Prasanna

On this page, you will find Direct and Indirect Proportions Class 8 Notes Maths Chapter 13 Pdf free download. CBSE NCERT Class 8 Maths Notes Chapter 13 Direct and Indirect Proportions will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Maths Chapter 13 Notes Direct and Indirect Proportions

Direct and Indirect Proportions Class 8 Notes Conceptual Facts

1. The two quantities are said to be directly proportional if

• an increase in one leads to a corresponding increase in the other.
• a decrease in one leads to a corresponding decrease in the other.

2. If x varies directly as y then the ratio \(\frac{x}{y}=k\) (constant) symbolically, x α y, where α is symbol of
proportionality or x = ky \(\frac{x_{1}}{y_{1}}=\frac{x_{2}}{y_{2}}=\frac{x_{3}}{y_{3}}=k\)

3. The two quantities are said to be inversely proportional if

• an increase in one leads to a corresponding decrease in the other.
• a decrease in one leads to a corresponding increase in the other.

4. If x varies inversely with y, then x α \(\frac{1}{y}\) ⇒ xy = k(constant) or xy – x₁y₁ = x₂y₂ = k.

5. Speed =\(\frac{\text { Distance }}{\text { Time }} \) or Distance = Speed x time or time =\(\frac{\text { Distance }}{\text { Speed }}\)

On this page, you will find Exponents and Powers Class 8 Notes Maths Chapter 12 Pdf free download. CBSE NCERT Class 8 Maths Notes Chapter 12 Exponents and Powers will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Maths Chapter 12 Notes Exponents and Powers

Exponents and Powers Class 8 Notes Conceptual Facts

• A numeral (a)ⁿ is called an exponential expression where a is called base and n the exponent or power.
  aⁿ = a x a x a x a……… x a (n times)
• A negative rational number raised to an even power is always positive, \(\text { e.g. },\left(-\frac{1}{2}\right)^{4}=\frac{1}{16}\)
• A negative rational number raised to an odd power is always negative, i.e., \(=\left(-\frac{1}{2}\right)^{3}=-\frac{1}{8}\)

Laws of exponents:

On this page, you will find Cell Structure and Function Class 8 Notes Science Chapter 8 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 8 Cell Structure and Function will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 8 Cell Structure and Function

Cell Structure and Function Class 8 Notes Understanding the Lesson

1. The basic structural and functional units of all the organs of the living organisms is called cell.

2. Cells were first discovered by Robert Hooke in 1665.

3. Cells of living organisms could be observed only after the discovery of improved microscopes.

4. Cells exhibit a variety of shapes and sizes.

5. Number of cells also varies from organism to organism.

6. Organisms made of more than one cell are called multicellular organisms while organisms made up of single cell are called unicellular organisms.

7. A single-celled organism, e.g., Amoeba captures and digests food, respires, excretes, grows and reproduces. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues.

8. A white blood cell (WBC) in human blood is an example of a single cell which can change its shape.

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

10. The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest cell measuring 170 mm x 130 mm, is the egg of an ostrich.

11. Each organ is further made up of smaller parts called tissues.

12. A tissue is a group of similar cells performing a specific function.

13. The basic components of a cell are cell membrane, cytoplasm and nucleus.

14. Cell membrane is also called plasma membrane or cytoplasmic membrane. The cell membrane separates cells from one another and also the cell from the surrounding medium. It is porous and allows the movement of substances or materials both inward and outward.

15. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity to these cells.

16. The jelly-like substance between the nucleus and the cell membrane is called cytoplasm. Various components or organelles, like mitochondria, golgi bodies, ribosomes, etc., are present in cytoplasm.

17. The central dense round body in the centre is called the nucleus.

18. The membrane which separates nucleus from the cytoplasm is called the nuclear membrane.

19. Cells without well-organised nucleus, i.e., lacking nuclear membrane, are called prokaryotic cells.

20. The smaller spherical body in the nucleus is called the nucleolus.

21. Chromosomes are the thread-like structures which carry genes and help in inheritance or transfer of characters from the parents to the offspring.

