an independent life. In Bryophyllum buds develop from the notches of the leaf. After falling on ground, the buds sprout and from plantlets.
(e) Vegetative Propagation and Spore Formation: In vegetative propagation new plants develop from specialised or unspecialised multicellular parts of the parent plant that function as propagules, e.g., Bryophyllum. Sugarcane. In spore formation, the individual parent produces unicellular reproductive bodies that get dispersed and form new individuals on germination, e.g, Rhizopus.

Question 46.
(a) Write the functions of the following parts in human female resproductive system :

1. Ovary
2. Oviduct
3. Uterus.

(b) Describe the structure and function of placenta. (CBSE Delhi 2016, A.I. 2017)
Answer:
(a)

1. Ovary. Formation of ova and secretion of hormones, estrogen and progesterone.
2. Fallopian Tube. Passage of ovum, site for fertilization.
3. Uterus. Implantation and nourishment of embryo.

(b) Placenta: It is a special double layered, spongy tissue connection between the foetus and uternine wall found in pregnant females. It has finger-like outgrowths or villi which are in contact with blood sinuses present in the uterine wall.
Role:

1. Attachment: Placenta attaches the foetus to uterine wall.
2. Villi: Placenta has finger-like outgrowths or villi which develop a large surface area for fixation and absorption.
3. Nutrients: Placenta picks up nutrients from mother’s blood and passes it to the blood of the foetus.
4. Waste Products: Waste products produced by the foetus passes out through the placenta into mother’s blood.
5. Gases: Foetus obtains oxygen supply from mother’s blood and eliminates carbon dioxide through placenta.

Question 47.
(a) What is vegetative propagation ? List with brief explanation three advantages of practising this process for growing some types of plants.
(b) Select two plants from the following which are grown by this process : Banana, Wheat, Mustard, Jasmine,
Gram. (CBSE Foreign 2016)
Answer:
(a) Vegetative propagation is the formation of new plants by using vegetative parts of a parent plant as propagules e.g., stem (Sugarcane, Bougainvillea, Potato), root (Sweet Potato, Dahlia), leaf (Bryophyllum), bud (Agave).
Advantages:

1. It is the only known method of multiplication of seedless plants like Banana and Sugarcane.
2. It is a quicker method as vegetatively reproduced plants bear flowers and fruits earlier than plants raised through seeds.
3. All the individual plants are clones of one another and their parent so that the crop is genetically uniform.
4. Good quality of a variety can be maintained indefinitely.

(b) Banana, Jasmine.

Question 48.
(a) State in brief the function of the following organs in the human female reproductive system : Ovary, Fallopian tube, Uterus.
(i) What is menstruation ? Why does it occur ? (CBSE Foreign 2016)
Answer:
(a)

1. Ovary: Formation of ova and secretion of hormones, estrogen and progesterone.
2. Fallopian Tube: Passage of ovum, site for fertilization.
3. Uterus: Implantation and nourishment of embryo.

(b) Menstruation: 
It is discharge of blood, mucus and broken pieces of endometrial lining in reproductively active females which occurs for 3-5 days at regular intervals of 28 days (lunar month). It occurs in response to non-fertilization of ovum and non-availability of progesterone hormone.

Question 49.
(a) Name the organ that produces sperms as hormone it secretes and write its functions.
(b) Name the parts of the human female reproductive system where fertilisation occurs.
(c) Explain how the develeping embryo gets nourishment inside the mother’s body. (CBSE Delhi 2017)
Answer:
(a) Testes: Hormone produced by testes is testosterone.
Functions of Testosterone:

1. Regulates formation of sperms,
2. Puberty changes in boys.
3. Maintenance of secondary sexual characters in males.

(b) Isthmus part of fallopian tube or oriduct.
(c) Developing embryo obtains nourishment from the mother with the help of placenta. The foetal part of placenta has a number of finger-like outgrowths called villi. Villi are in near contact with blood sinuses representing the maternal part of placenta. There is a large surface area between the two. It helps in easy passage of nutrients from mother’s blood sinuses into blood of the umbilical cord of the foetus.

Question 50.
Give one example each of unisexual and bisexual flowers. Differentiate between the two types of pollination that occur in flowers. What happens when a pollen lands on a suitable stigma ? Write about the events that occur till the seed formation in the ovary. (CBSE Foreign 2017)
Answer:
Unisexual Flower. Papaya, Cucurbita Bisexual Flower. Mustard, Hibiscus.
Types of Pollination. It is of two types, self pollination and cross pollination. Self pollination is the transfer of pollen from the anther to the stigma of the same flower. Cross pollination is the transfer of pollen grains from the anther of one flower to the stigma of another flower.
Events After Pollination. After falling on a suitable stigma, the pollen grain absorbs water and nutrients. It produces a pollen tube. The pollen tube carries two male gametes. It grows through style, reaches the ovary and enters an ovule. Inside the ovle, the tip of pollen tube bursts and releases the two male gametes. One male gamete fuses with the egg to produce diploid zygote. The other male gamete fuses with the diplod central cell of embryo sac to form primary endosperm cell. Zygote grows into embryo. Primary endosperm cell forms nutritive tissue called endosperm. Endosperm may or may not be consumed by the embryo. Integuments of ovule are changed into seed coats. The ovule is transformed into seed (and ovary into fruit).

Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 8 How do Organisms Reproduce? are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 12 Electricity Class 10 Science Important Questions and Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Electricity Class 10 Important Questions and Answers Science Chapter 12

Very Short Answer Questions

Based on Electric Potential and Electric Current

Question 1.
Define electric potential.
Answer:
Electric potential at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point in the electric field.

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
State the relation between work (W), change (q) and electric potential (V).
Answer:
V = W/q.

Question 3.
What is the S.I. unit of electrical potential ? (CBSE 2005, 2012)
Answer:
volt.

Question 4.
Define 1 volt electric potential.
Answer:
Electric potential is said to be 1 volt if 1 Joule of work is done in moving 1 coulomb charge from infinity to a point in the electric field.

Question 5.
Is electric potential a scalar or a vector physical quantity ?
Answer:
Electric potential is a scalar physical quantity.

Question 6.
What is meant by potential difference between two points ? (CBSE 2011)
Answer:
Work done per unit charge in moving a unit positive charge from one point to another point in an electric field is called potential difference between two points.

Question 7.
Name the instrument used to measure the electric potential difference. (CBSE 2011, 2012)
Answer:
Voltmeter.

Question 8.
Write down the relation between the potential difference between two points A and B in a conductor, work done W in moving a unit charge from point B to A and the charge q.
                                                                  Or
State the relation between work, charge and potential difference for an electric circuit.
[CBSE (All India) 2009, 2013]
                                                                 Or
Express work done in an electric field in terms of charge and potential difference. (CBSE 2014)
Answer:

Question 9.
Mention the factor that maintains the flow of charge through a conductor. (CBSE 2013, 2014)
Answer:
Potential difference across the ends of the conductor.

Question 10.
Define electric current.
Answer:
Electric current is defined as the amount of electric charge flowing through any cross-section of a conductor per unit time.

Question 11.
Write down the relation between the electric current I passing in a conductor, change Q flowing in the conductor and time t.
                                                                 Or
Write the relation between coulomb and ampere. (CBSE 2014)
Answer:

Question 12.
State the relation between the current I passing in a conductor, number of electrons (n) flowing through any cross-section of the conductor, magnitude of charge on an electron (e) and time t.
Answer:
I = ne/t.

Question 13.
State SI unit of electric current.
Answer:
ampere (A)

Question 14.
Define 1 ampere electric current.
Answer:
Electric current through a conductor is said to be 1 ampere if 1 coulomb electric charge flows through a cross-section of a conductor in 1 second.

Question 15.
How is the direction of electric current related to the direction of flow of electrons in a wire ?
[CBSE (All India) 2009]
Answer:
The direction of electric current in a wire is just opposite to the direction of flow of electrons in the wire.

Question 16.
Name the instrument used to measure electric current in a circuit. [CBSE (Delhi) 2008, 2011, 2012, 2015]
Answer:
Ammeter.

Question 17.
How is ammeter connected in the circuit to measure electric current ? (CBSE 2011, 2012)
Answer:
Ammeter is connected in series in an electric circuit.

Question 18.
How is voltmeter connected in the circuit to measure electric potential difference ?
Answer:
Voltmeter is connected in parallel across a conductor or resistor in the electric circuit.

Question 19.
Define ohm’s law. [CBSE 2010, 2011, 2012, 2013, 2015]
                                         Or
State the law that gives the relationship between the potential difference (V) across the two ends of a conductor and the current (I) flowing through it. (CBSE 2012)
Answer:
Ohm’s law states that the electric current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and . other physical conditions of the conductor remain the same.

Question 20.
Graph is plotted between the values of potential difference (V) and current (I). What v conclusion do you draw about the relation between V and I from this graph. State this relation in your words. (CBSE 2013)

Answer:
The potential difference (V) is directly proportional to the current (I).

Question 21.
Draw a circuit diagram to establish a relationship between potential difference across the ends of a resistor and current flowing through it. (CBSE 2013)
Answer:

Question 22.
State the formula showing how the current I in a conductor varies with the potential difference V applied across it. [CBSE (Delhi) 2004(S), 2012]
Answer:
V ∝ I or V = IR or I = V/R .

Question 23.
Define electrical resistance of a conductor. (CBSE 2013)
Answer:
It is the property of a conductor to oppose the flow of electric charge through it.
Resistance of a conductor, R = V/I , where V is the potential difference across the conductor and I is the current flowing through the conductor.

Question 24.
State SI unit of resistance. [CBSE (Delhi) 2004(S), 2012]
Answer:
ohm (Ω).

Question 25.
“The resistance of a conductor is IΩ”. What is meant by this statement ? (CBSE 2010, 2011, 2012)
                                               Or
Define 1 ohm resistance. (CBSE 2014)
Answer:
The resistance of a conductor is said to be 1Ω if a potential difference of IV across the ends of the conductor makes a current of 1A to flow through it.

Question 26.
What is the shape of the graph obtained by plotting potential difference applied across a conductor against the current flowing through it ?
Answer:
A straight line passing through the origin and has constant slope.

Question 27.
What is the name the physical quantity which is equal to V/I ?
                                                Or
Name the physical quantity whose unit is volt-ampere.
Answer:
y = R. Therefore, physical quantity is resistance of a conductor.

Question 28.
What does the slope of V-I graph at any point represent ?
Answer:

Therefore, slope of V-I graph represents reciprocal of the resistance of a conductor resistance of a conductor.

Question 29.
What happens to resistance of a conductor when temperature is increased ?
Answer:
Resistance of a conductor increases with the increase in temperature.

Question 30.
The voltage — current (V-I) graph of a metallic circuit at two different
temperature T₁ and T₂ is shown. Which of the two temperatures is higher and why ? (CBSE 2010)
                                                                         Or
The voltage-current (V-I) graph of a metallic conductor at two different temperatures T₁ and T₂ is shown in figure. At which temperature is the resistance higher ? (CBSE 2011, 2012)

Answer:
Slope of I-V graph = resistance of metallic conductor.
Since, slope of I-V graph at temperature T₂ is greater than the slope of I-V graph at temperature T₁, therefore, resistance at T₂ is greater than resistance at T₁ . Since, resistance of a metallic conductor increases with increase in temperature, therefore, T₂ > T₁.

Question 31.
How does the resistance of a wire vary with its cross-section area ?
Answer:
Resistance of a wire is inversely proportional to its cross-sectional area. More is cross-sectional area of a conductor, less is the resistance of the conductor.

Question 32.
State the relation between the resistance R of a conductor, resistivity ρ of a conductor, length l of a conductor and area of cross-section A of the conductor.
                                                      Or
Write an expression for the resistivity of a substance. (CBSE 2015)
Answer:

where R is the resistance, A is the area of cross-section and l is the length of the substance.

Question 33.
What is electrical resistivity ? [CBSE 2010, 2014, 2015]
Answer:
Electrical resistivity of a material is defined as the resistance of an object (made of the material) of unit length and unit area of cross-section.

Question 34.
State SI unit of resistivity. [CBSE (Delhi) 2004 (S), 2014, 2015]
Answer:
ohm-metre (Ω-m).

Question 35.
A wire of resistivity ‘ρ’ is pulled to double its length. What will be its new resistivity ? (CBSE 2010, 2011)
Answer:
New resistivity will also be ‘ρ’ because resistivity of a wire does not depend on its length.

Question 36.
You have a metal, insulator and an alloy. Write these substances in the ascending order of their electrical resistivity.
Answer:
Resistivity of metal < resistivity of alloy < resistivity of insulator.

Based on resistors connected in series and parallel 

Question 37.
n resistance each of R are connected in series in a circuit. What is the total effective resistance of the circuit ?
(CBSE 2010)
Answer:
R_eff = R₁ + R₂ + R₃ + … upto n = nR

Question 38.
n resistors each of resistance R are connected in parallel in an electric circuit. What is the total effective resistance of the circuit ? (CBSE 2010 )
Answer:

Question 39.
n resistors each of resistance R are first connected in series and then in parallel. What is the ratio of the total effective resistance of the circuit in series combination and parallel combination ? (CBSE 2013)
Answer:

Question 40.
You have two metallic wires of resistances 60 and 30. How will you connect these wires to get the effective resistance of 20 ? (CBSE 2010, 2012)
Answer:
In parallel.

Question 41.
Draw a schematic diagram of a circuit consisting of battery of two cells each of 1.5 V, 50 resistor, 100 resistor and 150 resistor and a plug key, all connected in series. [CBSE (All India) 2009, 2011, 2013]
Answer:

Based on heating effect of electric current

Question 42.
What is heating effect of electric current ?
Answer:
The production of heat in a conductor due to the flow of electric current through it is called heating effect of electric current.

Question 43.
Write down the relation between heat produced H in a conductor of resistance R through which current I passes for t seconds.
Answer:
H = I²Rr.

Question 44.
State Joule’s law of heating. (CBSE 2012, 2012, 2013, 2014, 2015)
Answer:
According to Joule’s law of heating, the amount of heat produced in a conductor is

1. directly proportional to the square of electric current passing through the conductor,
2. directly proportional to the resistance of the conductor, and
3. directly proportional to the time for which electric current passes through the conductor.

Question 45.
Write a mathematical expression for Joule’s law of heating. Name one device which works on this principle.
(CBSE 2010, 2015)
Answer:
H = I² Rt. An electric heater and electric bulb work on Joule’s law of heating.

Question 46.
What is meant by the statement that the rating of fuse in a circuit is 5A ?
Answer:
It means maximum current of 5A can pass through the fuse without melting it.

Question 47.
Name the material used for making the filament of a bulb.
Answer:
Tungsten.
on electric energy and electric power

Question 48.
Define electric energy. (CBSE 2013, 2015)
Answer:
It is defined as the work done by a source of electricity to maintain electric current in an electrical circuit.

Question 49.
Define electric power.
Answer:
It is defined as the amount of electric energy consumed in an electric circuit per unit time.

Question 50.
Name the physical quantity expressed as the product of potential difference and electric current.
Answer:
Electric power.

Question 51.
State SI unit of electric power.
Answer:
Volt x ampere (or Watt).

Question 52.
Name the unit used in selling electrical energy to consumers.
                               Or
What is the commercial unit of energy ?
Answer:
Kilowatt hour (kWh).

