Murali

NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 10
Chapter Name	Reaching the Age of Adolescence
Number of Questions Solved	9
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence

NCERT TEXTBOOK EXERCISES

Question 1.
What is the term used for chemical secretions of endocrine glands responsible for changes taking place in the body?
Answer.
The term used for secretions of endocrine glands is hormones, which are responsible for various changes taking place in the body.

Question 2.
Define adolescence.
Answer.
The period of life when the body undergoes changes, leading to reproductive maturity is called adolescence.

Question 3.
What is menstruation? Explain.
Answer.
When the uterus receives the egg and it is fertilized, pregnancy occurs. If fertilization does not occur, the released egg and the thickened lining of the uterus along with its blood vessels are shed off: This causes bleeding in women, which is called menstruation.

Question 4.
List changes in the body that take place at puberty.
Answer.
The onset of puberty brings about:

1. Growth of the reproductive organs which begin to function.
2. Hair grows at various places of the body. Breasts develop in girls and facial hair (mustache and beard) appear in boys.
3. The voice of the boys becomes hoarse as the voice box enlarges during adolescence.

Question 5.
Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer.

Column A	Column B
Name of endocrine glands (i)Testes (ii)Ovaries	Name of hormones Testosterone (male) Estrogen (female)
Pituitary glands (iii)Thyroid (iv) Adrenal glands (v) Pancreas	Sex hormones and brain hormones Thyroxine Adrenalin Insulin

Question 6.
What are sex hormones? Why are they named so? State their function.
Answer.
Hormones secreted by testes and ovaries are termed as sex-hormones.

• They are named so because they are secreted by the reproductive organs.

Functions of sex-hormones.

• These hormones are responsible for the secondary sexual characters of males and females.

Question 7.
Choose the correct option.
(a) Adolescents should be careful about what they eat, because
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.
Answer.
(ii) proper diet is needed for the rapid growth taking place in their body. Reproductive age in women starts when their

(b) Reproductive age in women starts when their
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.
Answer.
(i) menstruation starts.

(c) The right meal for adolescents consists of
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.
Answer.
(ii) Chapati, dal, vegetables.

Question 8.
Write notes on:

1. Adam’s apple.
2. Secondary sexual characters.
3. Sex determination in the unborn baby.

Answer.

1. At puberty, the voice box or the larynx begins to grow. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple. This makes a boy’s voice hoarse.
2. In girls, breasts begin to develop at puberty and boys begin to grow facial hair, that is, mustaches and beards. As these features help to distinguish the male from the female, they are called secondary sexual characters.
3. Sex Determination in the Unborn Baby: All human beings have 1 pair of sex chromosomes, as the names X and Y. A female has two X chromosomes,

while male has one X and one Y chromosome. When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote, that will have ‘XT would develop into a male child. Now you know that the sex chromosomes of the father determine the sex of a baby.

Question 9.
Word game: Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone
Down
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through the bloodstream
6. Voicebox
7. Term for changes at adolescence.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 10 Reaching the Age of Adolescence, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes.

Board	CBSE
Textbook	NCERT
Class	Class 7
Subject	Science
Chapter	Chapter 6
Chapter Name	Physical and Chemical Changes
Number of Questions Solved	12
Category	NCERT Solutions

NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

Question 1.
Classify the changes involved in the following processes as physical or chemical changes:

1. Photosynthesis
2. Dissolving sugar in water
3. Burning of coal
4. Melting of wax
5. Beating aluminium to make aluminium foil
6. Digestion of food

Answer:

1. Chemical change
2. Physical change
3. Chemical change
4. Physical change
5. Physical change
6. Chemical change

Question 2.
State whether the following statements are true or false. In case a statement is false, write the correct statement in your notebook:
(a) Cutting a log of wood into pieces is a chemical change. (True/False)
(b) Formation of manure from leaves is a physical change. (True/False)
(c) Iron pipes coaled with zinc do not get rusted easily. (True/False)
(d) Iron and rust are the same substances. (True/False)
(e) Condensation of steam is not a chemical change. (True/False)
Answer:
(a) False
Correct statement: Cutting a log of wood into pieces is a physical change, ft, False
(b) True
Correct statement: The formation of manure from leaves is a chemical change.
(c) True
(d) False
Correct statement: Iron and rust are two different substances.
(e) True

Question 3.
Fill in the blanks in the following statements:

1. When carbon dioxide is passed through lime water, it turns milky due to the formation of …….
2. The chemical name of baking soda is ………
3. Two methods by which rusting of iron can be prevented are ……. and ……….
4. Changes in which only ………. properties of a substance change are called physical changes.
5. Changes in which new substances are formed are called ……. changes.

Answer:

1. calcium carbonate
2. sodium hydrogen carbonate
3. painting or greasing, galvanization
4. physical
5. chemical

Question 4.
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
Answer:
It is a chemical change. Here, a new substance carbon dioxide gas is formed.

Question 5.
When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
Answer:
When candle bums, both physical and chemical changes occur as given below:
(i) Physical change: Melting of wax, vapourisation of melted wax.
(ii) Chemical change: Burning of the vapours of wax to give carbon dioxide, heat, and light.
The burning of LPG in our kitchen is another such example in which a physical change occurs when LPG comes out of the cylinder and is converted to hum a liquid state to a gaseous state and a chemical change occurs when this gas burns in air.

Question 6.
How would you show that the setting of curd is a chemical change?
Answer:
When some sour substance is added to milk or kept overnight, it turns into curd. The curd in no way can be converted into milk i.e. irreversible change. Curd is a different substance than milk. So, the formation of curd is a chemical change.