22. Plant cell differs from animal cell in having a central large vacuole, cell wall and plastids.

23. The blank-looking structures in the cytoplasm are called vacuole.

24. Plastids are the coloured organelles, that are found in plant cells only.

25. Green coloured plastids are called chloroplasts.

Class 8 Science Chapter 8 Notes Important Terms

Cell: Cell is the basic structural and functional unit of all living organisms.

Cell membrane: The membrane around the cell is called cell membrane. It is also called plasma membrane or cytoplasmic membrane.

Cell wall: The hard and rigid covering of plasma membrane which are found in plant cells only is called cell wall.

Chloroplasts: The green coloured plastids having chlorophyll, which is essential for photosynthesis is called chloroplasts.

Chromosomes: The thread like structures found in the nucleus which carry genes are called chromosomes.

Eukaryotes: Organisms which have eukaryotic cells, i.e., which contains a well developed nucleus are called eukaryotes.

Gene: Genes are located in chromosomes. It is a unit of inheritance in living organisms.

Multicellular: The category of organism like plants and animals which contains a large number of cells are called multicellular organisms.

Nuclear membrane: Nuclear membrane separates nucleus from cytoplasm.

Nucleolus: The smaller, spherical and dense body inside the nucleus is called nucleolus.

Nucleus: The denser region of the cell that may be present at the centre of the cell is called nucleus.

Organ: The group of tissues, which are specialised to perform specific functions is called organ.

Organelle: One of the smaller component of cell is known as organelle.

Plasma membrane: The other name of cell membrane is plasma membrane. It is a membrane around the cell.

Plastids: The coloured organelles, that are found in plant cells only are called plastids.

Prokaryotes: The organisms which have prokaryotic cells, i.e., lack true nucleus are called prokaryotes, e.g., bacteria and blue green algae.

Protoplasm: The viscous fluid inside the cell which provides living nature to it is called protoplasm.

Pseudopodia: The temporary projections protruding out of the body of Amoeba for locomotion and taking food. These appear and disappear as Amoeba moves.

Tissue: A group of similar cells performing a specific function is called tissue.

Unicellular: The category of organisms containing single cell are called unicellular organisms.

Vacuoles: Vacuoles are the empty or blank looking structures in the cytoplasm.

White Blood Cell (WBC): It is the component of blood cells. It is an example of a single cell which can change its shape.

On this page, you will find Conservation of Plants and Animals Class 8 Notes Science Chapter 7 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 7 Conservation of Plants and Animals will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 7 Conservation of Plants and Animals

Conservation of Plants and Animals Class 8 Notes Understanding the Lesson

1. There are a number of plants and animals that exist on earth.

2. Deforestation means cutting down of forests.

3. The chances of natural calamities like droughts and floods increase due to the deforestation.

4. An ecosystem is made of all the plants, animals and microorganisms in an area along with non-living components such as climate, soil, river, deltas, etc.

5. Plants and animals of a particular area are known as flora and fauna, respectively, of that area.

6. The conversion of fertile lands into deserts is known as desertification.

7. To protect our flora and fauna and their habitats, protected areas called sanctuaries, national parks and biosphere reserves have been earmarked. Activities like plantation, cultivation, grazing, felling trees, hunting and poaching are prohibited there.

8. Biosphere reserves are large areas of protected land for conservation of wildlife, plant and animal resources and traditional life of the tribals living in that area.

9. A sanctuary is an area where animals are kept protected from the disturbances to them and their habitats.

10. National Parks are areas reserved for wildlife where they can freely use the habitats and natural resources.

11. Those species of plants and animals which are found exclusively in a particular area are termed as ‘endemic species’.