Question 53.
Which one is having lesser resistance : A 60 W bulb or a 40 W bulb ?
Answer:

Hence, bulb of higher wattage will have less resistance. In other words, resistance of 60W bulb is less than the resistance of 40 W bulb.

Question 54.
What is the difference between kilowatt and kilowatt hour. (CBSE 2012, 2014)
Answer:
Kilowatt is the unit of electric power and kilowatt hour is the commercial unit of electric energy.

Short Answer Questions (2 & 3 Marks)

Based on electric current, ohm’s law and resistance

Question 1.
Define electric current. State and define its SI unit. (CBSE 2012, 2013, 2014, 2015)
Answer:
Electric current is defined as the amount of charge flowing through a cross-section of a conductor in unit time.

SI unit of electric current is ampere (A).
Electric current through a conductor is said to be 1 ampere if one coulomb charge flows through a cross-section of the conductor in one second.

Question 2.
List two differences between a voltmeter and ammeter. (CBSE 2013)
Answer:

Ammeter	Voltmeter
1.    Ammeter measures electric current in the circuit. 2.     Ammeter is connected in series in an electric circuit.	1.     Voltmeter measures the potential difference be­tween two points on a conductor. 2.     Voltmeter is connected in parallel across the ends of a conductor or resistor.

Question 3.
What is an electric circuit ? Distinguish between an open and a closed circuit.
[CBSE (All India) 2009, 2010, 2011]
Answer:
electric circuit:
An electric circuit is a closed conducting path containing a source of electric energy (i.e., a cell or a battery) and a device or element or load (say, an electric bulb) utilizing the electric energy.
The direction of electric current is opposite to the direction of the flow of electrons in the conductor.
Open electric circuit : An electric circuit through which no electric current flows is known as open electric circuit.
The electric circuit shown in figure 10 (A) will be open circuit if the plug of the key is taken out or if the connecting wire breaks from any point.

Closed circuit : An electric circuit through which electric current flows continuously is known as closed circuit (Figure 10 (B)).

Question 4.
What do the following symbols represent in a circuit ? Write the name and one function of each.
(CBSE 2013)

Answer:
(i) It represents a battery. It maintains a potential difference across the circuit element for the flow of current in the circuit.
(ii) It represents an ammeter. Ammeter is used to measure the electric current in the circuit.

Question 5.
What do the following symbols represent in a circuit ? Write the name and one function of each ?
[CBSE 2011, 2012, 2013, 2015]

Answer:
(i) It represents a closed plug key. It is used to make the closed electric circuit.
(ii) It represents a variable resistance. It is used to increase or decrease the electric current in the circuit.
(iii) It represents a voltmeter. It is used to measure the potential difference across a resistor in the circuit.
(iv) It represents a galvanometer. It is used to detect the presence of small current in the circuit.
(v) It represents wire crossing (not connected with each other). The wires are used to connect various components in the circuit.

Question 6.
Express Ohm’s law both by a mathematical formula and by a graph line. (CBSE (Delhi) 2004 (S))
Answer:
Mathematical formula of Ohm’s law is
V = IR
For a graph line,

Question 7.
List the factors on which the resistance of a conductor depends. Write the expression to show the relation of resistance with these factors. (CBSE 2013, 2014)
Answer:
Resistance of a factor depends on its length (l) and area of cross section (A).

Question 8.
What is likely to happen and how it would affect the value of resistance if we pass the current for a longer time ? (CBSE 2014)
Answer:
When current passes through a conductor for a longer time, the conductor is heated due to Joule’s heating effect. Resistance of conductor increases with increase in temperature due to heating effect.

Question 9.
Two wires, one of copper and other of manganin, have equal lengths and equal resistances. Which wire is thicker ? Given that resistivity of copper is lower than that of manganin. (CBSE 2011, 2015)
Answer:

Since l and R of both the wires are same, so A p . Since, resistivity ip) of manganin is higher than that of copper, so manganin wire is thicker than that of copper wire.

Question 10.
Mention the condition under which charge can move in a conductor. Name the device which is used to maintain this condition in an electric circuit. (CBSE 2012, 2013)
Answer:
The ends of the conductor must be maintained at different voltages. This condition is maintained in a conductor by a cell or a battery.

Question 11.
In the circuit diagram shown, the two resistance wires A and B are of the same length and same material, but A is thicker than B. Which ammeter Af or A2 will indicate higher reading for current ? Give reason.
(CBSE 2010, 2011)

Answer:

The current will be high if resistence is low.

p and l for both wires A and B are same but area of cross-section (A) of wire A is- more than the wire B. Therefore, resistance of wire A is less than the resistance of the wire B. Hence, ammeter A connected in series with the wire A will indicate higher reading for current.

Question 12.
In the circuit diagram shown, the two resistance wires A and B are of same area of cross-section and same material, but A is longer than B. Which ammeter A₁ and A₂ will indicate higher reading of current ? Give reason. (CBSE 2010, 2011)

Answer:
The current in the circuit is high if the resistance of the circuit is low. Since wire A is longer than B, so the resistance of wire B is less than the resistance of wire A. Hence, current flowing through wire B is greater than the current flowing through wire A. Therefore, ammeter A₂ will indicate higher reading of current.

Question 13.
Two students perform experiments on two given resistors R₁ and R₂ and plot the following V-I graphs. If R₁ > R₂, which of the two diagrams correctly represent the situation on the plotted curves ? Justify your answer. (CBSE 2010, 2012)

Answer:
Resistance of a conductor = slope of I-V graph. It means, resistance is high if slope of I-V graph for it is steeper. Since R₁ > R₂, therefore, slope of I-V graph for R₁ must be steeper than the slope of I-V graph for R₂ Thus, diagram I represents the situation correctly.

Question 14.
Is the circuit given below correct ? Justify your answer. (CBSE 2014)

Answer:
The given circuit is incorrect because in a circuit, ammeter is always connected in series and voltmeter is connected parallel to the resistor R₁. The correct circuit is shown in figure.

Question 15.
List two distinguishing features between the resistance and resistivity of a conductor. (CBSE 2014)
Answer:

1. Resistance of a conductor depends on the length and area of cross-section of the conductor. On the other hand, resistivity of a conductor is independent of length and area of cross-section of the conductor.
2. Unit of resistance is ohm. Unit of resistivity is ohm-metre.

Based on resistors connected in series and parallel

Question 16.
Draw a schematic diagram of a circuit consisting of a battery of 12V, three resistors of 5Ω, 10Ω and 20Ω connected in parallel, an ammeter to measure the total current through the circuit, voltmeter to measue the potential difference across the combination of resistors. [CBSE (All India) 2008]
Answer:

Question 17.
(a) Why an ammeter likely to bum out if you connect it in parallel ?
(b) Why is series arrangement not found satisfactory for domestic lights ?(CBSE 2010, 2011)
Answer:
(a) Ammeter is a low resistance device. If it is connected in parallel, a large current flows through it. Hence, large heat is produced and it may burn the ammeter.
(b) If domestic lights are connected in series, then all lights will be switched off even when only one light fuses.

Question 18.
Draw diagrams to show series and parallel combinations of resistors. State three salient features each of both the combinations. (CBSE 2015)
Answer:


Salient features of series combination :

1. The net resistance of the combination is equal to the sum of the resistances of the individual resistor.
2. The current flowing through each resistor is the same.
3. The voltage applied across the series combination of resistors is equal to the sum of potential differences across the individual resistors.

Salient features of parallel combination :

1. The reciprocal of the net resistance of the combination is equal to the sum of the reciprocal of the resistances of the individual resistors.
2. Different amount of current flows through each resistor.
3. The potential difference across each resistor is equal to the voltage applied across the combination.

Based on heating effect of electric current

Question 19.
Why is the tungsten used almost exclusively for filament of electric lamps ?
                                                            Or
Why is Tungsten used for the filament in electric bulb ? (CBSE 2011, 2014, 2015)
Answer:
This is because

1. melting point of tungsten is very high (about 3380°C) and
2. it does not oxidise (or burn) even at higher temperatures.

Question 20.
Why do copper or aluminium wires usually used for electricity transmission and distribution purposes ?
(CBSE 2012, 2013)
                                                           Or
Copper and aluminium wires are usually employed for electricity transmission. Explain reason.
Answer:
The resistivities of copper and aluminium are very low, so electric current flows easily through them. Hence, copper and aluminium wires are usually used for electricity transmission and distribution purpose.

Question 21.
Should the heating element of an electric iron be made of iron, silver or nichrome wire 1
[CBSE (Foreign)2005, 2016]
                                                          Or
List two reasons why nichrome is used for making heating element of electrical appliances. (CBSE 2015)
Answer:
It should be made of nichrome wire because

1. resistivity of nichrome is greater than that of iron and silver,so more heat is produced in the nichrome wire due to the flow of current.
2. melting point of nichrome wire is greater than that of iron and silver and hence it does not melt easily on heating.
3. nichrome wire does not oxidise (or burn) easily even at higher temperature.

Question 22.
Two identical immersion heaters are to be used to heat water in a large container. Which one of the following
arrangement would heat the water faster,

1. connecting the heaters in series with the main supply,
2. connecting the heaters in parallel with the main supply ? (CBSE 2011)

Answer:
Heat produced in a heater, when connected to main supply,

When identical heaters (i.e. having same resistance) are connected in parallel, their net resistance decreases as compared to when connected in series. Therefore, heaters connected in parallel would heat the water faster as the heat produced in parallel combination is more than the heat produced in series combination, on electric energy and electric power

Question 23.
What is commercial unit of electrical energy ? Express it in joules. (CBSE 2015)
                                            Or
Define 1 kWh. How is this unit of energy related to 1 joule ? (CBSE 2011, 2015)
                                           Or
Establish the relationship between 1 kWh and SI unit of energy (joule). (CBSE 2012, 2013, 2015)
Answer:
Commercial unit of electrical energy is kWh. 1 kWh is the amount of electric energy consumed by 1000 W electric appliance when operates for 1 hour. 1 kWh = 1000 W x 3600 s = 1000 Js^-1 x 3600 s = 3.6 x 10⁶ J.

Question 24.
Two electric bulbs A and B are marked 220V, 40W and 220 V, 60W respectively. Which one of the two has greater resistance ? (CBSE 2010, 2011)
Answer:

Therefore, bulb A (40 W) has greater resistance than the bulb B (60 W)

Question 25.
Define electric power. A device of resistance R is connected across a source ofV voltage and draws a current I. Derive an expression for power in terms of voltage and resistance.
Answer:
Electric power is defined as the amount of electric work or electric energy per unit time.
If W be the amount of electric energy consumed in a circuit in t seconds, then the electric power is given by

Thus, electric power is defined as the product of potential difference applied across the circuit and current flowing through it.

Units of Power:

Long Answer Questions (5 Marks)

Question 1.
State Ohm’s law. How can this law be verified experimentally ? Does Ohm’s law hold good under all conditions.
Comment. (NCERT Question Bank, CBSE, 2010, 2012)
Answer:
For Ohm’s law: Ohm’s law states that the electric current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and . other physical conditions of the conductor remain the same.
For experimental verification: Verify Ohm’s law
Apparatus : A conductor of resistance R, an ammeter, a voltmeter, a battery, a variable resistance (or rheostat used to change the current in the circuit), connecting wires, a key and sand paper.
Procedure:

1. 1. Connect the various components as shown in figure 12.
      
   2. Close the key, so that current begins to flow in the circuit.
   3. Note down the potential difference (V) across the conductor PQ of resistance R shown by the voltmeter and the corresponding current (I) shown by the ammeter.
   4. Now move the knob of rheostat so that the current in the circuit increases.
   5. Again note down the potential difference (V) across the conductor PQ of resistance R in the voltmeter and current in the circuit shown by ammeter.
   6. Repeat the experiment at least five times by increasing the current in the circuit by moving the knob of the rheostat in steps.

Observations:

S.No	Potential Difference  (V)	Current (I)	V/I
1.
2.
3.
4.
5.
6.
7.

Plot a graph between V and I by taking V along X-axis and I along Y-axis. We get a straight line passing through origin as shown in figure 11.

Conclusion: From the graph between V and I, we conclude that I x V, which is Ohm’s law. Hence Ohm’s law is verified experimentally.
Precautions: While verifying Ohm’s law experimentally, the following precautions should be taken :

1. Current should not be allowed to pass through the circuit continuously for a long time, which may cause the increase in temperature of the conductor. Therefore, the plug of the key must be taken out every time after noting the readings of ammeter and voltmeter.
2. Connections should be tight.
3. The conductor used in the experiment should be such that its resistance is not changed with increase in temperature of the conductor.

Ohm’s law holds good if the temperature of the conductor remains the same.

Question 2.
How will you infer with the help of an experiment that same voltage or potential difference exists across three resistors connectred in parallel arrangement to a battery ?
Answer:
Perform an activity to investigate the relation between potential difference across parallel combination of resistors and the potential difference across each individual resistors,

1. Connect three resistors of resistances R₁, R₂ and R₃ in parallel. One end of each resistor is joined at a common point ‘a’ and the other end of each resistor is connected at another common point ‘b’.
2. Connect the parallel combination of resistors with a battery, a plug key K and an ammeter A as shown in figure 22(A).
   
3. Now connect a voltmeter across the parallel combination of resistors between a and b points.
4. Note the reading of voltmeter. Let it be V. This is the potential difference across the parallel combination of resistors.
5. Now, disconnect the voltmeter and connect it across R₁ as shown in figure 22(B).
   
6. Note the reading of voltmeter. It is found to be V.
7. Disconnect the voltmeter and connect it across R₂. Note the reading of voltmeter. It is found to be V.
8. Again disconnect the voltmeter and connect it across R₃. Note the reading of voltmeter. It is found to be V.

Conclusion : When resistors are connected in parallel to each other, potential difference across each resistor is equal to the potential difference across the parallel combination of resistors.

Question 3.
Describe an experiment to study the factors on which the resistance ofa conductor or a conducting wire depends.
Answer:
For experiment:
Connect the various electrical components as shown in figure 15.

1. Dependence of length of a conductor: 
   Take a copper wire of length l and connect it between the terminals A and B. Note the reading of ammeter. Now take another copper wire of same area of cross-section but of length 2l. Connect it between the terminals A and B by disconnecting the previous wire. Again, note the reading of ammeter. It will be found that the reading of ammeter (i.e., electric current) in the second case is half of the reading of ammeter in the first case. Since R = V/I, so resistance of second wire is double than the resistance of the first wire. Thus, resistance of a conductor is directly proportional to the length of the conductor,
   i.e      resistance ∝ length of the conductor
   Thus, more is the length of a conductor, more is its resistance.
   Thus, the resistance of’a conductor is ‘inversely proportional to the area of cross -section of the conductor.
2. Dependence on area of cross-section of a conductor:
   Now take two copper wires of same length but of different area of cross-sections. Let area of cross-section of first wire is more than the area of cross-section of the second wire. Connect first wire between the terminals A and B in the circuit shown in figure 15. Note the reading of ammeter. Now disconnect the first wire and connect the second wire between the terminals A and B. Again note the reading of the ammeter. It will be found that the reading of ammeter (i.e. electric current) is more when first wire (i.e. thick wire) is connected between A and B than the reading of the ammeter when second wire (i.e. thin wire) is connected between the terminals A and B.
   