Question 7.
Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
Answer:
Burning of wood is a chemical change because in burning new substances are formed as given below:
Wood + Oxygen → Coal + Carbon dioxide + Heat + Light.
While cutting it into small pieces is physical change because by cutting we can only reduce the size of the log of wood and no change in its chemical properties occurs and no new substance is formed.

Question 8.
Describe how crystals of copper sulphate are prepared.
Answer:
A cup of water is taken in a beaker and a few drops of dilute sulphuric acid are added into it. The water is heated. When it starts boiling, copper sulphate powder is added slowly while stirring continuously. Copper sulphate powder is added continuously till no more powder can be dissolved. The solution is filtered and allowed to cool down. Crystals of copper sulphate slowly form at the bottom of the beaker.

Fig. Crystals of copper sulphate

Question 9.
Explain how the painting of an iron gate prevents it from rusting.
Answer:
We know that the process of rusting requires exposure to both oxygen and water (or moisture). Painting prevents the surface of the iron gate from coming in contact with oxygen and moisture thus prevents it from rusting.

Question 10.
Explain why rusting of iron objects is faster in coastal areas than in deserts.
Answer:
In coastal areas, there is more moisture in the air due to the presence of the sea. But in the desert, there is a scarcity of water and hence the air is almost dry there. Both air and moisture are necessary conditions for rusting. So, rusting is faster in coastal areas than in deserts.

Question 11.
The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder, it exists as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change.
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(ii) Process – B is a chemical change.

Question 12.
Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change.
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(iii) Both processes A and B are chemical changes.

We hope the NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes help you. If you have any query regarding NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 9
Chapter Name	Reproduction in Animals
Number of Questions Solved	10
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals

NCERT TEXTBOOK EXERCISES

Question 1.
Explain the importance of reproduction in organisms.
Answer.
The production of new individuals from their parents is known as reproduction. Reproduction is very important as it ensures the continuation of a species. If the process of reproduction does not exist, the species would get vanished from the earth.

Question 2.
Describe the process of fertilisation in human beings.
Answer.
The first step in the process of reproduction is the fusion of a sperm and an ovum. Millions of sperms from the male are transferred into the female body. The sperms swim in the oviduct with the help of their tails to reach the egg. When they come in contact with the egg, one of the sperms may fuse with the egg.

Such fusion of the egg and the sperm is called fertilization. During fertilization, the nucleus of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote.

Question 3.
Choose the most appropriate answer:
(a) Internal fertilisation occurs
(i) in female body.
(ii) outside the female body.
(iii) in male body.
(iv) outside male body.
Answer.
(i) in female body.

(b) A tadpole develops into an adult frog by the process of
(i) fertilisation.
(ii) metamorphosis.
(iii) embedding.
(iv) budding.
Answer.
(ii) metamorphosis.

(c) The number of nuclei present in a zygote is
(i) none
(ii) one
(iii) two
(iv) four.
Answer.
(ii) one.

Question 4.
Indicate whether the following statements are True (T) or False (F):

1. Oviparous animals give birth to young ones. ( )
2. Each sperm is a single cell. ( )
3. External fertilisation takes place in frogs. ( )
4. A new human individual develops from a cell called gamete. ( )
5. Egg laid after fertilisation is made up of a single cell. ( )
6. Amoeba reproduces by budding. ( )
7. Fertilization is necessary even in asexual reproduction. ( )
8. Binary fission is a method of asexual reproduction. ( )
9. A zygote is formed as a result of fertilisation. ( )
10. An embryo is made up of a single cell. ( )

Answer.

1. False
2. True
3. True
4. False
5. True
6. False
7. False
8. True
9. True
10. False

Question 5.
Give two differences between a zygote and a foetus.
Answer.

Zygote	Foetus.
1.  It is single-celled.	1. It is multicellular.
2. Zygote is formed by the fusion of male and female gametes.	2. Foetus is formed by the repeated division of zygote and differentiation.

Question 6.
Define asexual reproduction. Describe two methods of asexual reproduction in animals. ‘
Answer.

The type of reproduction in which only a single parent is involved is called asexual reproduction.

Budding: The asexual reproduction in which an individual develops from buds, which is detached from a parent body is known as budding. For example, Hydra reproduces by this method. Many bulges are found in the parent body of hydra. These bulges called buds to develop into new individuals.

Budding fission: It is a type of asexual reproduction in which an animal reproduces by dividing into two individuals. This type of reproduction is observed in the microscopic organism, amoeba. The reproduction in Amoeba begins by a division of its nucleus into two nuclei. This is followed by a division of its body into two with each part receiving a nucleus. Finally, two amoebae are produced from a single Amoeba.

Question 7.
In which female reproductive organ does the embryo get embedded?
Answer.
The embryo gets embedded in the wall of the uterus (of the female) for further development.

Question 8
What is metamorphosis? Give examples.
Answer.
The drastic change that transforms a larva into an adult is called metamorphosis. Frog, SilkWorm, Honeybee, are some animals in which metamorphosis occurs.

Question 9.
Differentiate between internal fertilisation and external fertilisation.
Answer.

Fertilization	External fertilisation.
1.Takes place inside the body of the female.	1. Takes place outside the body of the female.
2. Female lays either fertilized eggs or a fully grown individual is born.	2. Female lays unfertilized eggs.