12. Species is a group of population which are capable of interbreeding.

13. Project Tiger was launched by the government to protect tigers in the country.

14. Extinct species are those which have disappeared completely from the earth. Example, Dodo and passenger pigeon.

15. Critically endangered species are those which are under highest risk of extinction as their number has decreased drastically. Example, Andean catfish, Abe’s salamander.

16. Endangered animals are those whose numbers are diminishing to such a level that they might face I extinction. Example, great Indian bustard and blue whale.

17. Vulnerable species are those which are most likely to become endangered if not taken care of.

18. Near threatened species are found in small numbers and are scattered all over the world.

19. A sourcebook that keeps a record of all the endangered plants and animals is called ‘Red Data Book’.

20. Migration is the phenomenon of movement of a species from its own habitat to some other habitat for a particular time period every year for a specific purpose like breeding.

21. Reforestation is restocking of the destroyed forests by planting new trees.

Class 8 Science Chapter 7 Notes Important Terms

Biodiversity: It is the variety of different types of plant and animal life in a particular habitat (or in the world as a whole).

Biosphere reserve: A large; protected area of land meant for conserving wildlife, biodiversity, and the traditional lifestyle of the tribal people living in the area is known as a ‘biosphere reserve’.

Deforestation: The cutting down of trees on a large scale is called deforestation.

Desertification: The conversion of fertile lands into deserts is called desertification.

Ecosystem: It is a system formed by the interaction of a community of organisms with their physical environment.

Endangered species: Those species whose numbers are so small that the species are at risk of extinction are called endangered species.

Endemic species: They are the species of plants and animals which are found exclusively in a place.

Extinct animals: Animals which no more exist anywhere on the earth are known as extinct animals.

Fauna: The animals of a particular area are known as fauna of that area.

Flora: They are the plants of a particular area.

Migratory birds: Birds which move from one place to another for some reasons like breeding, climatic changes, etc., are known as migratory birds.

National park: The areas reserved for wildlife where they can freely use the habitats and natural resources are known as national parks.

Red Data Book: A source book that keeps a record of all the endangered animals, plants and other species.

Reforestation: The replanting or restoration of a forest that had been reduced by fire or cutting is called reforestation.

Sanctuary: The area where animals are kept protected from any disturbance to them or their habitat is known as a sanctuary.

On this page, you will find Combustion and Flame Class 8 Notes Science Chapter 6 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 6 Combustion and Flame will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 6 Combustion and Flame

Combustion and Flame Class 8 Notes Understanding the Lesson

1. Combustion is a chemical process in which a substance reacts with oxygen to give out heat energy.

2. All the substances that undergo combustion are said to be combustible.

3. A combustible substance may be solid, liquid or gaseous.

4. The presence of air is very necessary for combustion.

5. The lowest temperature at which a substance catches fire is known as its ignition temperature.

6. Some substances have very low ignition temperatures and they catch fire easily with a flame. They are known as inflammable substances; e.g., Petrol, LPG (Liquefied Petroleum Gas), alcohol, etc.

7. There are three significant requirements for producing fire fuel, air (for the supply of oxygen), and heat (to raise the temperature of the fuel above its ignition temperature).

8. When a substance burns rapidly and produces heat and light, the combustion is called rapid combustion.

9. When a material begins to burn suddenly without any external supply of heat or friction, the combustion is called spontaneous combustion; e.g., white phosphorus catches fire even at 25°C.

10. So, when the temperature goes beyond 25°C in summer, it catches fire automatically.

11. During combustion, when a large amount of heat and light is released with a bang or force, along with the production of gas, the combustion is called an explosion; e.g., bombs and fireworks, etc.

12. Flame is the region where combustion of gaseous substances or vapour goes on.

13. There are three distinct zones of a flame dark zone, luminous zone and non- luminous zone.

14. The amount of heat energy produced on burning 1 kg of a fuel completely is called the calorific value of that fuel.

15. The calorific value of a fuel is expressed in a unit called kilojoule per kilogram (kJ/kg).

16. A good fuel is one which is readily available, cheap, burns easily, produces large amount of heat and does not leave any undesirable substances.