   Thus, the resistance of a thin wire is more than the resistance of a thick wire.
3. Effect of the Nature of material:
   Take two identical wires, one of copper and other of aluminium. Connect the copper wire between the terminals A and B. Note the reading of ammeter. Now, connect the aluminium wire between the terminals A and B. Again note the reading of ammeter. It is found that the reading of ammeter when copper wire is connected in the circuit is more than the reading of the ammeter when aluminium wire is connected in the circuit.
   Therefore, resistance of copper wire is less than the resistance of aluminium wire. Hence, resistance of a wire or a conductor depends upon the nature of the material of the conductor.
4. Effect of temperature of conductor:
   If the temperature of a metallic conductor connected in the circuit increases, its resistance increases.
   Thus, factors on which resistance of a conductor depends are :
   1. its length,
   2. its area of cross-section,
   3. the nature of its material and
   4. its temperature.

The various factors affecting resistance of a conductor are given in table 1.
Table 1. Factors affecting resistance of a conductor:

Question 4.
What is Joule’s heating effect ? List applications of Joule’s heating effect in daily life.
(NCERT Question Bank, CBSE 2012, 2014, 2015)
Answer:
Joule’s law can be stated as : The amount of heat produced in a conductor is
(i) directly proportional to the square of the electric current flowing through it.
This is                  H ∝ I²                                                           –
(ii) directly proportional to the resistance of the conductor or resistor.
That is,                H ∝ R                                          ‘
(iii) directly proportional to the time for which the electric current flows through the conductor or resistor.
That is,               H ∝ t
Combining (i), (ii) and (iii), we get H ∝ I² Rt.
or         H = KI²Rt, where K is constant of proportionality
If          K = 1, then H = I²Rt joule
This is known as Joule’s law of heating.
Four Applications:

1. When electric appliances like electric heater, electric iron and water heater etc. are connected to the main supply of electricity, these appliances become hot but the connecting wires remain cold.
   We know, heat produced is directly proportional to the resistance of the material through which current flows. The element of electric heater is made of nichrome. Since, resistance of nichrome is high, so a large amount of heat is produced in the element of the electric heater. Thus, filament of electric heater becomes red hot. However, heat produced in connecting wires made of copper or aluminium is very small and hence they are not heated up.
   
2. Filament of an electric bulb is made of a thin wire of tungsten. The melting point of filament is high i.e., about 3380 °C. The filament of the bulb is enclosed in a glass envelope fixed over an insulated support as shown in figure 28. The glass envelope of electric bulb is filled with inactive gases like nitrogen and argon to increase the life of the tungsten filament.
   Since resistance of thin filament is very high, so a large heat is produced as the electric current flows through the filament. Due to this large amount of heat produced, filament of the bulb becomes white hot. Hence, the filament of the bulb emits light and heat.
   
3. Electric fuse is a safety device connected in series with the electric circuit. Electric fuse is a wire made of a material whose melting point is very low. Examples of the materials of making fuse wire are copper or tin-lead alloy. When large current flows through a circuit and hence through a fuse wire, a large amount of heat is produced. Due to this large amount of heat, the fuse wire melts and the circuit is broken so that current stops flowing in the circuit. This saves the electric circuit from burning due to the passage of large current through it.
   

 

Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 12 Electricity are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 15 Our Environment Class 10 Science Important Questions with Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Our Environment Class 10 Important Questions and Answers Science Chapter 15

Very Short Answer Questions (1 Mark Each)

Question 1.
What is environment ? (CBSE Foreign 2006, 2016, CCE 2012)
Answer:
It is sum total of all external factors, substances, conditions and living beings that surround the organisms and influence the same without becoming their part.

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
Why is ozone layer getting depleted at higher levels of the atmosphere ?  (CBSE Delhi 2008 C, CCE 2011)
Answer:
Presence of ozone depleting chemicals like chlorofluorocarbons.

Question 3.
Name any two abiotic components of an environment. (CBSE Delhi 2008 C)
Answer:
(a) Climatic factors (light, temperature, rainfall).
(b) Edaphic factors (soil and its conditions).

Question 4.
What are two main components of our environment ? (CBSE Delhi 2009, CCE 2012)
Answer:
(a) Biotic Components, e.g., producers, herbivores, carnivores, decomposers.
(b) Abiotic Components e.g., climatic factors, edaphic factors, topographic factors, inorganic nutrients and organic substances.

Question 5.
Which compounds are responsible for the depletion of ozone layer ? (CBSE A.I. 2009)
Answer:
Ozone depleting substances like chlorofluorocarbons, halons, methane, N2O, Chlorine, Carbon tetrachloride.

Question 6.
Why are green plants called producers ? (CBSE A.I. 2009, Delhi 2016, CCE 2011)
Answer:
Green plants are also called producers because only they can synthesise organic food from inorganic raw materials with the help of solar energy in the process of photosynthesis. This food is not only used by green plants but also all other organisms called consumers.

Question 7.
The flow of energy in the food chain is unidirectional. Why ? (CCE 2011 )
Answer:
There is dissipation of energy at every step of its transfer and transformation so that energy cannot flow back
in the reverse direction. It flows from sun to plants, plants to animals, animals to animls, organic remains to decomposers and dissipation as heat at every stage.

Question 8.
Use of paper is more environment friendly than the use of polythene for packaging. Justify. (CCE 2011)
Answer:
Paper bags are biodegradable while polythene is nonbiodegradable.

Question 9.
In a food chain comprising frogs, insects, birds and grass, which one of the organisms is likely to have maximum concentration of harmful non-biodegradable chemicals in the body. (CCE 2011)
Answer:
Birds, as they form the topmost trophic level where the non-biodegradable chemicals will have maximum biomagnification.

Question 10.
State one advantage of using disposable paper cups over disposable plastic cups. (CCE 2011)
Answer:
Disposable paper cups are biodegradable while disposable plastic cups are non-biodegradable.

Question 11.
Give an example of food chain of four trophic levels that exists in a grassland. (CCE 2011)
Answer:

Question 12.
Write the full form of CFC. (CCE 2011)
Answer:
Chlorofluorocarbon.

Question 13.
In a certain study conducted on the occurrence of DDT along food chains in an ecosystem, the concentration of DDT in grass was found to be 0-5 ppm. In sheep, it was 2 ppm and in man it was 10 ppm. Why was the concentration of DDT maximum in case of man ? (CCE 2011)
Answer:
DDT is a non-biodegradable chemical which not only accumulates in each trophic level but also undergoes biomagnification with the rise in trophic level. DDT concentration is maximum in man as man is occupying the highest trophic level.

Question 14.
Why there has been a large hue and cry against the use of CFCs ? (CCE 2011, CBSE Foreign 2016)
Answer:
CFCs (Chlorofluorocarbons) pass on to the upper layers of atmosphere, i.e., stratosphere, where ozone layer is based. CFCs cause depletion of ozone layer that allows harmful UV radiations to reach the surface of the earth causing skin cancers and defective eye sight.

Question 15.
Select the biodegradable wastes : DDT, crop residue, leather, glass. (CCE 2011)
Answer:
Crop residue, leather.

Question 16.
In a food chain consisting of snake, insect, grass and frog, assign an appropriate trophic level to frog.
(CCE 2011, CBSEA.I. 2016)
Answer:

Question 17.
What are the three ‘Rs’ in saving the environment ? (CCE 2011)
Answer:
Reduce, recycle and reuse.

Question 18.
In the following food chain, 5 J of energy is available to man. How much energy was available at the producer level ?(CCE 2011)

Answer:
Man 5 J, sheep 5 x 10 = 50 J, plants 50 x 10 = 500 J.

Question 19.
Name the disease caused in human beings due to depletion of ozone layer in the atmosphere. (CCE 2011)
Answer:
Skin cancer.

Question 20.
Name any two non-biodegradable wastes. (CCE 2011)
Answer:
Waste plastic articles, polythene bags, many pesticides like DDT.

Question 21.
Define the term biomagnification. (CCE 2011)
Answer:
Biomagnification is the increase in the level of a non-biodegradable substance with each successive rise in the trophic level of a food chain.

Question 22.
What is depicted in the scheme ? (CCE 2011)

Answer:
It is a food chain that is depicting 10% law of energy.

Question 23.
Ozone is deadly poisonous. Still it performs an essential function. How ? (CCE 2011)
Answer:
Ozone present in the ozone layer of the stratosphere dissipates and hence filters out high energy UV radiations (100 —320 nm) of the sun and protects the earth from the same.

Question 24.
Which of the following belong to the first trophic level : Grasshopper, Rose plant, Neem plant, Cockcroach, Vulture. (CCE 2011)
Answer:
Rose plant, Neem plant.

Question 25.
What would happen to the environment if decomposers were not present ? (CCE 2011)
Answer:
Organic remains will pile up and all the biogenetic nutrients will get tied up in organic matter with no further scope of manufacture of more organic matter.

Question 26.
Which one of the following organisms comprising a food chain will possibly have the maximum concentration of harmful chemicals in its body :
Peacock, Frog, Grass, Snake, Grasshopper. (CCE 2011)
Answer:
Peacock as it lies at the top of food chain :
Grass ———> Grasshopper ———> Frog ———> Snake ———> Peacock.

Question 27.
Phytoplankton ———> Zooplankton ———> Fish ———> Fish eating Bird.
In this food chain which organisms will have

1. Maximum available energy
2. Maximum concentration of pesticides. (CCE 2011)

Answer:

1. Phytoplankton
2. Fish eating birds.

Question 28.
List two man-made ecosystems. (CCE 2011, CBSE Foreign 2017)
Answer:
Cropland, aquarium.

Question 29.
Which of the following materials are biodegradable : Glass, leather, glucose, silver foil ? (CCE 2011)
Answer:
Leather, glucose.

Question 30.
Mention any two methods of garbage disposal. (CCE 2011)
Answer:
Composting, manure and biogas.

Question 31.
Why is depletion of ozone layer a cause of concern ? (CCE 2011, CBSEA.I. 2016)
Answer:
Depletion of ozone layer is causing increased number of skin cancers, cataracts and reduced immunity in human beings.

Question 32.
How can we help in reducing the problem of waste disposal ? List any two ways. (CCE 2011)
Answer:

1. Separation of biodegradable and non-biodegradable wastes,
2. Preparation of compost or vermicompost from biodegradable waste and handing over the recyclable non-biodegradable wastes to rag pickers.

Question 33.
Which one of the following food habits is better and why :
(a) Plant ———> Man
(b) Plant ———> Goat ———> Man. (CCE 2011)
Answer:
Plant ———> Man as it makes more energy available (ten percent law).

Question 34.
Name the type of compounds which are used as refrigerants and in fire extinguishers that deplete the ozone layer in the atmosphere. (CCE 2011)
Answer:
Chlorofluorocarbons (as refrigerants) and halons (in fire extinguishers).

Question 35.
Producers always occupy the first trophic level in any food chain. Why ? (CCE2011, C.B S.E. Foreign 2016)
Answer:
Only producers have the ability to trap solar energy and manufacture organic food through the process of photosynthesis.

Question 36.
A list of organisms is given below : Peacock, Snake, Gross, Frog, Grasshopper. Construct a food chain showing snake at the fourth place. (CCE 2011)
Answer:

Question 37.
“Save the tiger” campaign is being over-emphasized these days by our Government. What may be the possible reason ? (CCE 2011)
Answer:
To maintain the ecological balance which is effected through biocontrols.

Question 38.
Why are plastics non-biodegradable substances ? (CCE 2011)
Answer:
Plastics are non-biodegradable substances as they cannot be broken down by decomposers. Their wastes pile up‘ . . . .

Question 39.
What step is being taken to limit the damage to ozone layer ? (CCE 2011)
Answer:
Stopping manufacture of chlorofluorocarbons and halons and replacing them with ozone friendly substances.

Question 40.
Which gas shields the surface of earth from harmful radiations of the sun ? Why are UV radiations harmful to organisms ? (CCE 2012)
Answer:
Ozone.
Harmful Effects of UV Radiation.

1. Skin cancer, cataract and fall of immunity in humans.
2. More mutations, fall in photosynthesis, blinding of animals, killing of their young ones.

Question 41.
List two raw materials used by living organisms of the first trophic level for making food. (CCE 2012)
Answer:
CO₂, H₂O and minerals. Energy is obtained from sun.

Question 42.
Which of the following are biodegradable : Gold coin, glass, nylon cloth, oil, silver foil, leather. (CCE 2012)
Answer:
Oil. leather.

Question 43.
In the food chain comprising Tiger, Plants and Goats, which will
(a) Transfer the maximum amount of energy
(b) Receive minimum amount of energy ? (CCE 2012)
Answer:
(a) Transfer of Maximum Energy. Plants
(b) Receive Minimum Energy. Lion.

Question 44.
Identify producers from the following : Frog, Blue-green algae, Grass hopper, Fish, Grass. (CCE 2012)
Answer:
Blue-green algae, Grass.

Question 45.
Draw a line diagram to show flow of solar energy in ecosystem. (CCE 2012)
Answer:

Question 46.
What is 10% law in the context of energy transfer in food chains ? (CCE 2012)
Answer:
10% Law (Lindeman, 1942). Energy available decreases by 90% with the rise in trophic level so that higher trophic level comes to have only 10% of energy present in lower trophic level.

Question 47.
Why do man-made materials like plastics persist for a long time in our environment ? (CCE 2012)
Answer:
Man made materials like plastics are non-biodegradable because decomposers do not have enzymes to degrade them.

Question 48.
A geographical area contains organisms like snake, grass hopper, peacock, grass and frog. If pesticides was used in this area to kill insects which among the organisms will have maximum amount of pesticide. Name the phenomenon involved. (CCE 2012)
Answer:
Peacock will have maximum concentration of pesticide as it lies at the top of food chain. The phenomenon involved in increase in pesticide concentration at higher trophic level is called biomagnification.

Question 49.
Name any two non-biodegradable wastes generated daily in household activities. (CCE 2012)
Answer:
Milk pouches, polythene bags.

Question 50.
State a way to prevent accumulation of harmful chemicals in our bodies. (CCE 2012)
Answer:

1. Use of organic foods.
2. RO treated drinking water.
3. Minimum use of pesticides at home. Instead, stress should be on cleanliness and double doors.

Question 51.
Write the appropriate names of trophic levels Z and X in the figure. (CCE 2012)
Answer:
X: Primary consumer.
Z: Tertiary consumer.

Question 52.
Which chemical is used as fire extinguishers ? How is it harmful ? (CCE 2012)
Answer:
Halon or bromine containing gas, e.g., bromochlorodifluoromethane.
It causes depletion of ozone in the stratosphere.

Question 53.
Pick up non-biodegradable substance from the following : Animal bones, wool, paper, glass. (CCE 2012)
Answer:
Glass.

Question 54.
What is ecosystem ? (CCE 2012, CBSE Delhi 2017)
Answer:
Ecosystem is self sustained ecological system which consists of a distinct biotic community and the physical environment both interacting and exchanging materials between them.

Question 55.
Select the biotic components of the environment from the following : Fungi, Soil, Mango Tree, Temperature. (CCE 2012)
Answer:
Fungi, Mango tree.

Question 56.
Why is the Government stressing upon the use of jute/cloth carry bags ? (CCE 2012)
Answer:

1. Cloth bags are stronger and more durable as compared to plastic bags.
2. They are washable.
3. They are reused time and again.
4. Cloth bags do not pollute environment.
5. They are made of biodegradable material which can also be recycled.