Question 10.
Across
1. The process of the fusion of the gametes.
6. The type of fertilisation in the hen.
7. The term used for bulges observed on the sides of the body of Hydra.
8. Eggs are produced here.
Down
2. Sperms are produced in these male reproductive organs.
3. Another term for in vitro fertilisation.
4. These animals lay eggs.
5. A type of fission in amoeba.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 9 Reproduction in Animals, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts.

Board	CBSE
Textbook	NCERT
Class	Class 7
Subject	Science
Chapter	Chapter 5
Chapter Name	Acids, Bases and Salts
Number of Questions Solved	11
Category	NCERT Solutions

NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts

Question 1.
State differences between acids and bases.
Answer:

Acids	Bases
1. Acids are sour to taste	1. Bases are bitter to taste.
2. Acids turn blue litmus red.	2. Bases turn red litmus blue.
3. Acid is defined as a substance which contains hydrogen ion.	3. A base is defined as a substance which contains hydroxyl ion.

 Question 2.
Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Answer:
Ammonia has basic nature.

Question 3.
Name the source from which litmus solution is obtained. What is the use of this solution?
Answer:
The extraction of litmus solution takes place from Lichens (a symbiotic association of algae and fungi). It is used to determine whether the given solution is acidic or basic.

Question 4.
Is the distilled water acidic, basic, or neutral? How would you verify it?
Answer:
Distilled water is neutral. We can verify it by showing that neither blue nor red litmus paper changes its colour when dipped in it.

Question 5.
Describe the process of neutralization with the help of an example.
Answer:
The process in which an acid reacts with a base to form salt and water is known as a neutralization reaction. For example,

Question 6.
Mark ‘T’ if the statement is true and ‘F’ if it is false :
(i) Nitric acid turns red litmus blue. (T/F)
(ii) Sodium hydroxide turns blue litmus red. (T/F)
(iii) Sodium hydroxide and hydrochloric acid neutralize each other and form salt and water. (T/F)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
(v) Tooth decay is caused by the presence of a base. (T/F)
Answer:
(i) F
(ii) F
(iii) T
(iv) T
(v) F

Question 7.
Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants a neutral drink. How will Dorji decide which drink is to be served to whom?
Answer:
He can decide by the use of an indicator. If the sample of drink turns red litmus blue, it is basic. If it turns blue litmus red, it is acidic. If it does not affect litmus, it is neutral.

Question 8.
Explain why :
(a) An antacid tablet is taken when you suffer from acidity.
(b) Calamine solution is applied on the skin when an ant bites.
(c) Factory waste is neutralised before disposing it into the water bodies.
Answer:
(a) To relieve indigestion, we take an antacid such as milk of magnesia. It neutralizes the effect of excessive acid.
(b) When an ant bites, it injects the acidic liquid into the skin. This acidic liquid is formic acid, which leads to inflammation to the skin. The effect of the sting can be neutralised by rubbing calamine solution which contains zinc carbonate. The zinc carbonate is a weak base and causes no harm to the skin.
(c) The wastes of many factories usually contain acids. If they are allowed to flow into the water bodies without neutralising it properly, then the acids will kill fish and other aquatic organisms. So factory wastes must be neutralised by adding some basic substances into the wastes before disposing these into water bodies.

Question 9.
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only a turmeric indicators.
Answer:

S.No.	Name of substance	Effect on turmeric indicator
1.	Hydrochloric acid	The yellow colour of turmeric turns blue
2.	Sodium hydroxide	The yellow colour of turmeric turns red
3.	Sugar solution	No change in turmeric colour

Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:
The solution may be neutral or basic. Both types of substances have no effect on blue litmus. Put a drop of this solution on a red litmus paper. If it turns blue, then the above solution is basic in nature and if no colour change occurs, then it is neutral.

Question 11.
Consider the following statements:
(a) Both acids and bases change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not give a change with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in acid, and a base depends on the type of the indicator.
Which of these statements are correct?
(i) All four
(ii) (a) and (d)
(iii) (b) and (c)
(iv) Only (d)
Answer:
(ii) (a) and (d)

We hope the NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts help you. If you have any query regarding NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 7 Science Chapter 4 Heat are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 4 Heat.

Board	CBSE
Textbook	NCERT
Class	Class 7
Subject	Science
Chapter	Chapter 4
Chapter Name	Heat
Number of Questions Solved	11
Category	NCERT Solutions

NCERT Solutions for Class 7 Science Chapter 4 Heat

Question 1.
State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer:
Similarities:

1. Both contain mercury in bulbs.
2. Both use the Celsius scale on a glass tube.

Differences:

1. The temperature on the laboratory thermometer falls by itself, but not so in the clinical thermometer.
2. The range of a laboratory thermometer is much higher than a clinical thermometer.

Question 2.
Give two examples each of conductors and insulators of heat.
Answer:

• Conductors of heat: Copper, iron.
• Insulators: Plastic, wood (dry).

Question 3.
Fill in the blanks:

1. The hotness of an object is determined by its …….
2. The temperature of boiling water cannot be measured by a ………. thermometer.
3. Temperature is measured in degree …………
4. No medium is required for transfer of heat by the process of ………..
5. A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ………
6. Clothes of ……….. colours absorb heat better than clothes of light colours.