17. The cutting down of trees is termed as ‘deforestation’.

18. The rise in temperature of the atmosphere of the earth is called global warming.

19. Water is commonly used to extinguish fire.

20. Rain containing acids that form in the atmosphere when industrial gas emissions (especially sulphur dioxide and nitrogen oxides) combine with water is known as acid rain.

Class 8 Science Chapter 6 Notes Important Terms

Acid rain: Rain containing acids that form in the atmosphere when industrial gas emissions (especially sulphur dioxide and nitrogen oxides) combine with water is known as acid rain. It harms trees, crops and buildings.

Calorific value: The amount of heat energy produced on combustion of 1 kg of fuel completely is called its calorific value.

Combustion: It is a chemical process in which a substance reacts with oxygen (in air) to emit heat and light.

Deforestation: The removal of trees on a large scale is termed as deforestation.

Explosion: A combustion reaction during which a large amount of heat and light energy is released, along with a bang or force with the production of gas, is called explosion.

Flame: It is a region where the combustion of gaseous substances or vapour goes on.

Fire extinguisher: A manually operated device used for extinguishing fire is known as a fire extinguisher.

Fuel: It is a material which is burn to produce heat.

Fuel efficiency: It is a parameter used to check the quality of fuel. It is expressed in term of its calorific value.

Global warming: An increase in the average temperature of the earth’s atmosphere, especially a sus-tained increase that causes climatic changes.

Ideal fuel: It is the fuel, that satisfies all the necessities of a fuel for specific uses.

Ignition temperature: The lowest temperature at which a substance catches fire is called its ignition temperature.

Inflammable substances: They are the substances that have a very low ignition temperature, and that can easily burn with a flame.

On this page, you will find Coal and Petroleum Class 8 Notes Science Chapter 5 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 5 Coal and Petroleum will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 5 Coal and Petroleum

Coal and Petroleum Class 8 Notes Understanding the Lesson

1. All the things that are required to fulfil our needs are called resources.

2. Some resources like air, water, fuels, plants occur in nature. They are called natural resources.

3. Some resources like plastics, machines, etc., are man-made.

4. Natural resources are classified as:

• Inexhaustible natural resources and
• Exhaustible natural resources.

5. Inexhaustible natural resources are present in unlimited quantity in nature; e.g., sunlight, air, etc. Exhaustible natural resources are present in limited quantity in nature; e.g., petroleum, natural gas, wildlife, forest, etc.

6. Some of exhaustible resources are renewable while some are non-renewable.

7. Natural fuels that are made up by the dead remains of living organisms for over a long period of time, are called fossil fuels.

8. Fossil fuels may be divided into three categories:

• Solid – Coal
• Liquid – Petroleum
• Gas – Natural gas

9. Coal is black-coloured hard substance that mainly contains carbon.

10. Coal is one of the main sources of energy worldwide.

11. Coal is one of the fuels used to cook food, run engines, generate electricity and to run various industries. Millions of years ago, trees, plants, ferns and forests got buried below the rocks, soil and sand.

12. Under anaerobic condition high temperature and pressure, the carbon enriched organic matter of plants slowly got converted into coal.

13. This slow process of conversion of wood into coal is called carbonisation.

14. Destructive distillation of coal is done at 1000°C in absence of air to obtain many other useful organic and inorganic substances from it, such as coke, coal tar and coal gas.

15. Coke is a tough, porous and black substance. It is an almost pure form of carbon.

16. Coke is used in the manufacture of steel and in the extraction of many metals.

17. Coal tar is a black, thick liquid with an unpleasant smell. It is a mixture of about 200 substances.

18. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and industry like dyes, drugs, naphthalene balls, paints, plastics, etc.