Question 57.
Why should biodegradable and nonbiodegradable wastes be discarded in two separate dust bins ? (CCE 2013)
Answer:
So that the two can be easily disposed off without causing much littering and stink

1. Disposable directly to composting and gasification plants,
2. Nondisposable for separation into recyclable and nonrecyclable (landfill) components.

Question 58.
What will be the amount of energy available to the organisms of the second trophic level of food chain, if the energy available at the first trophic level in 10,000 Joules ? (CCE 2015)
Answer:
1000 Joules (10% Law).

Question 59.
Which of the following are always at the second trophic level of food, chains : Carnivores, Autotrophs, Herbivores ? (CCE 2015)
Answer:
Herbivores.

Question 60.
From the following list find out the organism which is likely to have maximum concentration of pesticide in the body-Grass, grasshopper, frog, snake and hawk. (CCE 2015)
Answer:
Hawk, because it lies at the top of food chain where maximum bio-magnification of pesticide concentration will occur.

Question 61.
Suggest a food chain in which one of the trophic level is occupied by humans. (CCE 2015)
Answer:
Wheat ———> Human; Grass ———> Goat ———> Human.

Question 62.
Differentiate between the food habits of organisms belonging to first and second trophic levels.
Answer:
Organisms of first trophic are producers. Organisms of second trophic level are herbivores. Producers are autotrophic, i.e., manufacture their own food from inorganic raw materials. Herbivores are animals which feed on producers for obtaining food and its contained energy.

Question 63.
List two natural ecosystems. (CBSE Delhi 2016, Foreign 2017)
Answer:
Forest, lake/pond.

Question 64.
List two biotic components of biosphere. (CBSE Delhi 2016)
Answer:
Plants, animals, microorganisms

Question 65.
Why is forest/lake considered a natural ecosystem ? (CBSE Delhi 2017)
Answer:
It is a self sustained ecological system.

Question 66.
In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer ? (CBSE A.I. 2017)
Answer:
Plants ———> Deer ———> Lion.
Energy available to deer = 100J x 10 = 1000 J
Energy available to plants = 1000 x 10 = 10,000 J.

Question 67.
In the following food chain, plants provide 500J of energy to rats. How much of energy will be available to hawks from snakes ?
Plants ———> Rats ———> Snakes ———> Hawks (CBSE A.I. 2017)
Answer:
Energy available to snakes from rats
500 J % 10 = 50 J
Energy available to hawks = 50 J% 10 = 5J.

Question 68.
In the following food chain, 20000J of energy was available to the plants. How much energy would be available to man in this chain ?
Plant ———> Sheep ———> Man (CBSE A.I. 2017)
Answer:
Out of the energy available to plants, the amount of energy trapped by them and available to sheep is 1%. 20000 x 100% = 200J
Energy available to sheep = 200 10 = 20 J
Energy available to man = 20 x 10% = 2 J.

Question 69.
List any two abiotic components of an ecosystem.
Answer:
Water, minerals, sunlight.

Short Answer Questions (2 Marks)

Question 1.
Construct an aquatic chain showing four trophic levels.
Answer:
Phytoplankton ———> Zooplankton ———> Small Carnivorous Fish –

Question 2.
Explain “biological magnification” with the help of an example.
Answer:
Biological magnification is increase in the concentration of a chemical per unit weight of the organisms with the successive rise in trophic level. In one study it was found that concentration of harmful chemical like DDT will increase 80,000 times the concentration present in water.

Question 3.
A high concentration of harmful chemical is highly injurious, even fatal, to higher trophic level organisms. Mention the basis of classifying substances as biodegradable and non-biodegradable. Give two examples of each. (CBSE Foreing 2010)
Answer:
Substances are classified into biodegradable and non-biodegradable on the basis of their disposability or nondisposability by saprophytic organisms.
Biodegradable. Used tea leaves, waste paper.
Non-biodegradable. DDT, silver/aluminium foil.

Question 4.
What is ozone ? How does it protect the organisms on the earth ? (CCE 2011)
Answer:
Ozone is triatomic form of oxygen, O₃. It forms a protective ozone layer in the stratosphere. Ozone layer absorbs the very harmful component of ultraviolet radiations (100 – 320 nm) and thus protect the organisms on the earth.

Question 5.
Observe the food chain :
Plant (1000 kj) ———> Goat ———> Lion
(a) If autotrophs occupying the first trophic level are called producers, what are herbivores called as ?
(b) How much energy does the lion get in the above food chain ? (CCE 2011)
Answer:
(a) Primary consumers
(b) 10 kj (10% law, 1000 ———> 100 ———> 10).

Question 6.
“The maximum concentration of harmful chemicals accumulates in human beings ?” State the phenomenon involved and justify this statement. (CCE 2011)
Answer:
Human beings are omnivorous and lie at the tip of almost every food chain. They are also long lived. Harmful chemicals reach in higher concentration through biomagnification and continue to accumulate in their bodies. Therefore, non-biodegradable chemicals occur in maximum concentration in human beings.

Question 7.
In the food chain Grass ———>Deer ———> Lion operating in a forest, what will happen if all the
(a) Lions are removed
(b) Deer are removed. (CCE 2011)
Answer:
(a) Removal of Lions. It will cause spurt in population of deer so much so that whole of grass can disappear resulting in conversion of the area into desert and death of the deer as well.
(b) Removal of Deer Lions will die of starvation.

Question 8.
Define
(a) Biomass
(b) Anaerobic degradation. (CCE 2011)
Answer:
(a) Biomass. It is the amount of living matter, measured as fresh or dry weight.
(b) Anaerobic Degradation. There is slowing down of rate of decomposition of organic remains which will pile up. Offensive odours may occur due to putrefaction of proteins while fermentation of carbohydrates gives rise to alcohols and organic acids that may kill the microbes. It is, however, useful in production of biogas.

Question 9.
We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest ways to make people realize that the improper disposal of waste is harmful to the environment. (CCE 2013)
Answer:
Domestic waste is often thrown outside the living quarters or some common place near the homes for municipal staff to pick up and dispose the same. The waste is, however, spread by stray cattle, pigs and dogs and is left to decompose. It is an improper method of waste disposal being harmful to environment as well as to all of us. It produces stink and becomes a source of several diseases. The scattered decomposing waste attracts flies, mosquitoes and rats.
Therefore, a proper waste disposal method involving biodegradable in covered green bins and nonbiodegradable in covered blue bins be adopted. The municipal staff can take the wastes from the bins.

Question 10.
Explain how ozone is formed in the atmosphere ? How does it protect living beings from harmful radiations of the sun ? (CCE 2013)
Answer:

1. Ozone is formed in the upper atmosphere by the action of ultraviolet (UV) radiations over oxygen (O₂)
   
2. Ozone present in the upper atmosphere protects us from extremely harmful high energy ultraviolet radiations (100-320 nm) by dissipating their energy.
   

Question 11.
Why is Government of India imposing a ban on the use of polythene bags ? Suggest two alternates to these bags and explain how this ban is likely to improve the environment. (CCE 2014)
Answer:
Polythene is nonbiodegradable. Use of polythene bags often chokes drains and kills animals feeding on garbage besides piling up in garbage disposal sites.
Alternates: Use of cloth bags and paper bags.
Environment: Cloth bags can be used and reused. Both cloth and paper bags are biodegradable.

Question 12.
List two reasons to show that the existence of decomposers is essential in an ecosystem. (CCE 2014)
Answer:

1. They function as saprophytes and cleanse the earth of organic remains.
2. Decomposers release minerals tied up in organic remains. They thus help in recycling of biogeochemicals. Recycling of paper, metal, plastic and e-waste is done at most of the places.

Question 13.
Mention the positive impact of this recycling process on environment. (CCE 2015)
Answer:

1. There will be reduced use of resources.
2. There will be little pollution from these wastes as they are picked up for recycling as soon they are produced.

Question 14.
It is said that there is need to put a complete ban on the products containing aerosols. What are aerosols ?
Why is there a demand to put a ban on them ? (CCE 2015)
Answer:
Aerosols are mist producing propellants used in sprays like deodrants, perfumes, after shaves, etc. They are commonly made of chlorofluorocarbons which are strongest ozone depleting substances. Therefore, there is a demand for putting a ban on them.

Question 15.
Food web is shown as a series of branching lines of food chains. Explain and justify the statement.
(CCE 20I5)
Answer:
Food web is a network of food chains occurring in an ecosystem which get connected at different trophic levels so as to form feeding connections or alternatives amongst different organisms of the community.
Because the food chain are connected at different trophic levels, connectives appear as branching lines of food chains.

Question 16.
Rohan was watching television when his mother instructed him to empty the home garbage bin which had become full, into public garbage bin. Rohan emptied the home garbage bin in front of his house as the public garbage bin was little far off. His mother saw him doing so. She tried to explain him the problems associated with improper garbage disposal.
(a) Mention any 2 problems, society faces due to improper garbage disposal.
(b) Mention two values displayed by Rohan’s mother. (CCE 2015)
Answer:
(a)

1. The garbage will be scattered by cattle and dogs, resulting in unhygienic condition.
2. Stink or foul smell will be produced by the decaying garbage due to emission of foul gases.
3. The decaying garbage becomes breeding place of flies and other pests which spread a number of diseases.

(b) Values :

1. Care for sanitary conditions all around.
2. Social consciousness
3. Teaching good habits.

Question 17.
Recycling is considered as a welcome practice to deal with the environmental problems. Justify the statement with two arguments ? (CCE 2015)
Answer:
Recycling is treatment of waste material so as to make it suitable for reuse, e.g., metallic articles, broken glass, paper, etc.

1. There will be reduced use of resources.
2. There will be little pollution from these wastes as they are picked up for recycling as soon they are produced.

Question 18.
We as an individual can contribue by becoming environmental friendly. What practices we can adopt in order to do so. (CBSE 2015)
Answer:

1. Use of cloth bags instead of polythene or plastic bags.
2. Separation of biodegradable and non-biodegradable in green and blue coloured bins.
3. Use of compact fluorescent lamps instead of incandescent lamps.
4. Harvesting of rain water and preventing wastage of resources.

Short Answer Questions (3 Marks Each)

Question 1.
Why are some substances biodegradable and some non-biodegradable ? (CBSE A.L 2007)
Answer:
Substances which can be degraded and disposed off naturally by saprophytic organisms or decomposers are called biodegradable, e.g, organic remains, garbage, sewage, livestock waste. Substances which cannot be degraded by saprophytes are known as non-biodegradable. They are mostly man-made articles like pesticides, plastic, polythene, synthetic fibres, etc. Biodegradable articles are formed naturally in biosphere. Decomposer organisms feed on them by secreting digestive juices and absorbing the solubilised substances. Biogenetic nutrients are released in the process called mineralisation. Non-biodegradable articles pile up in nature because decomposers do not have enzymes to degrade them.

Question 2.
“Damage to the ozone layer is a cause of concern.” Justify the statement. Suggest any two steps to limit this damage. (CBSE Delhi 2008 C)
Answer:
Cause of Concern: Ozone layer present in the stratosphere has thinned out by about 8% over the equator and more so over the antarctica where a big ozone hole appears every year. This has increased the level of UV-B radiations reaching the earth by 15-20%. These radiations are causing increased number of skin cancers, cataracts and reduced immunity in human beings. There is increased incidence of blinding of animals, death of young ones, reduced photosynthesis, higher number of mutations and damage to articles.
Steps to Limit Damage,

1. Ban on production and use of halons.
2. Ban on production and use of chlorofluorocarbons.

Question 3.
Distinguish between biodegradable and non-biodegradable substances. List two effects of each of them in our environment. (CBSE Delhi 2008 C)
Answer:
(a) Differences between Biodegradable and Non-biodegradable Substances:

Biodegradable Wastes	Non-biodegradable Wastes
1. Origin. They are biological in origin.	They are commonly man-made.
2. Degradability. The wastes are degraded by microorganisms.	They are not degraded by microorganisms.
3. Accumulation. They do not accumulate in nature.	They pile up and accumulate in nature.
4. Biomagnification. The biodegradable wastes do not show biomagnification.	The soluble non-degradable wastes enter food chains and undergo biomagnification.
5. Resource. The wastes can be converted into resource.	Some wastes can be recycled.
Examples. Garbage, livestock wastes, sewage.	Examples. Plastic, polythene, glass, nickel, cadmium, several pesticides.

(b) Effects of Biodegradable Substances:

1. Stink: Within a day or so waste biodegradable substances begin to stink and produce foul gases.
2. Pests and Pathogens: The decaying biodegradable substances become breeding places of flies and many other pests. They also contain a number of pathogens. Flies and other pests carry the germs to all the places visited by them resulting in spread of diseases.

(c) Effects of Non-biodegradable Substances:

1. Dumping Area: Dumping of non-biodegradable substances on a piece of land converts the same into barren land. It is also called landscape pollution.
2. Biological Magnification: Pesticides, heavy metals and other chemicals enter water and food chains. They accumulate in toxic proportions and harm all kinds of living organisms. Their concentration also increases with rise in trophic level. Human beings are harmed the most because man lies at the top of every food chain.

Question 4.
Why are bacteria and fungi called decomposers ? List any two advantages of decomposers to the environment.
(CCE 2011)
Answer:
Answer:
(a) Decomposers: Most of the bacteria and fungi are saprophytes. They obtain their nourishment from organic remains. For this they secrete digestive enzymes over the remains. The remains are converted into soluble absorbable form. This results in decomposition of organic matter. Therefore, bacteria and fungi are called decomposers.
(b) Advantages:

1. Scavengers: Decomposers function as scavengers by removing organic remains and cleansing the earth.
2. Mineralisation: Decomposers release inorganic nutrients trapped in organic remains. The same are recycled.

Question 5.
How is ozone formed in the upper atmosphere ? Why is damage to ozone layer cause of concern to us.
What causes this damage ? (CBSE A.I. 2008, 2008 C, Delhi 2009 C)
Answer:
(a) Formation of Ozone in Upper Atmosphere. High energy UV radiations split oxygen molecules into oxygen atoms. The latter react with oxygen molecules to form ozone (Molina and Molina, 1992)

(b) Damage to Ozone Layer Cause of Concern:
Ozone layer present in the stratosphere has thinned out by about 8% over the equator and more so over the antarctica where a big ozone hole appears every year. This has increased the level of UV-B radiations reaching the earth by 15-20%. These radiations are causing increased number of skin cancers, cataracts and reduced immunity in human beings. There is increased incidence of blinding of animals, death of young ones, reduced photosynthesis, higher number of mutations and damage to articles
(c) Causes of Damage. Presence of ozone depleting substances or ODS in the stratosphere ———> Halons,
chlorofluorocarbons, N₂O, Methane, Chlorine, Carbon tetrachloride.

Question 6.
State in brief two ways in which nonbiodegradable substances would affect the environment. List two methods of safe disposal of the nonbiodegradable waste. (CCE 2013)
Answer:
Effects on Environment:

1. Dumping Area: Dumping of non-biodegradable substances on a piece of land converts the same into barren land. It is also called landscape pollution.
2. Biological Magnification: Pesticides, heavy metals and other chemicals enter water and food chains. They accumulate in toxic proportions and harm all kinds of living organisms. Their concentration also increases with rise in trophic level. Human beings are harmed the most because man lies at the top of every food chain.