Answer:

1. temperature
2. clinical
3. Celsius
4. radiation
5. conduction
6. dark

Question 4.
Match the following:

(i) Land breeze blows during	(a) summer
(ii) Sea breeze blows during	(b) winter
(iii) Dark-coloured clothes are preferred during	(c) day
(iv) Light-coloured clothes are preferred during	(d) night

Answer:

(i) Land breeze blows during	(d) night
(ii) Sea breeze blows during	(c) day
(iii) Dark-coloured clothes are preferred during	(b) winter
(iv) Light-coloured clothes are preferred during	(a) summer

Question 5.
Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Answer:
If there are more than one layer of clothes, air would be trapped in between them. Air is a poor conductor of heat. This increases the insulation and thus comfortability of the clothes as a whole.

Question 6.
Look at Fig., mark where the heat is being transferred by conduction, by convection, and by radiation.

Fig. Heat transferred by conduction, by convection and by radiation
Answer:
In this figure, the heat is transferred at three points in different ways:

• by radiation: from the flame to the bottom of the pan.
• by conduction: from lower surface to upper surface of the pan.
• by convection: from the base to the upper region of pan water.

Question 7.
In places of the hot climate, it is advised that the outer walls of houses be painted white. Explain.
Answer:
Objects with white surfaces reflect more heat and absorb less. So, less heat from outside would enter the house.

Question 8.
One liter of water at 30°C is mixed with one liter of water at 50°C. The temperature of the mixture will be
(a) 80°C
(b) more than 50°C but less than 80°C
(c) 20°C
(d) between 30°C and 50°C
Answer:
(d) between 30°C and 50°C.

Question 9.
An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will
(a) flow from the iron ball to water.
(b) not flow from iron ball to water or from water to iron ball.
(c) flow from water to iron ball.
(d) increase the temperature of both.
Answer:
(b) not flow from iron ball to water or from water to iron ball.

Question 10.
A wooden spoon is dipped in a cup of ice cream. Its other end
(a) becomes cold by the process of conduction.
(b) becomes cold by the process of convection.
(c) becomes cold by the process of radiation.
(d) does not become cold,
Answer:
(d) does not become cold.

Question 11.
Stainless steel pans are usually provided with copper bottoms. The reason for this could be that
(a) copper bottom makes the pan more durable.
(b) such pans appear colourful.
(c) copper is a better conductor of heat than stainless steel.
(d) copper is easier to clean than stainless steel.
Answer:
(c) copper is a better conductor of heat than stainless steel.

We hope the NCERT Solutions for Class 7 Science Chapter 4 Heat help you. If you have any query regarding NCERT Solutions for Class 7 Science Chapter 4 Heat, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 8
Chapter Name	Cell Structure and Functions
Number of Questions Solved	10
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions

NCERT TEXTBOOK EXERCISES

Question 1.
Indicate whether the following statements are True (T) or False (F):
(a) Unicellular organisms have a one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has an irregular shape. (T/F)
Answer.
(a) True
(b) True
(c) False
(d) True.

Question 2.
Make a sketch of the human nerve cell. What function do nerve cells
perform?
Answer.

The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.

Question 3.
Write short notes on the following:

1. Cytoplasm
2. Nucleus of a cell.

Answer.

1. It is the jelly-like substance found between the nucleus and the cell membrane. It contains the nucleus and many small structures called organelles. Cytoplasm, along with nucleoplasm, forms the living substance of the cell, called the protoplasm.
2. It is an important component of the living cell. It is generally spherical and located in the center of the cell. The Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. The liquid substance of the nucleus is termed nucleoplasm. There is a smaller spherical body in the nucleus which is called the nucleolus. The Nucleus also contains thread-like structures called chromosomes. These carry genes and help in inheritance. The Nucleus acts as the control center of the activities of the cell.

With a microscope of higher magnification, we can see a smaller spherical, dense body in the nucleus. It is called the nucleolus. In addition, the nucleus contains thread-like structures called chromosomes. These carry genes and help in the inheritance or transfer of characters from the parents to the next generation. The chromosomes can be seen only when the cell divides. The nucleus, in addition to its role in inheritance, acts as the control centre of the activities of the cell.

Question 4.
Which part of the cell contains organelles?
Answer.
The Cytoplasm contains organelles of the cell.

Question 5.
Make sketches of animal and plant cells. State three differences between them.
Answer.

Plant cells	Animal cells
1.  The outermost covering is cell wall which is made of cellulose. 2.   Plastids (e.g., chloroplasts) are present. 3.   Large vacuoles are present.	1. The outermost covering is the plasma membrane which is living material. 2.  Plastids are absent. 3.     No or small vacuoles Eire present.

Question 6.
State the difference between eukaryotes and prokaryotes.
Answer.

Eukaryotes	Prokaryotes
1. Nucleus of the cell has a nuclear membrane.	1. Nucleus is not bounded by a membrane.
2. Possess membrane-bound organelles.	2. Membrane-bound organelles are absent.
3. Examples include all higher plants and animals.	3. Examples are bacteria and blue-green algae.

Question 7.
Where are chromosomes found in a cell? State their functions.
Answer.
Chromosomes are found in the nucleus of the cell. They carry genes and help in inheritance i.e., transfer of characters from the parents to the offspring.

Question 8.
‘Cells are the basic structural units of living organisms. Explain.
Answer.
All organisms are made up of cells. They have different designs, shapes and sizes in the living organism. All the life processes take place inside a cell. Many similar cells aggregate together to make tissue. So many tissues are organised to form organs and finally, many organs are organised to form a system. So we can say that cells are the basic units of living organisms.

Question 9.
Explain why chloroplasts are found only in plant cells?
Answer.
Chloroplasts contain chlorophyll which synthesizes food in plants by the process of photosynthesis. As photosynthesis does not occur in animals, it does not contain chloroplasts.