19. Coal gas is produced during the processing of coal to get coke.

20. It is used as a fuel in many industries situated near the coal processing units.

21. The word ‘petroleum’ is derived from petra meaning ‘rock’ and oleum meaning ‘oil’.

22. Petroleum is a dark coloured viscous fluid and like all the other oils, it is lighter than water.

23. Petroleum was formed when organisms living in the sea are buried underneath sedimentary rock and subjected to intense heat and pressure under anaerobic condition.

24. Petroleum has such a great significance that it is named as ‘black gold’.

25. Separation of different constituents of petroleum through fractional distillation is called refining of petroleum.

26. Refining of petroleum is carried out in a petroleum refinery.

27. Natural gas is a very important fossil fuel because it is easy to transport through pipes.

28. Natural gas is stored under high pressure as compressed natural gas (CNG).

29. The great .advantage of CNG is that it can be used directly for burning in homes and factories.

30. We must use the fuels only when it is absolutely necessary.

31. In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/ diesel while driving.

32. To conclude, we can say that fossil fuels are our very important resources of energy. But as they are limited, we should use them judiciously.

Class 8 Science Chapter 5 Notes Important Terms

Coal: A fossil fuel, formed by the decay of vegetation which existed millions of years ago is called coal.

Coal gas: A mixture of gases produced during destructive distillation of coal is called coal gas.

Coal tar: Coal tar is a black coloured thick, viscous liquid which is obtained as byproduct when coal is carbonised to make coke.

Coke: On heating the coal strongly, the volatile impurities escape out from it and solid, pure carbon residue is left behind which is called coke.

Fossil fuel: Natural fuel that made up by burial of living organisms under deep down the earth for over a long period of time is called fossil fuel.

Natural gas: The gaseous mixture of lower hydrocarbon which occur deep inside the earth either alone or covering the crude oil in an oil field is called natural gas.

Petroleum: A dark coloured thick crude oil found deep below the ground is called petroleum.

Petroleum refinery: A place where process of separating the various constituents of petroleum is car-ried out is called petroleum refinery.

On this page, you will find Materials: Metals and Non-Metals Class 8 Notes Science Chapter 4 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 4 Materials: Metals and Non-Metals will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 4 Materials: Metals and Non-Metals

Materials: Metals and Non-Metals Class 8 Notes Understanding the Lesson

1. Materials can be broadly grouped into two groups metals and non-metals.

2. Substances which are generally hard, lustrous, malleable, sonorous and good conductors of heat and electricity are metals. For example, copper, iron, gold, silver, etc.

3. Substances which are generally soft, dull in appearance, brittle, non-sonorous and bad conductors of heat and electricity are non-metals. For example, oxygen, hydrogen, carbon, sulphur, etc.

4. The property of metals by which they can be beaten into thin sheets is called malleability.

5. The property of metal by which it can be drawn into wires is called ductility.

6. The property of metal of producing ringing sound is called sonority.

7. Chemical properties of metals and non-metals:

(i) Reaction with oxygen: Both metals and non-metals form their oxides when burnt in oxygen. Metals form basic oxides whereas non-metals generally form acidic oxides.
Reactions of metal or non-metal with oxygen are called oxidation reactions.

(ii) Reaction with water: Metals produce their oxides or hydroxides and hydrogen gas on reacting with water. Non-metals do not react with water.

(iii) Reaction with acids: Metals react with acids and produce metal salts and hydrogen gas. Hydrogen gas burns with a ‘pop’ sound, when a burning matchstick is brought near it.
Non-metals generally do not react with acids.

(iv) Reaction with bases: Most of the metals and non-metals generally do not react with bases. Some metals like aluminium, lead and zinc react with strong bases like sodium hydroxide to make complex salts and hydrogen gas. Similarly, sometimes some complex reactions take place between non-metals and bases.