Safe Disposal:

1. Recycling: Metal, plastic and glass articles can be sent for recycling,
2. Sanitary Landfills: The nonrecyclable articles are dumped in specially prepared low lying area, compacted and covered by a layer of earth, lime and bleaching powder.

Question 7.
(a) What is an ecosystem ? List its two main components.
(b) We do not clean ponds or lakes but an aquarium needs to be cleaned regularly. Explain. (CCE 2013)
Answer:
(a) Ecosystem: It is self contained ecological system, which consists of a distinct, biotic community and the physical environment both interacting and exchanging materials between them.
Main Components,

1. Biotic, e.g., producers, consumers
2. Abiotic, e.g., climatic factors, inorganic nutrients.

(b) Cleaning an aquarium:
An aquarium is an artificial system which is also incomplete due to absence of producers, food chains and decomposers. There is no recycling and self cleaning. However, a pond or a lake is a self sustained, natural and complete ecosystem where there is perfect recycling of nutrients.

Question 8.
“Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues”. State the reason to explain how and why it happens ? (CCE 2014)
Answer:
Crops are often sprayed with pesticides in order to prevent loss due to attack of pests. The sprayed pesticides enter the food crops, soil, vegetation and water. As a result grains like wheat and rice, vegetables, fruits and meat of animals come to have varying amounts of pesticides.

Question 9.
“Energy flow in a food chain is unidirectional”. Justify this statement. Explain how the pesticides enter food chain and subsequently get into our body. (CCE 2014)
Answer:
Energy Flow is Unidirectional:
An ecosystem does not have its own source of energy. It receives the same from sun. Green plants or producers trap the solar energy and change it into chemical form during synthesis of food. Herbivores obtain energy from the food they take. A lot of energy dissipates during transfer and utilization of food energy by herbivores (10% law). From herbivores the food energy passes to primary carnivores. However, only about 10% of herbivore energy is passed into body mass of primary carnivores.
The rest is dissipated. From primary carnivores the energy passes into secondary carnivores (10%), etc. It is ultimately lost as heat.

Since energy available decreases at every tophic level, very little of it is available at higher trophic levels. There is dissipation of energy at every step of its transfer and transformation. Hence it cannot flow in the reverse direction i.e., energy flow is unidirectional from sun to plants, plants to animals, animals to animals, organic remains to decomposers and dissipation as heat.
Pesticides: Pesticides are sprayed over crop plants in order to protect them from pests. They not only enter the crop plants but also pass into soil and reach water table as well as water bodies where they become part of food chain. With rise of trophic level the/ undergo biomagnification. Human beings obtain the pesticides from their food. They accumulate in human body in toxic amounts as human beings are long lived and continue to feed on pesticide contaminated foods.

Question 10.
Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose non-biodegradable waste, for saving the environment. (CCE 2015)
Answer:
Differences :

Biodegradable Wastes	Non-biodegradable Wastes
1. Origin. They are biological in origin.	They are commonly man-made.
2. Degradability. The wastes are degraded by microorganisms.	They are not degraded by microorganisms.
3. Accumulation. They do not accumulate in nature.	They pile up and accumulate in nature.
4. Biomagnification. The biodegradable wastes do not show biomagnification.	The soluble non-degradable wastes enter food chains and undergo biomagnification.
5. Resource. The wastes can be converted into resource.	Some wastes can be recycled.
Examples. Garbage, livestock wastes, sewage.	Examples. Plastic, polythene, glass, nickel, cadmium, several pesticides.

Change in Habits :

1. Reduce, reuse and recycle of non-biodegradable wastes can save the environment.
2. Non-biodegradable materials which cannot be recycled are employed in sanitary land fills.
3. Segregation of non-biodegradable wastes and putting them into separate dustbin (blue) for disposal.
4. Use of cotton and jute bags for shopping, vegetables, fruits and other articles.

Question 11.
If all the wastes we generate are biodegradable, what effect will this have on the environment ? Write two values which will be imbibed if people are made to understand that generation of waste should be restricted to be biodegradable only. (CCE 2015)
Answer:
There will be no piling up of wastes nor any problem of their disposal. Bio-degradable wastes are natural and can be made to decompose naturally. Rather, it can produce useful materials like biogas and manure.
Values:

1. No third pollution,
2. Disappearance of many diseases.
3. Greener earth and cleaner water.

Question 12.
After the examination, Rakesh with his friends went on a picnic to nearby park. All freinds carried cooked food packed in plastic bags or plastic cans. After eating the food, some freinds collected.the left over food and plastic bags, etc. and planned to dispose them off by burning. Rakesh inmediately checked them and suggested to segregated left over food and peels of fruits from plastic materials and respectively dispose them off separately in green and red dustbins placed into corner of the park.
(a) In your opinion, is burning plastic an eco-freindly method of waste disposal ? Why ? State the advantage of method suggested by Rakesh.
(b) How can we contribute in maintaining the parks and roads, neat and clean ? (CCE 2015)
Answer:
(a) No. Burning of plastic releases a number of toxic chemicals which are harmful to humans, animals and plants besides polluting the environment. Segregating the wastes and placing them in different bins (green for biodegradable and red for non-biodegradable wastes) is an eco-freindly disposal.
(b) Parks and roads can be kept neat and clean by keeping dust bins at selected places and asking the users to throw the wastes only in the bins meant for them.

Question 13.
Sita and Lata are neighbours in a colony. Sita maintains a compost pit by using bio-degradable household wastes. Lata throws the household waste in two separate dustbins.
(a) Whom do you support ? Why ?
(b) How is Sita justified.
(c) Maintaining two dustbins for bio-degradable and non-biodegradable wastes is a good idea.
How is Sita’s practice better than that of Lata ? (CCE 2015)
Answer:
(a) Sita. She is sparing the municipal committee of picking up biodegradable waste and transporting the same to disposable sites.
(b) Sita is producing her own compost for her home garden. She is not only saving money on purchase of manure and fertilizer but is also practising organic farming.
(c) Lata’s practice of keeping two separate bins of bio-degradable and non-biodegradable garbage is most suitable but Sita’s practice is better as it reduces the bulk of garbage and saves on money.

Question 14.
Give reason to justify the following :
(a) The existence of decomposers is essential in the biosphere.
(b) Flow of energy in a food chain is unidirectional. (CBSE Delhi 2016)
Answer:
(a)

1. They function as saprophytes and cleanse the earth of organic remains.
2. Decomposers release minerals tied up in organic remains. They thus help in recycling of biogeochemicals. Recycling of paper, metal, plastic and e-waste is done at most of the places.

(b) An ecosystem does not have its own source of energy. It receives the same from sun. Green plants or producers trap the solar energy and change it into chemical form during synthesis of food. Herbivores obtain energy from the food they take. A lot of energy dissipates during transfer and utilization of food energy by herbivores (10% law). From herbivores the food energy passes to primary carnivores. However, only about 10% of herbivore energy is passed into body mass of primary carnivores.
The rest is dissipated. From primary carnivores the energy passes into secondary carnivores (10%), etc. It is ultimately lost as heat.

Since energy available decreases at every tophic level, very little of it is available at higher trophic levels. There is dissipation of energy at every step of its transfer and transformation. Hence it cannot flow in the reverse direction i.e., energy flow is unidirectional from sun to plants, plants to animals, animals to animals, organic remains to decomposers and dissipation as heat.

Question 15.
Your mother always thought that fruit juices are very healthy for everyone. One day she read in the newspaper that some brands of fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to our health.
(a) How would you explain to your mother about fruit juices getting contaminated with pesticides.
(b) It is said that when harmful pesticides enter our body as well as in the bodies of other organisms, they get accumulated and beyond a limit cause harm and damage to our organs. Name the phenomenon and write about it. (CBSE A.I. 2017)
Answer:
(a) During growth of plants and formation of fruits, the plants are often sprayed with pesticides to protect them from pests and pathogens.

1. A small quantity of pesticides does enter the fruits and other parts of crop plants,
2. A good quantity of pesticides seep into soil and reach the ground water. The pesticide contaminated ground water also enters the crop plants. It also causes contamination of fruit juices if such a water is used during preparation of juices.

(b) From fruit juices, other plant products and ground water the pesticides enter our bodies as well as bodies of other organisms which pass the same to humans through food chain. Beyond a certain level, the pesticides become toxic, harming our vital organs.
Definition. The increase in concentration of non-biodegradable substances in the bodies of organisms with time and rise in trophic level is called biomagnification.

Long Answer Questions

Question 1.
(a) What is ozone ? How is it formed in the atmosphere ? Explain with equation.
(b) How is ozone layer useful ?
(c) Name the substances responsible for the depletion of ozone layer. (CCE 2013)
Answer:
(a) Ozone is triatomic form of oxygen, O₃. Ozone is formed in the upper atmosphere by the action of ultraviolet (UV) radiations over oxygen (O₂)

(b) The important ozone depleting substances or ODS are chlorofluorocarbons (CFC), methane, N₂O, chlorine, halons and carbon tetrachloride.

Question 2.
(a) What are trophic levels in a food chain ?
(b) Explain the flow of energy through food chain.
(c) Write a four trophic level food chain and represented in the form of an ecological pyramid. (CCE 2013)
Answer:
(a) Trophic Levels. They are steps or divisions of food chain which are characterised by particular methods of obtaining food, e.g., producers (T₁), herbivores (T₂), primary carnivores (T₃), etc.

(b) Flow of Energy Through Food Chain. Energy enters a food chain through producers. Producers or green plants trap solar energy and convert it into chemical energy of food during photosynthesis. From producers energy passes into herbivores. A lot of energy dissipates during transfer and utilization of food energy by herbivores (10% law). From herbivores the food energy passes into primary carnivores, again with a lot of dissipation. Only about 10% of herbivore energy is passed into body mass of primary carnivores. From primary carnivores, nearly 10% energy passes into secondary carnivores and so on. It is ultimately lost as heat.

(c) Aquatic Four Trophic Level Food Chain.
Phytoplankton ———> Zooplankton ———> Small Carnivorous Fish ———> barge Carnivorous Fish.

Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 15 Our Environment are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 2 Acids Bases and Salts Class 10 Science Important Questions and Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Acids Bases and Salts Class 10 Important Questions and Answers Science Chapter 2

Very Short Answer Questions

Question 1.
Give the names and formulae of two
(i) strong monobasic acids
(ii) two weak dibasic acids.
Answer:
(i) hydrochloric acid (HCl), nitric acid (HNO₃)
(ii) carbonic acid (H₂CO₃), oxalic acid (C₂H₂O₄).

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
How will you show that acetic acid is a monobasic acid ?
Answer:
When acetic acid is reacted with sodium hydroxide solution, only one H atom of the acid gets replaced and the product is sodium acetate and water. This shows that acetic acid is a monobasic acid.

Question 3.
Why alkalies like sodium hydroxide and potassium hydroxide should not be left exposed to air ?
Answer:
Because they are hygroscopic in nature and absorb moisture from atmosphere in which they ultimately dissolve.

Question 4.
The pH of an aqueous solution decreases from 3 to 2. What will happen to the nature of the solution ?
Answer:
The acidic character of the solution will further increase.

Question 5.
What happens to the crystals of washing soda when exposed to air ?
Answer:
They undergo efflorescence. As a result, washing soda (Na₂CO₃.10H₂O) changes to washing powder (Na₂CO₃.H₂O).

Question 6.
State whether an aqueous solution of washing soda is acidic or alkaline.
Answer:
An aqueous solution of washing soda is alkaline (turns red litmus blue). On dissolving in water, it forms NaOH (strong base) and carbonic acid (weak acid).

Therefore, resulting solution is alkaline or basic in nature.

Question 7.
What is the chemical name and chemical formula of baking soda ?
Answer:
The chemical name of baking soda is sodium hydrogen carbonate or sodium bicarbonate. Its chemical formula is NaHCO₃.

Question 8.
When a few drops of phenolphthalein indicator were added to the solution of some compound A’, the solution became pink. What does it indicate ?
Answer:
This shows that the solution of compound A’ is of basic nature since phenolphthalein becomes pink in basic medium.

Question 9.
Which is a stronger acid ? A solution with pH 5 and a solution with pH 2 ?
Answer:
A solution with pH 2 is a stronger acid. In general, lesser the pH, more will be the acidic nature of the solution.

Question 10.
What is the nature of NaHCO₃ salt ?
Answer:
It is an acidic salt since it has still one replaceable hydrogen atom present.

Question 11.
Give two examples of the salts belonging to the chloride family.
Answer:
Sodium chloride (NaCl) and potassium chloride (KCl).

Question 12.
What will be the colour acquired by a basic solution if a few drops of indicator methyl orange are added to it ?
Answer:
The solution will acquire a yellow colour.

Question 13.
Name the gas evolved when dilute HCl reacts with sodium hydrogen carbonate. How is it recognised ?
Answer:
The gas evolved is carbon dioxide (CO₂). When the gas is bubbled through lime water, it becomes milky.

Question 14.
Arrange the following in increasing order of their pH values :
NaOH solution, blood, lemon juice
Answer:
Increasing order of pH values is : lemon juice < blood < NaOH solution

Question 15.
How does the pH change when the solution of base is diluted with water ?
Answer:
Upon diluting a solution of base with water, the number of OH’ ions in solution per unit volume decrease. The basic strength of the base decreases and pH of solution decreases.

Question 16.
Which one of these has a higher concentration of H⁺ ions ?
Answer:
IM HCl or IM CH₃COOH.
Although both the acid solutions have the same molar concentration (lM) in aqueous solution, but HCl will release more H+ ions as compared to CH₃COOH since it is a stronger acid.

Question 17.
Which bases are called alkalies ? Give an example of alkalies ?
Answer:
Water soluble bases are called alkalies. Sodium hydroxide (NaOH) is an example of alkalies.

Question 18.
Name the natural source of each of the following :
(a) Citric acid
(b) Oxalic acid
(c) Lactic acid
(d) Tartaric acid. (CBSE 2014)
Answer:
(a) Citrus fruits like lemons and oranges
(b) Tomatoes
(c) Milk
(d) Tamarind.

Question 19.
Write the name and chemical formula of the main product formed by heating baking soda.
Answer:
Baking soda is chemically sodium hydrogen carbonate (NaHCO₃). Upon heating, it forms sodium carbonate (Na₂CO₃) as the main product.

Question 20.
Write the names and chemical formulae of the products formed by heating gypsum at 373 K.
Answer:
Gypsum upon heating to 373 K forms Plaster of Paris and water

Question 21.
A student tested the pH of distilled water and found that the colour of pH paper changed to light green.
He found the pH again after dissolving a pinch of common salt in it. What will be colour of pH paper ?
Answer:
Distilled water is neutral with pH close to 7. An aqueous solution of common salt is also neutral. This means that there will be no change in the pH. The colour of pH paper will remain the same i.e., light green.

Question 22.
The pH of rain water collected from two cities A and B was found to be 6 and 5 respectively. The water of which city is more acidic ?
Answer:
Rain water of city B with pH 5 is more acidic.

Question 23.
Why does an aqueous solution of alcohol fail to conduct electric current ?
Answer:
An aqueous solution of alcohol fails to conduct electric current since it does not release H⁺ ions in solution.

Question 24.
Name the chemical substance which constitutes bees sting.
Answer:
It is methanoic acid or formic acid (HCOOH).