Question 10.
Complete the crossword with the help of clues given below:
Across
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.
Down
1. Green plastids.
2. Formed by a collection of tissues.
4. It separates the contents of the cell from the surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 8 Cell Structure and Functions, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 7
Chapter Name	Conservation of Plants and Animals
Number of Questions Solved	11
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals

NCERT TEXTBOOK EXERCISES

Question 1.
Fill in the blanks:

1. A place where animals are protected in their natural habitat is called………….
2. Species found only in a particular area is known as…………
3. Migratory birds fly to faraway places because of…………… changes.

Answer.

1. wildlife sanctuary
2. endemic species
3. climatic.

Question 2.
Differentiate between the following:

1. Wildlife sanctuary and biosphere reserve
2. Zoo and wildlife sanctuary
3. Endangered and extinct species
4. Flora and fauna

Answer.

1. Wildlife Sanctuary: The area that is reserved in a forest for the protection and preservation of wild animals. It also provides suitable living conditions.
   Biosphere Reserve: The area that is meant for the conservation of biodiversity. It also helps to maintain the culture of that area. One biosphere reserve may also contain other protected areas in it.
2. Zoo: A place where animals are protected in an artificial habitat.
   Wildlife Sanctuary: The area, that is reserved in a forest for the protection and preservation of wild animals.
3. Endangered Species: The animal species whose numbers are diminishing to a level that they might face extinction.
   Extinct Species: The animal species, whose numbers are nil (zero), because of changes in their habitat and other calamities.
4. Flora: The plants that are found in a particular area are called flora. For example, Sal, teak, jamun etc.
   Fauna: The animals that are found in a particular area are called fauna. For example, Chinkara, cheeta, leopard etc.

Question 3.
Discuss the effects of deforestation on the following:

1. Wild animals
2. Environment
3. Villages (Rural areas)
4. Cities (Urban areas)
5. Earth
6. The next generation

Answer.

1. They won’t get their natural habitat and surroundings, as well as food. So either they will extinct or reach the verge of extinction or they will migrate to another forest. In course of their migration, they might be killed by humans.
2. Climatic changes disturb the environment. Global warming is caused due to accumulation of carbon dioxide. Because of deforestation and an increase in the temperature on earth, the water cycle will get disturbed and the reduced rainfall will cause droughts.
3. Villagers cannot grow food (crops) because of no rain as drought situations will prevail. Many poor villagers may die for want of food. The villagers will move to towns and cities. On one hand, villages will be completely deserted and on the other hand, the towns and cities will be overcrowded.
4. Cities flooded with drought-affected villagers will disturb the environment. Food-grains will either not available or if available, they will be costlier. People will also not get wood for making furniture and buildings.
5. Deforestation is a major cause, which leads to change in soil properties. Gradually the land will get converted into a desert. On the other hand, the snow of the mountains will melt due to global warming, and many coastal cities will be flooded causing disaster.
6. The next generation will either be extinct or if at all it exists, it will suffer from diseases and face life scarcity of food in life. So, the next generation will be ill, weak, and, consequently, face extinction.

Question 4.
What will happen if:

1. we go on cutting trees.
2. the habitat of an animal is disturbed.
3. the top layer of soil is exposed.

Answer.

1. If we go on cutting trees, then:
   • The survival of mankind will become a threat, because of the low oxygen concentration in the atmosphere.
   • We have to face high temperatures and increased pollution levels.
   • Natural calamities will disrupt our life.
   • The water cycle will be disturbed.
2. If the habitat of an animal is disturbed, then:
   • The animals will lose their natural habitat and ultimately will be at the periphery to become endangered.
   • The survival of animal will be difficult, because of the drought and the rise in temperature.
3. If the top layer of soil is exposed, then:
   • The exposed top layer loses all its nutrients, especially the hummus.
   • It leads to a decrease in the water holding capacity of the soil.
   • The vegetation will go off from the field, and desertification will be the result.

Question 5.
Answer in brief.

1. Why should we conserve biodiversity?
2. Protected forests are also not completely safe for wild animals. Why?
3. Some tribals depend on the jungle. How?
4. What are the causes and consequences of deforestation?
5. What is Red Data Book?
6. What do you understand by the term migration?

Answer.

1. Biodiversity refers to the variety in life existing on Earth, their interrelationships, and their relationship with the environment, so we should conserve as the food chain should not get disturbed, otherwise the whole ecosystem will be affected.
2. Protected forests are also not completely safe for wild animals, because poaching or capturing of the animal takes place in these areas. Wild animals are killed by poachers.
3. Tribes, usually the residents of the jungle, are dependent on the jungle for the fulfillment of their daily needs of life.
4. The causes and consequences of deforestation are:
   • It increases the temperature and pollution level on earth.
   • It decreases the level of oxygen in the atmosphere and groundwater level is also lowered.
   • The rainfall and the fertility of the soil will decrease.
   • The chances of natural calamities are more because of deforestation.
   • It changes the soil properties.
   • It affects the top layer of the soil, which exposes the lower hard and rocky layers.
5. The Red Data Book is the only source as a book, which keeps a record of all the endangered animals and plants.
6. The term migration means the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for some specific purposes like breeding or to overcome unfavourable conditions.

Question 6.
In order to meet the ever-increasing demand in factories and for shelter, trees are being continually cut. Is it justified to cut trees for such projects? Discuss and prepare a brief report.
Answer.
Of course, to meet the ever-increasing demand in factories and for shelter, trees are being continually cut, which is hot justified at all. If one tree is cut, at least five trees should be grown so that the reforestation process may remain continuous.