(v) Displacement reactions: Reactions in which more reactive metal displaces the less reactive metal from its salt is called displacement reactions. Certain metals are capable of displacing other metals from their solutions. For example, zinc (Zn) replaces copper from copper sulphate solution. The reaction is as follows:

8. On the basis of reactivity of metals a sequence is formed called reactivity series. Metals on the top of the series are most reactive and those on the bottom are least reactive. Zinc is more reactive than copper and iron. A more reactive metal can replace a less reactive metal but, a less reactive metal cannot replace a more reactive metal.

9. Uses of metals: Metals are used in making machinery, automobiles, aeroplanes, trains, satellites, industrial gadgets, water boilers, utensils, etc. They are also used in making wires and sheets.

10. Uses of non-metals

• All living beings inhale oxygen during breathing, which is a non-metal.
• Non-metals like nitrogen, phosphorus and potassium are used in fertilisers to enhance the growth of plants.
• Non-metal like chlorine is used in water purification process.
• Non-metal is used in the purple coloured solution which is applied on wounds as an antiseptic.
• Non-metals are used in crackers.

Class 8 Science Chapter 4 Notes Important Terms

Atom: An atom is the smallest particle of an element which cannot be further divided by any physical mean.

Conductor: Substance which allow heat and electricity to pass through it is called conductor.

Displacement reaction: Reaction in which more reactive element displaces less reactive element is known as displacement reaction.

Ductility: The property of metals due to which they can be drawn into wires is called ductility. Metals are ductile.

Elements: The substances whose molecules are made up of only one type of atoms are known as elements.

Hardness: It is the property of a substance due to which it cannot be cut easily is called its hardness. Metals possess this property.

Malleability: It is the property of a substance due to which it can be beaten into thin sheets is called malleability. Metals have this property.

Metals: Substances which are generally shiny, hard, malleable, ductile, sonorous and good conductors of heat and electricity are metals.

Metalloid: Substances which possess properties of both metals and non-metals are called metalloids. For example, bismuth, antimony, arsenic and boron.

Non-metals: Materials which are soft, dull in appearance, non-sonorous and poor conductors of heat and electricity are called non-metals. They break down into a powdery mass on tapping with a hammer. They also form negative ions by gaining electrons.

Sonorous: The property due to which metals produce a ringing sound is called sonority. This is why metals are called to be sonorous.

On this page, you will find Synthetic Fibres and Plastics Class 8 Notes Science Chapter 3 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 3 Synthetic Fibres and Plastics will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 3 Synthetic Fibres and Plastics

Synthetic Fibres and Plastics Class 8 Notes Understanding the Lesson

1. A fabric is the material used for making clothes.

2. Fabrics are made from fibres obtained from natural or artificial source.

3. Beside clothes, fibres are also used for making carpets, sail of boats, parachutes, upholstery and many more items.

4. Fibres can be natural or artificial. Fibres such as cotton, wool, jute and silk are natural fibres whereas rayon, nylon and polyester are artificial fibres.

5. The man-made fibres produced from chemical substances are called synthetic fibres.

6. Synthetic fibres are also known as man-made fibres or artificial fibres.

7. Depending upon the types of chemicals used for manufacturing of the synthetic fibres they are called rayon, nylon, polyester and acrylic.

8. Rayon or artificial silk is made from cellulose obtained from wood pulp.

9. It can be dyed in a wide variety of colours.

10. Nylon was the first synthetic fibre produced by man in 1935.

11. Nylon fibres are strong, elastic, light, lustrous and easy to wash.

12. It is used to make many items like socks, ropes, tents, toothbrushes, car seat belts, curtains, etc.

13. Terylene and dacron are polyester fibres.

14. It is made from two monomers, terephthalic acid and ethylene glycol.

15. It is used for making PET bottles, jars, floppy discs, shirts, hats, etc.

16. Acrylic is the synthetic fibre that resembles wool in its texture and properties.

17. It is used to make sweaters, shawls, socks, etc.

18. They dry up soon, are durable, less expensive, readily available and easy to maintain.

19. A plastic is a synthetic material which can be set into desired shape when soft and then hardened to produce a durable article.