Question 25.
Which substance constitutes the enamel coating of our teeth ?
Answer:
Calcium phosphate Ca₃(PO₄)₂ constitutes the enamel coating of our teeth.

Question 26.
What happens when a base reacts with a non-metallic oxide. What would you infer about the nature of the non-metallic oxide ?
Answer:
A base reacts with a non-metal oxide to form salt and water. The non-metal oxide is, therefore, an acidic oxide. For example.
2 NaOH (aq) CO₂ (g) ———> Na₂CO₃ (aq) + H₂O (aq) .

Question 27.
Name the acids and bases from which the following salts may be obtained.
(i) Potassium sulphate
(ii) Calcium chloride
Answer:
(i) Potassium hydroxide (KOH), Sulphuric acid (H₂SO₄)
(ii) Calcium hydroxide Ca(OH)₂, Plydrochioric acid (HCl)

Question 28.
What will be the pH of the following salt solutions.
(i) Salt made from strong acid and strong base.
(ii) Salt made from strong acid and weak base.
Answer:
(i) The solution will be neutral with pH close to 7 (e.g. NaCl).
(ii) The solution will be acidic with pH less than 7 (e.g. NH₄Cl).

Question 29.
Give examples of two substances having water of crystallisation. Write their formulae also.
Answer:
Blue vitriol or hydrated copper sulphate : CuSO₄. 5H₂O.
Green vitriol or hydrated ferrous sulphate : FeSO₄. 7H₂O.

Question 30.
What are the pH values of distilled water and common salt solution ?
Answer:
Both are neutral and have pH close to 7.

Question 31.
Which one is a stronger acid, with = 5 or with pH = 2 ?
Answer:
The acid with pH = 2 is a stronger acid.

Question 32.
The pW of three solutions A, B and C are 4, 9 and 6 respectively. Arrange them in increasing order of acidic strength.
Answer:
The increasing order of acidic strength is : B < C < A.

Short Answer Questions

Question 33.
How will you find pH of lemon juice ?
Answer:
(a) Take about 5mL of the given sample of lemon juice in a test tube.
(b) Dip a strip of the universal pH paper in the tube.
(c) Take out the strip and note its colour. It will acquire a orange red colour.
(d) On comparison with pH paper chart, the pH of the solution falls in the range between 2 and 3.

Question 34.
A sample of bleaching powder was kept in an air tight container. After a month, it lost some of its chlorine content. How will you account for it ?
Answer:
Bleaching powder if kept even in an air tight container, will slowly decompose of its own and form calcium chlorate and calcium chloride. The reaction is called auto-oxidation. This will result in decrease in its chlorine contents.

Question 35.
An aqueous solution of sodium carbonate is basic and not acidic. Assign reason.
Answer:
Sodium carbonate reacts with water to form sodium hydroxide and carbonic acid.

Since the base is strong while acid is weak, the solution is basic and not acidic.

Question 36.
An old person complained of acute pain in the stomach. Doctor gave him a small antacid tablet and he got immediate relief. What actually happened ?
Answer:
The old person was suffering from acute acidity. Antacid tablet contains sodium hydrogen carbonate (NaHCO₃). It reacts with the acid (HCl) formed because of acidity and neutralizes its effect. That is how the old person got relief.

Question 37.
A milkman adds very small amount of baking soda to fresh milk. What happens to its pW ?
Answer:
The pH of fresh milk is nearly 6. Baking soda is sodium hydrogen carbonate (NaHCO₃). On adding it to fresh milk, the medium becomes alkaline and its pH therefore, increases.

Question 38.
A few drops of phenolphthalein indicator were added to an unknown solution A. It acquired pink colour. Now another unknown solution B was added to it dropwise and the solution ultimately became colourless. Predict the nature of the solutions A and B.
Answer:
The solution A is basic in nature and phenolphthalein has imparted pink colour to it. The solution B is of an acid which has ultimately made solution A colourless by neutralising its basic effect.

Question 39.
A compound which is prepared from gypsum has the property of hardening when mixed with proper quantity of water. Identify the compound. Write chemical equation to prepare the compound. Mention one important use of the compound.
Answer:
The compound is Plaster of Paris (CaSO₄.½ H₂O). It is formed from Gypsum (CaSO₂.2H₂O) upon heating to a temperature of 373 K and also changes back to Gypsum on adding water. Plaster of Paris is used for setting fractured bones.

Question 40.
The oxide of a metal M was water soluble. When a blue litmus strip was dipped in this solution, it did not undergo any change in colour. Predict the nature of the oxide.
Answer:
The metal oxide (MO) is of basic in nature. It dissolves in water to form metal hydroxide as follows :
MO + H₂O ———-> M(OH)₂
A blue litmus does not undergo any change in colour in the basic medium.

Question 41.
Does tartaric acid help in making cake or bread fluffy ? Explain.
Answer:
No, tartaric acid with the formula CH(OH)COOHCH(OH)COOH does not evolve any carbon dioxide during baking. Its role is to react with Na₂CO₃ formed when NaHCO₃ decomposes.

If it is not done, Na₂CO₃ will impart a bitter taste to the cake.

Question 42.
A doctor applied surgical bandages on the fractured bones of changes are likely to occur ?
Answer:
Surgical bandages are made from Plaster of Paris. When applied on the fractured bones after making them wet, it changes into a hard mass called Gypsum.

The hard mass keeps the bones in proper position and the gap is slowly filled because of calcification that is taking place on the broken parts. This helps in uniting broken bones and they change to a single piece again.

Question 43.
A chemical compound having smell of chlorine is used to remove yellowness of white clothes in laundries. Name the compound and write the chemical equation involved in its preparation.
Answer:
The compound is bleaching powder (CaOCl₂). It removes yellowness from clothes due to its bleaching action. For chemical equation,

Question 44.
Explain giving reasons :
(i) Tartaric acid is a component of baking powder used in making cakes.
(ii) Gypsum, CaSO₄.2H₂O is used in the manufacture of cement.
Answer:
(i) Role of tartaric acid in baking powder (mixture of tartaric acid and sodium hydrogen carbonate) is to neutralise sodium carbonate formed upon heating sodium hydrogen carbonate.

In case it is not done, cake will be bitter and sodium carbonate will also have injurious side effects.
(ii) The role of gypsum (CaSO₄.2H₂O) in the manufacture of cement is to slow down the process of setting of cement.

Question 45.
What happens when crystals of washing soda are exposed to air ?
Answer:
Washing soda undergoes efflorescence and as a result loses nine molecules of water to form white powder.

Question 46.
How is chloride of lime chemically different from calcium chloride ? Why does chloride of lime gradually lose its chlorine when kept exposed to air ?
Answer:
Chloride of lime is calcium oxy chloride [(Ca(OCl)Cl] also known as bleaching powder. Calcium chloride is CaCl₂. Bleaching powder loses its chlorine on exposure to air because CO₂ present in air reacts with it to evolve chlorine as follows :

Question 47.
State the chemical property in each case on which the following uses of baking soda are based :
(i) as an antacid.
(ii) as a constituent of baking powder.
Answer:
(i) It is weakly alkaline in nature and neutralizes acid (HCl) formed in the stomach.
NaHCO₃ + HCl ———-> NaCl + H₂O + CO₂
(ii) It evolves CO₂ in the form of bubbles when cake is made by baking. As a result, the cake becomes porous as well as fluffy.

Question 48.
Crystals of copper sulphate are heated in a test tube for some time.
(a) What is the colour of copper sulphate crystals (i) before heating (ii) after heating ?
(b) What is the source of liquid droplets seen on the inner upper side of the test tube during the heating process ?
Answer:
(a) Colour of crystals before heating : blue.
Colour of crystals after heating : white.
(b) The liquid droplets formed in the inner upper side of the test tube during the heating process are of water. It is released from the crystals of copper sulphate during heating.

Question 49.
A knife, which is used to cut a fruit, was immediately dipped into water containing drops of blue litmus solution.
If the colour of the solution is changed to red, what inference can be drawn about the nature of the fruit and why ?
Answer:
Since the colour of the blue litmus has changed to red, this means that the fruit juice is acidic in nature.

Question 50.
A person is suffering from indigestion due to the intake of hot spicy food. What remedy you will prescribe to the patient ?
Answer:
Give the name of a chemical that can give relief to him.
The spicy food has resulted in acidity in the stomach. An antacid is needed to cure it. Magnesium hydroxide Mg(OH)₂ acts as an antacid.

Question 51.
(a) Give the chemical names of acids present in :

1. ants
2. lemon
3. milk
4. tomato.

(b) Write the chemical names of two salts belonging to sodium family.
Answer:
(a)

1. Methanoic acid (Formic acid)
2. Citric acid
3. Lactic acid
4. Oxalic acid.

(b) Sodium chloride (NaCl) and Sodium nitrate (NaNO₃).

Long Answer Questions

Question 52.
(a) A solution has a pH of 7. Explain how you would you :
(i) increase its pH
(ii) decrease its pH
(b) If a solution changes the colour of the litmus from red to blue, what can you say about its pH ?
(c) What can you say about the pH of a solution that liberates carbon dioxide from sodium carbonate ?
Answer:
(a) The solution with pH 7 is neutral. Its pH can be increased by adding a small amount of base like sodium hydroxide. Basic solutions have pH more than 7. Similarly, pH can be decreased by adding small amount of acid like hydrochloric acid. Acidic solutions have pH less than 7.
(b) The change in colour of litmus from red to blue indicates that the solution is of basic nature with pH more than 7.
(c) Carbon dioxide can be liberated by reacting sodium carbonate solution with acid like dilute hydrochloric acid. This shows that the solution is of acidic nature with pH less than 7.

Question 53.
Explain why :
(i) Common salt becomes sticky during the rainy season
(ii) Blue vitriol changes to white upon heating
(iii) If bottle full of concentrated sulphuric acid is left open in the atmosphere by accident, the acid starts flowing out of the bottle of its own.
Answer:
(i) Common salt contains the impurity of magnesium chloride (MgCl₂) which is of deliquescent nature. When exposed to atmosphere, it becomes moist. Therefore, common salt becomes sticky during the rainy reason.
(ii) Blue vitriol (CUSO₄.5H₂O) upon heating changes to anhydrous copper sulphate (CUSO₄) which is white in colour.
(iii) Concentrated sulphuric acid is highly hygroscopic. It absorbs moisture from air and gets diluted. Since the volume increases, the acid starts flowing out of the bottle.

Question 54.
(a) Name the raw materials used in the manufacture of sodium carbonate by Solvay process.
(b) How is sodium hydrogen carbonate formed during Solvay process separated from a mixture of NH₄Cl and NaHCO₃ ?
(c) How is sodium carbonate obtained from sodium hydrogen carbonate ?
Answer:
(a) The raw materials used are : NaCl, lime stone or CaCO₃ and NH₃.
(b) Sodium hydrogen carbonate (NaHCO₃) is sparingly soluble or less soluble in water and gets separated as a preciptate while NH₄Cl remains in solution. The precipitate is removed by filtration.
(c) Sodium hydrogen carbonate is converted to sodium carbonate upon heating.

Question 55.
(a) What is the action of red litmus on

1. dry ammonia gas
2. solution of ammonia gas in water ?

(b) State the observations you would make on adding ammonium hydroxide to aqueous solution of

1. ferrous sulphate
2. aluminium chloride.

Answer:
(a)

1. Red litmus has no action on dry ammonia gas because it does not release any hydroxyl ions (OH)^–
2. When passed through water, ammonia (NH₃) is converted to ammonium hydroxide (NH₄OH). It dissociates to give hydroxyl ions (OH)^– and the solution is basic in nature. Red litmus acquires a blue colour.

(b)

1. A green precipitate of ferrous hydroxide would be formed by double displacement reaction.
   
2. A white precipitate of aluminium hydroxide will be formed by double displacement reaction.
   

Question 56.
(a) Why does an aqueous solution of an acid conduct electricity ?
(b) How does the concentration of hydrogen ions [H₃O]⁺ change when the solution of an acid is diluted with water ?
(c) Which has a higher pH value ; a concentrated or dilute solution of hydrochloric acid ?
(d) What would you observe on adding dilute hydrochloric acid to

1. sodium bicarbonate placed in a test tube ?
2. zinc metal in a test tube ?

Answer:
(a) An aqueous solution of an acid conducts electricity because in water, an acid (e.g. HCl) dissociates to give ions. Since the current is carried by the movement of ions, an aqueous solution of acid conducts electricity.
(b) Upon dilution, more of acid dissociates into ions. Therefore, concentration of [H₃O]⁺ ions increases upon dilution.
(c) Although more [H₃O]⁺ ions are formed upon dilution, but the number of ions per unit volume decrease. Therefore, pH will increase upon dilution.
(d)

1. Carbon dioxide gas would evolve accompanied by brisk effervescene.
   NaHCO₃ (s) + HCl (aq) ———–> NaCl(aq) + CO₂(g) + H₂O(aq)
2. Hydrogen gas would evolve accompanied by brisk effervescene.
   Zn(s) + 2HCl (aq) ———–> ZnCl₂(ag) + H₂(g)

Question 57.
(a) A gas is produced when cone. H₂SO₄ is added to solid sodium chloride taken in a test tube and the tube is heated. The gas coming out through the delivery tube is passed over a dry litmus paper and then over a moist litmus paper. What would you observe ? Explain your answer,
(b) Fresh milk has pH of 6. When it changes to curd (yogurt), will its pH value increase or decrease ? Why ?
(c) What will be the colour of blue litmus in a solution of sodium carbonate ?
Answer:
(a) Upon heating sodium chloride with cone. H₂SO₄, hydrogen chloride gas evolves.
NaCl(s) + H₂SO₄(aq) ———> NaHSO₄ (aq) + HCl (g)
In the gaseous state, the acidic character is not shown because HCl does not release any H⁺ ions. In the presence of moisture (moist litmus paper), the gas changes to hydrochloric acid i.e., HCl(aq). The acid releases H⁺ ions and thus, shows acidic character. Therefore, moist blue litmus paper becomes red.
(b) When fresh milk changes to curd, the pH of the solution is likely to decrease. Actually, lactose present in milk gets converted to lactic acid when curd or yogurt is formed from milk. Therefore, the medium becomes more acidic and its pH decreases.
(c) The solution of sodium carbonate (Na₂CO₃) is of basic nature. Actually, the salt dissolves in water to produce NaOH (strong base) and H₂CO₃(weak acid). The blue litmus will not undergo any change in the basic medium. It will remain blue.

Question 58.
When electricity is passed through a common salt solution, sodium hydroxide is produced along with the liberation two gases ‘X’ and ‘Y’. The gas ‘X’ burns with a pop sound whereas ‘Y’ is used for disinfecting drinking water.
(i) Identify X and Y.
(ii) Give the chemical equation for the reaction stated above.
(iii) State the reaction of Y with dry slaked lime.
Answer:
(i) The gas ‘X’ is H₂ and gas ‘Y’ is Cl₂
(ii) The chemical equation for the reaction is :

(iii) Cl₂ reacts with slaked lime to form bleaching powder.
Ca(OH)₂ + Cl₂ ———–> CaOCl₂ + H₂O.