But, if trees are cut blindly and no trees are planted then the earth may face global warming, no rainfall, climatic change, soil erosion, and desertification, etc. So, cutting trees for any reason at all is not justified.

Question 7.
How can you contribute to the maintenance of the green wealth of your locality? Make a list of actions to be taken by you.
Answer.
For the contribution to maintain of green wealth in my locality, the different actions to be taken are:

1. not to allow anybody to cut any trees;
2. always try to plant saplings in the residing area;
3. never ever show the neglection to water the plants;
4. always trimming the plants from time to time for their better growth.

Question 8.
Explain how deforestation leads to reduced rainfall.
Answer.
Deforestation leads to the accumulation of CO₂ in the atmosphere which results in global warming as CO₂ traps the heat of the sunrays. The increase in temperature on earth will disturb the water cycle and reduce rainfall, causing drought in the region.

Question 9.
Find out about national parks in your state. Identify and show their location on the outline map of India.
Answer.
Do yourself.

Question 10.
Why should the paper be saved? Prepare a list of ways by which you can save paper.
Answer.
Manufacturing paper needs trees. By cutting trees, deforestation is caused which disturbs the balance in nature. If the paper is saved or recycled, many trees can be saved. Paper can be saved by recycling. Paper can be recycled.5-7 times and can be used. If everyone who uses paper, could save at least one sheet of paper in a day, we can save many trees in a year.

We should save and reuse the used paper and recycle it. By following these steps we can save not only the trees but also the energy and water needed for manufacturing paper.

Question 11.
Complete the word puzzle:
Down
1. Species on the verge of extinction.
2. A book carrying information about endangered species.
5. Consequence of deforestation.
Across
1. Species which have vanished.
3. Species found only in a particular habitat.
4. Variety of plants, animals, and microorganisms found in an area.
Answer.

We hope the NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 7 Conservation of Plants and Animals, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric.

Board	CBSE
Textbook	NCERT
Class	Class 7
Subject	Science
Chapter	Chapter 3
Chapter Name	Fibre to Fabric
Number of Questions Solved	9
Category	NCERT Solutions

NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric

Question 1.
You must be familiar with the following nursery rhymes:
(i) ‘Baa baa black sheep, have you any wool.
(ii) ‘Mary had a little lamb, whose fleece was white as snow.
Answer the following:
(a) Which parts of the black sheep have wool?
(b) What is meant by the white fleece of the lamb?
Answer:
(a) The hairy skin – called fleece, has wool in black sheep.
(b) White fleece means hairy skin which is white in colour.

Question 2.
The silkworm is (a) a caterpillar, (b) a larva. Choose the correct option.
(i) (a)
(ii) (b)
(iii) both (a) and (b)
(iv) neither (a) nor (b)
Answer:
(iii) both (a) and (b)

Question 3.
Which of the following does not yield wool?
(i) Yak
(ii) Camel
(iii) Goat
(iv) Woolly dog
Answer:
(iv) Woolly dog

Question 4.
What is meant by the following terms?

1. Rearing
2. Shearing
3. Sericulture

Answer:

1. Rearing: Bringing up and looking after the sheep is called rearing.
2. Shearing: To obtain wool, the fleece of the sheep along with a thin layer of skin is removed from its body. This process is called shearing.
3. Sericulture: The rearing of silkworms for obtaining silk is called sericulture.

Question 5.
Given below is a sequence of steps in the processing of wool. Which are the missing steps? Add them.
Shearing, ……., sorting ………, ………., ……….
Answer:
Shearing, scouring, sorting, picking out burrs, colouring, rolling.

Question 6.
Make sketches of the two stages in the life history of the silk moth which are directly related to the production of silk.
Answer:

Question 7.
Out of the following, which are the two terms related to silk production?
Sericulture, floriculture, moriculture, apiculture and silviculture.
Hints:
(i) Silk production involves the cultivation of mulberry leaves and rearing silkworms.
(ii) Scientific name of mulberry is Morus alba.
Answer:
Sericulture, Moriculture.

Question 8.
Match the words of Column I with those given in Column II:

Column I	Column II
1. Scouring	(a) Yields silk fibres
2. Mulberry leaves	(b) Wool yielding animal
3. Yak	(c) Food of silkworm
4. Cocoon	(d) Reeling
	(e) Cleaning sheared skin

Answer:

Column I	Column II
1. Scouring	(e) Cleaning sheared skin
2. Mulberry leaves	(c) Food of silkworm
3. Yak	(b) Wool yielding animal
4. Cocoon	(a) Yields silk fibres

Question 9.
Given below is a crossword puzzle based on this lesson. Use hints to fill in the blank spaces with letters that complete the words.

Down
(D) 1 : Thorough washing
2 : Animal fibre
3 : Long thread like structure
Across
(A) 1 : Keeps warm
2 : Its leaves are eaten by silkworms
3 : Hatches from egg of moth
Answer:

We hope the NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric help you. If you have any query regarding NCERT Solutions for Class 7 Science Chapter 3 Fibre to Fabric, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 6
Chapter Name	Combustion and Flame
Number of Questions Solved	13
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame

NCERT TEXTBOOK EXERCISES

Question 1.
List conditions under which combustion can take place.
Answer.
Conditions under which combustion can take place are as follows :

1. The presence of air (oxygen).
2. The ignition temperature should be reached.
3. A source of inflammable substance.

Question 2.
Fill in the blanks:

1. Burning of wood and coal causes………….of air.
2. A liquid fuel, used in homes is…………..
3. Fuel must be heated to its………… before it starts burning.
4. Fire produced by oil cannot be controlled by……………..