Question 59.
(i) What are strong acids and weak acids ? Give an example for each.
(ii) A dry pellet of a common base ‘B’ when kept in open absorbs moisture and turns sticky. The compound is also formed by Chloralkali process. Identify B. What type of reaction occurs when B is treated with dilute hydrochloric acid ? Write the chemical equation.
Answer:
(i) The strength of an acid is expressed in terms of its H⁺ ions releasing tendency in aqueous solution or in terms of its degree of dissociation
(α). Strong acids have large value of α (close to one) while weak acids have comparatively less value. For example, hydrochloric acid (HCl) is a strong acid while acetic acid (CH₃COOH) is a weak acid.
(ii) The available information suggests that the base ‘B’ present in the pellet is sodium hydroxide (NaOH). It is of deliquescent nature. It absorbs moisture from atmosphere and becomes sticky. The base reacts with dilute hydrochloric acid to form salt and water. This reaction is known as neutralisation reaction.
NaOH (aq) + HCl(aq) ———–> NaCl (aq) + H₂O(l)

Question 60.
Write the chemical name and formula of common salt. List two main sources of common salt in nature. Write any three uses of common salt. How is it connected to our freedom struggle ?
Answer:
Sodium chloride (NaCl) also called common salt or table salt is the most essential part of our diet. Chemically it is formed by the reaction between solutions of sodium hydroxide and hydrochloric acid. Sea water is the major source of sodium chloride where it is present in the dissolved form alongwith other soluble salts such as chlorides and sulphates of calcium and magnesium. It is separated by some suitable method. Deposits of the salt are found in different parts of the world and is known as rock salt. The formation of rock salt is due to the slow evaporation of sea water which takes ages. When pure, it is a white crystalline solid. However, it is often brown due to the presence of impurities.
• Sodium Chloride — Essential for Life
Sodium chloride is quite essential for life. Biologically, it has a number of functions to perform such as in muscle contraction, in conduction of nerve impulses in the nervous system and is also converted into hydrochloric acid in the stomach which helps in the digestion of food. When we sweat, there is loss of sodium chloride and some. Other salts alongwith water. This leads to muscle cramps. The loss has to be compensated suitably by giving certain salt preparations to the patients. These are called electrolytes Electral powder is a very popular electrolyte.
• Chemicals from Common Salt
Sodium chloride is also a very useful raw material for different chemicals. A few out of these are : hydrochloric acid (HCl), washing soda (Na₂CO₃-10H₂O), baking soda (NaHCO₃) etc. Upon electrolysis, a strong solution of the salt (brine), sodium hydroxide, chlorine and hydrogen are obtained.
Apart from these, it is used in leather industry for the leather tanning. In severe cold, rock salt is spread on icy roads to melt ice. It is also, a fertilizer for sugar beet.

Question 62.
State what happens when a concentrated solution of sodium chloride (brine) is electrolysed ? Name the process. Write the equation of the reaction involved. Write the names of the products obtained. Mention one use of each product.
Answer:
Sodium chloride (NaCl) also called common salt or table salt is the most essential part of our diet. Chemically it is formed by the reaction between solutions of sodium hydroxide and hydrochloric acid. Sea water is the major source of sodium chloride where it is present in the dissolved form alongwith other soluble salts such as chlorides and sulphates of calcium and magnesium. It is separated by some suitable method. Deposits of the salt are found in different parts of the world and is known as rock salt. The formation of rock salt is due to the slow evaporation of sea water which takes ages. When pure, it is a white crystalline solid. However, it is often brown due to the presence of impurities.
• Sodium Chloride — Essential for Life
Sodium chloride is quite essential for life. Biologically, it has a number of functions to perform such as in muscle contraction, in conduction of nerve impulses in the nervous system and is also converted into hydrochloric acid in the stomach which helps in the digestion of food. When we sweat, there is loss of sodium chloride and some. Other salts alongwith water. This leads to muscle cramps. The loss has to be compensated suitably by giving certain salt preparations to the patients. These are called electrolytes Electral powder is a very popular electrolyte.
• Chemicals from Common Salt
Sodium chloride is also a very useful raw material for different chemicals. A few out of these are : hydrochloric acid (HCl), washing soda (Na₂CO₃-10H₂O), baking soda (NaHCO₃) etc. Upon electrolysis, a strong solution of the salt (brine), sodium hydroxide, chlorine and hydrogen are obtained.
Apart from these, it is used in leather industry for the leather tanning. In severe cold, rock salt is spread on icy roads to melt ice. It is also, a fertilizer for sugar beet.

 

 

Hope given Previous Year Question Papers for CBSE Class 10 Science Chapter 2 Acids, Bases and Salts are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

Chapter 3 Metals and Non-metals Class 10 Science Important Questions and Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Metals and Non-metals Class 10 Important Questions and Answers Science Chapter 3

Very Short Answer Questions

Question 1.
Name the metal which is most abundant in earth’s crust.
Answer:
Aluminium (Al) is the most abundant metal in the earth’s crust and is present to the extent of 8-1 per cent by mass.

More Resources

• Previous Year Question Papers for CBSE Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science

Question 2.
What is the difference between calcination and roasting ?
Answer:
Calcination is carried in the absence of air while roasting is done in excess of air.

Question 3.
What is the chemical formula of rust ?
Answer:
Rust is hydrated ferric oxide and its chemical formula is Fe₂O₃.xH₂O.

Question 4.
Name the process used for the enrichment of sulphide ore.
Answer:
The process is called Froth Floatation process.

Question 5.
Out of zinc and iron, which evolves hydrogen more readily on reacting with dilute HCl ?
Answer:
Zinc evolves hydrogen more readily than iron on reacting with dilute HCl because it is placed above iron in the reactivity series.

Question 6.
How do alloys brass and bronze differ in composition ? (CBSE 2010)
Answer:
Constituents of brass are copper and zinc while those of bronze are copper and tin.

Question 7.
Does german silver contain silver in it ?
Answer:
German silver is an alloy of copper, zinc and nickel. It does not contain any silver in it.

Question 8.
Write the chemical formulae of the main ores of iron and aluminium.
Answer:
The main ore of iron is haematite (Fe₂CO₃) while that of aluminium is bauxite (Al₂O₃.2H₂O).

Question 9.
Name the non-metal which can conduct electricity.
Answer:
Graphite, an allotropie form of carbon conducts electricity.

Question 10.
Write the names of two neutral oxides. (CBSE 2010)
Answer:
Two neutral oxides are : carbon monoxide (CO) and nitrous oxide (N₂O).

Question 11.
Name the chemical formula of zinc blende and galena.
Answer:
Zinc blende is zinc sulphide (ZnS) while galena is lead sulphide (PbS).

Question 12.
Write one example each of :

1. a metal having low melting point and a metal having high melting point.
2. a metal which is a poor conductor of electricity and a non-metal which is a good conductor of electricity.

Answer:

1. Gallium (Ga) is a metal with very low melting point (302 K). Diamond (carbon) is a non-metal with very high melting point. (4000 K)
2. Metal lead (Pb) is a poor conductor of electricity whereas graphite (carbon) is a good conductor of electricity.

Question 13.
Which acts as anode in the electro-refining of metals ?
Answer:
A plate of impure metal acts as anode in the electro-refining of metals.

Question 14.
What is the name of the bond formed when a metal atom combines with the atom of a non-metal ? (CBSE 2010)
Answer:
Bond formed is ionic or electrovalent.

Question 15.
How will you account for the high melting points of salts ?
Answer:
The high melting points of salts are due to their closely packed structures and also due to stronger forces of attraction in the oppositely charged ions.

Question 16.
Name two metals which exist in the native or free state.
Answer:
Metals gold (Au) and platinum (Pt) exist in the free or native state.

Question 17.
What reaction takes place when manganese dioxide is heated with aluminium powder ?
Answer:
3MnO₂(s) + 4Al(s) ————> 3Mn(l) + 2Al₂O₃(s)

Question 18.
Can rusting of iron nail occur in distilled water ?
Answer:
No, because distilled water has no dissolved oxygen in it.

Question 19.
Which metal is the best conductor of electricity ? (CBSE 2010)
Answer:
Silver (Ag) is the best conductor of electricity.

Question 20.
Which metal is used in amalgams ?
Answer:
Mercury (Hg) is used in amalgams that are also alloys in nature.

Question 21.
Why are metals conducting in nature ?
Answer:
The conductivity of metals is due to the movement of electrons. These are mobile even in the solid state.

Question 22.
Why do metals generally appear to be dull ?
Answer:
When metals are kept exposed to air for sometime, oxygen present in air slowly combines with the metal to form metal oxide. It is deposited as a layer on the surface of metals. They appear to be dull.

Question 23.
Name two non-metals which exist in the solid state and two non-metals which exist in the gaseous state.
Answer:
Solid State : Sulphur, phosphorus;
Gaseous state : Nitrogen, oxygen.

Question 24.
Name the metal whose foils are used for the packing of food materials.
Answer:
Aluminium foils are used for the purpose.

Question 25.
The electronic configuration of an elements ‘E’ (Z = 16) is 2, 8, 6. Will it lose six electrons or gain two electrons ?
Answer:
It will gain two electrons.

Question 26.
Alloys are used in electrically heating devices rather than pure metals. Give one reason.
(CBSE All India 2009)
Answer:
Alloys are generally the combination of two or more metals. Since metals are good conductors of electricity, a combination of metals i.e., alloy is expected to be a better conductor of electricity than the pure metal,

Question 27.
A shining metal ‘X’ on heating in air becomes black in colour. Name the black coloured compound formed and identify ‘X’.
Answer:
The black coloured compound is copper (II) oxide or cupric oxide. The metal ‘X’ is copper.

Question 28.
Why do silver articles become black after some time ?
Answer:
Traces of hydrogen sulphide (H₂S) gas are present in air/atmosphere. It slowly reacts with silver to form silver sulphide which is black. As a result, silver ornaments lose their shine after sometime.

Question 29.
Name a metal other than aluminium that is covered with a layer of oxide film.
Answer:
Iron (Fe) is also covered with a layer of its oxide (Fe₂O₃) when kept exposed to air for a long time.

Question 30.
What is the common feature in the electronic configuration of metal atoms ?
Answer:
The metal atoms in general have one, two or maximum of three valence electrons which they can easily lose to form cations or positive ions.

Question 31.
What are ionic compounds ?
Answer:
These are the compounds in which the constituent particles are ions (cation and anions) attracted to each other by strong forces of attraction.

Question 32.
Name one metal and one non-metal which exist in liquid state at room temperature ?
Answer:
Mercury (metal) and bromine (non-metal) exist as liquid at room temperature.

Question 33.
What changes do you observe in the iron nails and colour of copper sulphate solution if the nails are dipped in CuSO₄ solution for 15 minutes ?
Answer:
Iron nails turn to brown and the solution becomes light green.

Question 34.
What are amphoteric oxides ? Give an example.
Answer:
These are the oxides which act both as acids and bases. For example, zinc oxide (ZnO).

Question 35.
Name a non-metal which is lustrous and a metal which is non-lustrous.
Answer:
Bromine (non-metal) is lustrous. Sodium (metal) is non-lustrous due to the formation of an oxide layer on its surface.

Question 36.
Give the electronic configuration of an element having atomic number 11. (CBSE 2010)
Answer:
The element with atomic number (Z) 11 is sodium (Na). Its electronic configuration is 2, 8, 1.

Question 37.
Why are metals good conductors of electricity while non-metals are not ? (CBSE 2010, 2012)
Answer:
The metal atoms can easily release electrons to conduct electric current. The atoms of non-metals are not in a position to do so and therefore, are not conducting.

Short Answer Questions

Question 38.
Which important properties of aluminium are responsible for its great demand in industry ?
Answer:
The properties of aluminium metal responsible for its great demand in industry are :

1. The metal is a good conductor of electricity.
2. The metal is not attacked by water.
3. The metal is a powerful reducing agent.

Question 39.
Name an alloy of

1. Aluminium used in construction of air crafts.
2. Lead in joining metals for electric welding.
3. Copper used in household vessels.

Answer:

1. The alloy is duralumin : A1 (93%), Cu (4%), Mg (0.5%), Mn (0.5%).
2. The alloy is solder : Pb (50%), Sn (50%)
3. The alloy is brass : Cu (80%), Zn (20%)

Question 40.
All ores are minerals but all minerals are not ores. Justify.
Answer:
In the earth’s crust, metals are present in the form of minerals and there are more than one mineral for a particular metal. However, metal may not be extracted from all of them. The mineral from which a metal can be profitably and conveniently extracted is known as ore. This clearly means that all ores are minerals but all minerals are not ores. For example, the different minerals of iron are :
Haematite : Fe₂O₃ ;
Limonite : Fe₂O₃.3H₂O;
Siderite : FeCO₃ ;
Iron pyrites : FeS₂
Iron is extracted from haematite (Fe₂CO₃). Haematite mineral is the ore of iron while other minerals are not the ores.

Question 41.
(a) An iron knife kept in blue copper sulphate solution turns the blue solution into light green. Explain.
(b) An athlete won a bronze medal in a race competition. After some days, he found that the medal had lost its lustre due to the formation of a greenish layer on it. Name the metals present in the medal. What is the reason for the appearance of a greenish layer on its surface ?
Answer:
(a) Iron lies above copper in the activity series. This means that iron or iron knife will displace copper from copper sulphate solution. As a result of the reaction, ferrous sulphate will be formed and the solution will be light green in colour.

(b) The bronze medal is an alloy and the constituting metals are copper and tin.
The loss of lustre by the medal is due to the formation of a coating of green layer. This layer is at basic copper carbonate.

Question 42.
Why is titanium called a strategic metal ? Mention two of its properties which make it so special.
Answer:
Titanium is called strategic metal because it is used for making certain war equipments. The properties which make the metal so special are :

1. It is light in weight but at the same time stronger than the other metals.
2. It is not affected by corrosion even if kept in the open for a very long time.

Question 43.
A copper plate was dipped into a solution of AgNO₃. After sometime, a black layer was deposited on the copper plate. State the reason for it. Write the chemical equation for the reaction involved.
Answer:
Copper lies above silver in the activity series. This means that copper is more reactive than silver. Therefore, copper had replaced silver from AgNO₃ solution. Silver got deposited on the copper plate and changed to black after sometime because silver and also some salts of silver are sensitive to light. They readily become blackish on standing or on exposure to air.

Question 44.
On placing a piece of zinc metal in a solution of mercuric chloride, it acquires a silvery surface but when it is placed in a solution of magnesium sulphate, no change is observed. State the reason for the behaviour of zinc metal.
Answer:
Zinc lies above mercury in the activity series and can easily replace it from mercuric chloride solution. Mercury formed in the reaction gets deposited on the surface of zinc to give it a silvery look.

But zinc is placed below magnesium in the activity series. Therefore, no chemical reaction occurs between zinc and magnesium sulphate solution.

Question 45.
Which method of concentration of ore is preferred in the following cases and why ?

1. The ore has higher density particles mixed with a large bulk of low density impurities.
2. The ore consists of copper sulphide intermixed with clay particles.
   Give an example of amalgam.

Answer:

1. The concentration of ore can be done by gravity separation method.
2. The concentration of ore is done by Froth Floatation process.
   An amalgam of mercury with silver or gold called dental alloy is used to fill cavities in the teeth.

Question 46.
Name an ore of zinc other than zinc oxide. By which process can this ore be converted into zinc oxide ?
Answer:
The ore of zinc other than zinc oxide (zincite) is zinc carbonate (calamine). It has the formula ZnCO₃ Calamine is converted into zinc oxide by calcination i.e., by heating strongly in the absence of air.