Answer.

1. pollution
2. Kerosene
3. ignition temperature
4. water.

Question 3.
Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer.
CNG is a clean fuel. It produces harmful products in a very small amount. That is why pollution in our cities has reduced.

Question 4.
Compare LPG and wood as fuels.
Answer.

LPG	Wood
1. No residue after burning.	1. Leaves a lot of ash on burning.
2. It can be easily stored in cylinders for convenient transportation.	2. Cannot be transported easily like LPG.
3. Burns easily.	3. Catches fire with more difficulty.
4. Low ignition temperature.	4. High ignition temperature.
5. No smoke on burning.	5. Burns with smoke.

Question 5.
Give reasons:

1. Water is not used to control fires involving electrical equipment.
2. LPG is a better domestic fuel than wood.
3. Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Answer.

1. Water is not used to control fires produced by .electrical equipment because water is a conductor of electricity and may cause electrocution or electric shock.
2. LPG is a substance which is readily available. It is cheaper and bums easily in the air at a moderate rate. It produces a large amount of heat and does not leave behind any undesirable substance.
3. Paper catches fire easily, but when it is wrapped around an aluminium pipe and heat is supplied then in the presence of aluminium pipe, the ignition temperature of the paper does not reach, because heat given to it is passed to the aluminium pipe which lowers the temperature of the paper. That is why the paper does not catch fire.

Question 6.
Make a labelled diagram of a candle flame.
Answer.

Fig. 6.1. Different zones of a candle flame

Question 7.
Name the unit in which the calorific value of a fuel is expressed.
Answer.
The calorific value of a fuel is expressed in kilojoules per kg (kJ/kg).

Question 8.
Explain how CO₂ is able to control fires.
Answer.
CO₂, being heavier than oxygen, covers the fire like blanket and also brings down the temperature of fuel. Since the contact between the fuel and oxygen is cut off, the fire comes under control.

Question 9.
It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer.
Green leaves contain a lot of water. So, when we try to burn green leaves, water present in the leaves cools the combustible materials (leaves), so that their temperature is brought below their ignition temperature. This prevents the burning of green leaves.

On the other hand, dry leaves do not contain any water. So when a burning process starts, their temperature is raised drastically above their ignition temperature and the leaves catch fire easily.

Question 10.
Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer.
A goldsmith uses the outermost zone of a flame for melting gold and silver because it is the hottest zone of the flame (temperature ≈ 800°C) and is non-luminous in nature.

Question 11.
In an experiment, 4.5 kg of fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.
Answer.
The calorific value of the fuel:
Calorific value = heat produced/amount of fuel = 1,80,000 kJ/4.5 kg = 40,000 kJ/kg

Question 12.
Can the process of rusting be called combustion? Discuss.
Answer.
Yes, the process of rusting can be called combustion, in fact, slow combustion because rusting also takes place in the air (O₂) in the presence of humidity.

Question 13.
Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Answer.
The water of Ramesh’s beaker will get heated in a shorter time because the outermost part of the flame is the hottest.

We hope the NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame, drop a comment below and we will get back to you at the earliest

NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 18
Chapter Name	Pollution of Air and Water
Number of Questions Solved	11
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water

NCERT TEXTBOOK EXERCISES

Question 1.
What are the different ways in which water gets contaminated?
Answer.
Water gets contaminated due to the addition of substances harmful to health. Sewage, agricultural chemicals, and industrial waste are some of the major contaminants of water.

Question 2.
At an individual level, how can you help to reduce air pollution?
Answer.
At the individual level we can do the following things to reduce air pollution:

1. Use CNG and unleaded petrol instead of ordinary petrol and diesel.
2. Use public transport as far as possible.
3. Generate awareness about air pollution among the members of our family and friends.
4. We can plant trees and nurture the ones already present in the neighborhood.

Question 3.
Clear, transparent water is always fit for drinking. Comment.
Answer.
No, water which looks clean may still have disease-carrying microorganisms and dissolved impurities. Hence, it is not always fit for drinking, so it is essential to purify water before drinking, say for example by boiling process.

Question 4.
You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.
Answer.
Following are some of the measures that would help our town to ensure the supply of clear water to all its residents:

1. Make the supply system leakproof as a lot of drinking water is being wasted through the leakages.
2. Proper cleaning of the water tank from time to time.
3. Chlorine tablets should be made available.
4. The water supply pipes should not come in contact with the sewage pipes.

Question 5.
Explain the differences between pure air and polluted air.
Answer.
Pure air is free from any pollutant, has no smell, is soothing, and not irritating to the eyes. Whereas polluted air gives a filthy smell and people cannot breathe in ut. If people inhale such (impure or polluted) air, they may suffer from various breathing, heart, and lung problems. Even sometimes people die inhaling polluted air.

Question 6.
Explain circumstances leading to acid rain. How does acid rain affect us?
Answer.
Pollutants like sulphur dioxide and nitrogen dioxide react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. These come down with the rain, making the rain acidic. This is called acid rain.
Acid rain affects us in many ways, e.g.

1. Acid rain removes basic nutrients such as calcium from the soil.
2. Acid rain increases the corrosion of metals.
3. Acid rain damages buildings and sculptural materials.
4. The low pH of add rainwater changes the rate of metabolism of some organisms.
5. Add rain causes damage to freshwater life, e.g., decrease in fish population of lakes.
6. Add mists cause direct damage to the leaves of plants.

Question 7.
Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen
Answer.
(d) Nitrogen

Question 8.
Describe the ‘Green House Effect’ in your own words.
Answer.
The sun’s rays when fall on the earth’s surface, warm it. Some of the sun’s rays are absorbed by the earth’s surface and left out rays are reflected back into space. Some of these rays are trapped by gases like C0₂, methane, etc. in the atmosphere, and these are not allowed to go out of the earth’s atmosphere.

These trapped rays begin to warm the earth’s surface. This causes heating of the earth’s atmosphere. This effect is named the Greenhouse effect because this is exactly like the greenhouse effect in a nursery.

Question 9.
Prepare a brief speech on global warming. You have to deliver the speech in your class.
Answer.
Today, global warming has appeared as one of the most severe threats to humankind. On one hand, carbon dioxide is added to the atmosphere due to human activities, by the other, as forest areas are also decreasing.

Question 10.
Describe the threat to the beauty of the Taj Mahal.
Answer.
Over the past 2 decades, India’s most famous tourist attraction, the Taj Mahal located at Agra, has become a matter of great concern. Experts have warned that air pollution is discolouring its white marble. So it is not only living organisms that get affected by polluted air but also the non-living things like buildings, monuments, and statues that are going to be affected.

The industries located in and around Agra like rubber processing, automobiles, chemicals and especially, the Mathura Oil Refinery have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. These come down with the rain, making the rain acidic. This is called acid rain. Acid rain has resulted in corrosion of the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particle emitted by the Mathura oil refinery, has contributed to the yellowing of the marble.

The Supreme Court has taken several steps to save the Taj Mahal. It has issued orders for the industries to either switch to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas) or to move to faraway places. Moreover, the automobiles should switch over to unleaded petrol in the Taj Mahal Zone.

Question 11.
Why does the increased level of nutrients in the water affect the survival of aquatic organisms?
Answer.
Chemicals used as fertilizers in agriculture dissolve in water and are washed away into water bodies from the field. The excessive quantities of chemicals like nitrates and phosphates which are present in fertilisers act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. They use up a lot of oxygen. This results in a decrease in the oxygen level which is harmful to the survival of other organisms.

We hope the NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 18 Pollution of Air and Water, drop a comment below and we will get back to you at the earliest.

NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum are part of NCERT Solutions for Class 8 Science. Here we have given NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum.

Board	CBSE
Textbook	NCERT
Class	Class 8
Subject	Science
Chapter	Chapter 5
Chapter Name	Coal and Petroleum
Number of Questions Solved	9
Category	NCERT Solutions

NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum

NCERT TEXTBOOK EXERCISES

Question 1.
What are the advantages of using CNG and LPG as fuels?
Answer.
The advantages of using CNG and LPG as fuels are as follows:

1. These are clean fuels.
2. These are low-cost fuels.
3. These are available easily.
4. These can be used directly for burning in homes and factories where it can be supplied through pipes.

Question 2.
Name the petroleum product used for surfacing roads.
Answer.
A petroleum product ‘Bitumen’ is used for surfacing of roads.

Question 3.
Describe how coal is formed from dead vegetation. What is this process called?
Answer.
About 300 million years ago, the earth was having dense forests in low-lying wetland areas. Due to earthquakes and volcanic eruptions, these forests got buried under the soil. As more soil deposited over them, they were compressed.

The temperature also raised as they sank deeper and deeper. Due to high temperature and lack of oxygen, dead plants inside the earth got slowly converted to coal. As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonization.

Question 4.
Fill in the blanks:
(a) Fossil fuels are.…….,…………. and………..
(b) Process of separation of different constituents from petroleum is called………………
(c) Least polluting fuel for a vehicle is……………
Answer.
(a) coal, petroleum, natural gas
(b) refining
(c) CNG.

Question 5.
Tick True/False against the following statements:
(a) Fossil fuels can be made in the laboratory.   (T/F)
(b) CNG is more polluting fuel than petrol.   (T/F)
(c) Coke is almost pure form of carbon.  (T/F)
(d) Coal tar is a mixture of various substances.   (T/F)
(e) Kerosene is not a fossil fuel.  (T/F)
Answer.
(a) False
(b) False
(c) True
(d) True
(e) False.

Question 6.
Explain why fossil fuels are exhaustible natural resources.
Answer.
Fossil fuels are present in nature in limited quantity and are being exhausted abundantly by us. That is why fossil fuels are called exhaustible natural resources.

Question 7.
Describe characteristics and uses of coke.
Answer.
Coke is a tough, porous, and black substance. It is an almost a pure form of carbon. “Coke is obtained by heating soft coal in the absence or little supply of air”.
It is used in the manufacture of steel and in the extraction of many metals.

Question 8.
Explain the process of the formation of petroleum.
Answer.
Petroleum is formed from organisms living in the sea. When these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, they were transformed into petroleum and natural gas under the absence of air and the presence of high temperature and pressure.

Question 9.
The following table shows the total power shortage in India from 1991-1997.
Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis.
Answer.

S. No.	Year	Shortage (%)
1	1991	7.9
2	1992	7.8
3	1993	8.3
4	1994	7.4
5	1995	7.1
6	1996	9.2
7	1997	11.5

We hope the NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum help you. If you have any query regarding NCERT Solutions for Class 8 Science Chapter 5 Coal and Petroleum, drop a comment below and we will get back to you at the earliest