Question 47.
Give reasons for the following :
Metals replace hydrogen from dilute acids whereas non-metals do not. (CBSE 2011)
Answer:
Metals are electropositive in nature. Their atoms readily lose electrons to form positive ions. The electrons are accepted by H⁺ ions of the acid to evolve hydrogen gas. For example,
Zn(s) ———-> Zn²⁺(aq) + 2e^– ;
2H⁺(aq) + 2e^– ————> H₂(g)
Non-metals are electronegative in nature. This means that their atoms can take up electrons and cannot lose them. Therefore, they do not evolve hydrogen on reacting with dilute acids.

Question 48.
(a) Why is ZnO called an atmospheric oxide? Name another atmospheric oxide?
(b) Whar are alkalies? Give one exampleof alkalies?
Answer:
(a)

Aluminium oxide (Al₂O₃) is another amphoteric oxide.
(b) Water soluble hydroxides of metals are known as alkalis. For example, NaOH.

Question 49.
(a) What is the activity series of metals ? Arrange the metals Zn, Mg, Al, Cu and Fe in a decreasing order of reactivity.
(b) What would you observe when you put

1. some zinc pieces into blue copper sulphate solution ?
2. some copper pieces into green ferrous sulphate solution ?

(c) Name a metal which combines with hydrogen gas. Name the compound formed.
Answer:
(a) We find that zinc occupies a much higher position in the acitivity series as compared to copper. It is expected to displace copper present in the aqueous solution of its salt (e.g. CuSO₄).

(b)

1. Blue colour of copper sulphate solution would slowly disappear.
2. No change would be noticed.

(c) Sodium combines with hydrogen to form sodium hydride.

Question 50.
(a) Are all pure liquids bad conductors of electricity ?
Name a liquid which is a good conductor of electricity but does not undergo electrolysis on passing electric current.
If pure water is used, no electrolysis takes place. Why ?
Answer:
Name one practical application based on the phenomenon of electrolysis.
No, there are exceptions also. Mercury in pure state a good conductor of electricity.
Mercury is a good conductor of electricity but does not undergo electrolysis.
Pure water (H₂O) does not dissociate into ions on passing electric current.

Question 51.
What is the main ore of mercury ? How is mercury obtained by this ore?
Answer:
The main ore of mercury is cinnabar (HgS). Mercury is obtained from it by heating with excess of air or oxygen.

Question 52.
(a) Using a simple experiment, how can you prove that magnesium is placed above zinc in the reactivity ?
(b) Why cannot copper metal liberate hydrogen on reacting with dil. HCl ?
Answer:
(a) In a glass tube, take about 10 mL of aqueous solution of zinc sulphate. It is colourless. Dip a small and dry piece of magnesium ribbon in the solution. It slowly dissolves and greyish mass gets deposited at the bottom of the tube. This shows that magnesium is more reactive than zinc or it is placed above zinc in the activity series.

(b) Copper lies below hydrogen in the reactivity series and cannot lose electrons to H⁺ ions of the acid. This means that hydrogen gas cannot be liberated.

Question 53.
The way metals like sodium, magnesium and iron react with air and water, is an indication of their relative positions in the ‘reactivity series’. Is this statement true ? Justify your answer with examples. (CBSE 2014)
Answer:
Yes, the statement is true. We can have an idea about the relative positions of these metals in the reactivity series. For example,
(a) Sodium reacts violently even with cold water and with air or oxygen it readily combines.
(b) Magnesium reacts with hot water and with air or oxygen upon heating.
(c) Iron reacts with steam only and with air it reacts very slowly
This shows that the relative positions of these metals in the activity series are : sodium, magnesium, iron.

Question 54.
Metallic compound A reacts with dilute hydrochloric acid to produce effervescence and a gas B. The gas B extinguishes a burning candle and also turns lime water milky. Identify A and B. Write balanced chemical equations for the reactions involved.
Answer:
The available information suggests that the gas B is CO₂ since it turns lime water milky. The compound A is the carbonate or bicarbonate of some metal (e.g. calcium earbonate) The equations for the reactions involved are given :

Question 55.
Identify the oxides from the following which turn blue litmus into red.
CO₂, Na₂O, CaO, SO₂, NO₂.
What is the nature of these oxides ?
Answer:
These are the oxides of non-metals and are CO₂, SO₂ and NO₂. These are called acidic oxides since they form acids when dissolved in water. Their aqueous solution in water turns blue litmus red.

Question 56.
Name the chemical compounds formed on the surface of silver, copper and iron metals when exposed for sometime to atmosphere.
Answer:

1. On the surface of silver : Black silver sulphide (Ag₂S).
2. On the surface of copper : Green basic copper carbonate (Cu(OH)₂-CuCO₃)
3. On the surface of iron : Brown rust i.e., Hydrated ferric oxide (Fe₂O₃.xH₂O).

Long Answer Questions

Question 57.
When the powder of a common metal is heated in an open china dish, its colour turns black. However, when hydrogen gas is passed over the hot black substance formed, it regains its original colour. Based on this information, answer the following questions :

1. What type of chemical reaction takes place in each of the two given steps ?
2. Name the metal initially taken in the powder form. Write balanced chemical equations for both these reactions.

Answer:

1. The available information suggests the metal is copper. In open air, its is oxidised to form copper (II) oxide which is black in colour. The reaction is known as oxidation reaction. On passing hydrogen gas over the hot substance, the original colour of the metal is regained. It is an example of reduction reaction.
2. The balanced chemical equations for the reactions are :
   

Question 58.
(a) Which of the following metals would give hydrogen when added to dilute hydrochloricacid?

1. iron
2. copper
3. magnesium ?

(b)Explain why do surfaces of some metals acquire a dull appearance when exposed to air for a long lime.
Answer:
(a) Both iron (Fe) and magnesium (Mg) will evolve hydrogen on reacting with dilute hydrochloric acid. These are active metals and are placed above hydrogen in the activity series. As copper is placed below hydrogen in the series, it will not evolve hydrogen.
(b) Surfaces of some metals acquire a dull appearance when exposed to air for a long time and they lose their lustre. This is due to the formation of layer of oxides, hydroxides, carbonates etc. on the surface For example, surface of aluminium metal becomes dull white due to the formation of coating oi aluminium oxide (Al₂O₃). Similarly, the surface of copper acquires a greenish colour since a layer oi basic copper carbonate with the formula Cu(OH)₂CuCO₃ is deposited on the surface.

Question 59.
How will your demonstrate that the ionic compounds do not conduct electricity in the solid state and can do so in solution.
Answer:

1. In a glass beaker, take small amount of solid sodium chloride.
2. Dip two graphite rods (electrodes) in the solution.
3. Connect these rods to a battery through a bulb and a switch.
4. Switch on the battery. The bulb will not glow. This show that no current has passed through the solid sodium chloride.
5. Now, add some water to the salt so that it may dissolve.
6. Repeat the operation. The bulb will immediately glow showing that current has passed through the salt solution.
   

Explanation: Sodium chloride (NaCl) is a crystalline solid and the current is carried by the mobility (movement) of ions. Since the ions do not move in the solid state, the salt is not conducting. In aqueous solution, both Na+ and Cl- ions can move and the salt will be conducting in the solution. That is why the bulb glows.

Question 60.
With a suitable activity show that sulphur burns in air to form a compound which is acidic in nature.
Answer:

1. Take a small amount of sulphur powder on a spatula.
2. Now burn this powder by placing a tube in a inverted position over the spatula as shown in the figure.
3. The fumes produced as a result of burning of sulphur will get collected in the tube.
4. Place the tube in vertical position and immediately add some water to it.
5. Shake the tube so that the fumes may completely dissolve.
6. Add a few drops of blue litmus to a portion of the solution. It will acquire red colour which shows that it is of acidic nature.
7. To another portion, add a few drops of red litmus solution. No colour change will be noticed. This shows that the solution is not acidic.
   

Explanation : Sulphur burns in air to form sulphur dioxide which escapes from the tube as fumes with pungent and suffocating smell. The gas produced readily dissolves in water to form sulphurous acid (H₂SO₃). The solution is therefore, acidic. It will change the colour of blue litmus to red.

Question 61.
(a) Define corrosion; what is the nature given to corrosion of iron ?
(b) Name the colour of coating formed on silver and copper when exposed to air.
(c) List two damages caused by corrosion and suggest, how these can be prevented.
Answer:
(a) For definition of corrosion: The process of slow eating up of a metal by the gases and water vapours present in air due to formation of certain chemical compounds. Corrosion of iron is known as rusting.
(b) Coating deposited on the surface of silver metal is of silver sulphide (Ag₂S). It is black in colour. The coating deposited on copper surface is of basic copper carbonate Cu(OH)₂CuCO₃. It is green in colour.

(c) Corrosion of metals particularly the rusting of iron is very harmful. The structures made from iron are generally placed in the open. These are slowly corroded or rusted. This reduces their strength gradually. They become prone to accidents and are therefore, quite dangerous. A lot of care and money is involved in their maintenance. However, corrosion of aluminium has advantage. The metal placed high in the activity series is quite reactive. It combines with the oxygen present in air to form aluminium oxide (Al₂O₃).

Question 62.
Give reasons for the following :

1. Zinc can displace copper from copper sulphate solution.
2. Silver articles become black after sometime when exposed to air.
3. A metal sulphide is converted to its oxide to extract the metal from sulphide ore.

Answer:

1. Zinc is placed above copper in the activity series. Therefore, it can easily displace copper from copper sulphate solution.
   Zn(s) + CuSO₄(aq) ————> ZnSO₄(aq) + Cu(s)
2. Air contains traces of hydrogen sulphide (H₂S) gas. Silver has a tendency to combine with H₂S to form silver sulphide (Ag₂S) which is black in colour. On account of this, silver articles become black after some time when kept exposed to air.
3. A metal sulphide is normally converted into oxide by heating with excess of air or oxygen. This process is called roasting. Actually, the oxide of metal which is formed cap be easily reduced to the metallic form by reduction with carbon or some electropositive element. For example,
   

Question 63.
(a) Distinguish between ‘roasting’ and ‘calcination’. Which of the two is used for sulphide ores and why ?
(b) Write a chemical equation to illustrate the use of aluminium for joining cracked railway lines.
(c) Name the anode, the cathode and the electrolyte used in the electrolytic refining of impure copper.
Answer:
(a) For distinction between calcination and roasting,

Calcination	Roasting
(i) Calcination is carried in absence of air or oxygen.	Roasting is carried in the presence of excess of air.
(ii) As a result of calcination, the carbonate ore is converted to the oxide form.	As a result of roasting, the sulphide ore is converted to the oxide form.
ZnCO3(s) —— > ZnO(s) + CO2(g)	2ZnS(s)+3O2(g)—– > 2ZnO(s)+2SO2(g)

For the sulphide ores, the process of roasting is commonly used. It is carried by heating the ore helow its melting point with excess of air. As a result, the sulphide ore is converted to its oxide form. For example,

(b) Cracked railway lines can be joined or welded with the help of thermit welding. Thermit is a mixture of ferric oxide and aluminium powder. The chemical equation involved is :

(c) In the electrolytic refining of copper ;
Anode : A rod of impure copper.
Cathode : A rod of pure copper.
Electrolyte : An aqueous solution of copper sulphate containing a small amount of sulphuric acid.

Question 64.
(a) Give an example of a metal which

1. is a liquid at room temperature.
2. is kept immersed in kerosene for storing.
3. is both malleable and ductile.
4. is the best conductor of heat.

(b) Name the process of obtaining a pure metal from an impure metal through electrolysis. Suppose you have to refine copper using this process, then explain with the help of a labelled diagram the process of purification, mentioning in brief the materials used as (i) anode (ii) cathode and (iii) electrolyte.
Answer:
(a)

1. Mercury (Hg) is liquid at room temperature :
2. Sodium (Na) is kept immersed in kerosene for storing.
3. Aluminium (Al) is malleable and ductile
4. Silver (Ag) is the best conductor of heat.

(b) The process is known as electro-refining. For the electro-refining of copper,
The conversion of a crude metal into pure metal is known as metal refining.
The refining can be done in a number of ways but the most common among these is the electro-refining and is discussed.
This method is commonly used for the purification of the metals like Cu, Ag, Zn, Ni etc. The impure metal is converted into a block which is made anode in an electrolytic cell in which a plate of pure metal acts as the cathode as shown in the Figure 3.16.
The electrolyte is the solution of the soluble salt of the same metal, preferably a double salt. On passing electric current, metal ions from the electrolyte are reduced to the metal which is deposited on the cathode. An equivalent amount of the pure metal from the anode gets oxidised and the metal ions (or cations) go into the solution. This keeps on till the whole of the metal from the anode dissolves and deposits on cathode, leaving behind impurities in the form of a mud called anode mud.

For example, in the electro-refining of crude copper, impure metal is made anode and a plate of pure copper acts as the cathode. These are connected through a battery in the external circuit as shown in the figure. The electrolyte is aqueous solution of copper sulphate containing a small amount of sulphuric acid. On passing current, the following changes occur.

Question 65.
(a) Write the balanced chemical equations for the extraction of copper metal from its ore. What is the reducing agent used ?
(b) Which reducing agent can be used in the extraction of metals placed at the top of the reactivity series ? Give the name of the process also.
(c) What is the chemical substance formed as green coating when copper reacts with atmospheric gases in moist conditions ?
Answer:
(a) Copper is isolated from its sulphide ore known as copper glance (Cu₂S) by heating with excess of air or oxygen.

Cuprous oxide (Cu₂O) acts as reducing agent and this process is known as auto-reduction.
(b) These metals (K, Na, Ca, Mg etc.) can be isolated by carrying out the process of electrolysis (electrolytic reduction) from their molten salts.
(c) The green coating is of basic copper carbonate. It is formed as follows :

Question 66.
(a) Which method will you use to reduce the following ? Explain by giving a suitable example.
(i) Oxides of less reactive metals
(ii) Oxides of moderately reactive metals
(iii) Oxides of highly reactive metals.
(b) The reaction between metal ‘X’ and Fe₂O₃ is highly exothermic and is used to join railway tracks.
(i) Identify metal ‘X’ and name the reaction.
(ii) Write the chemical equation of its reaction with Fe₂O
Answer:
(a) (i) Oxides of less reactive metals can be reduced either by auto-reduction or upon heating. For example,

(ii) Oxides of moderately reactive metals can be reduced with coke. This is known as smelting. For example,

Question 67.
(a) Most metals do not react with bases but zinc metal does. Suggest a reason. Write an equation for the reaction between Zn and NaOH.
(b) When a metal X is treated with cold water, it gives a base Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z.
Answer:
(a) We know that zinc oxide (ZnO) is of amphoteric nature. The metal zinc also behaves similarly. It reacts with both acids and alkalies. For example,

(b) Molecular mass of base Y = 40 Atomic mass of X = 40 – (16 + 1) = 23
The metal X is sodium (Na). The salt Y is NaOH and liberated gas Z is, hydrogen.

Question 68.
With reference to electrorefining of impure copper, answer the following :
(a) Draw a neat and labelled diagram required for the purpose of electrorefining.
(b) What is the electrolyte used ?
(c) Name the cathode and anode used.
(d) What happens at cathode and anode ?
Answer:
(a) For the labelled diagram,

(b) An aqueous solution of copper sulphate containing a small amount of sulphuric acid is used as the

 

 

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