20. Some plastic polymers have linear arrangement of units, whereas in others it is cross-linked arrangement.

21. Thermoplastic is a plastic which gets deformed easily on heating and can be bent easily, e.g., polythene and PVC. These are used for manufacturing toys, combs, containers, etc.

22. Thermosetting plastics is a plastic which when moulded once cannot be softened by heating, e.g., bakelite and melamine.

23. Bakelite is used for making electrical switches, handles of various utensils, etc.

24. Melamine is used for making floor tiles, kitchenware, etc.

25. Plastic is a non-biodegradable substance. So, the articles made of plastics do not rot when they are thrown away after use. This pollute the environment.

26. When the plastic waste materials are burnt, they produce poisonous gases which pollute the air. The 4R principle, Reduce, Reuse, Recycle and Recover should be our basic mantra to minimise the hazards associated with the disposal of plastic wastes.

27. We must think twice before using plastic items.

Class 8 Science Chapter 3 Notes Important Terms

Acrylic: The synthetic fibre that resembles wool in its texture and properties is called acrylic.

Artificial silk: A man-made fibre obtained from chemical treatment of wood pulp which has properties similar to that of silk is called artificial silk.

Nylon: A fully synthetic polymer which is prepared from coal, water and air is called nylon.

Plastic: Those substances which are mostly synthetic in nature, obtained mainly from petrochemical sources and can be moulded into different shapes are called plastics.

Polyester: The synthetic fibre which is used for making PET bottles, home furnishings, etc., and are blended with natural fibres to enhance its properties is called polyester.

Polymer: The compound that are made up of small repeating units, joined together through bonds in a linear pattern is called polymer.

Polythene: The compound obtained from ethylene under high temperature, high pressure and in the presence of a catalyst is called polythene.

Rayon: A man-made fibre which is produced by the chemical processing of wood pulp, which is a natural substance is called rayon.

Synthetic fibres: The fibres which are made by human beings with the help of chemical substances are called synthetic fibres.

Terylene: A common variety of polyester which can be drawn into very fine fibres is called terylene.

Thermoplastics: Those plastics which soften on heating and hardened on cooling are called thermoplastics.

Thermosetting plastics: Those plastics, which when moulded once, cannot be softened again and lose their plasticity are called thermosetting plastics.

On this page, you will find Microorganisms: Friend and Foe Class 8 Notes Science Chapter 2 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 2 Microorganisms: Friend and Foe will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 2 Microorganisms: Friend and Foe

Microorganisms: Friend and Foe Class 8 Notes Understanding the Lesson

1. Microorganisms or microbes are extremely small living organisms which cannot be seen with the naked eyes.

2. Microorganisms can survive under all types of environment.

3. Microorganisms are broadly classified into four categories bacteria, fungi, protozoa and some algae.

4. Viruses are quite different from other microorganisms. They reproduce only inside the host organisms.

5. Some of the microorganisms are beneficial for us, while some are harmful for us.

6. Microorganisms are used in making curd, cake, bread, beverages, etc.

7. Out of several microorganisms contained in curd, the bacterium, Lactobacillus promote the formation of curd.

8. Yeast is a fungi which is used to convert sugar into alcohol. It reproduces rapidly and produces carbon dioxide during respiration.

9. The process of conversion of sugar into alcohol in the absence of oxygen is called fermentation.

10. Microorganisms are also used for producing antibiotics and vaccines. These antibiotics and vaccines stop the growth of other disease-causing microbes.

11. Some bacteria and blue green algae fixes atmospheric nitrogen into the soil. Thus increases soil fertility.

12. Microbes play the chief role in making of manures, which are useful for nourishment of soil.

13. Pathogens are disease-causing microorganisms that can enter our body through the air we breathe, the water we drink, and through direct contact with an infected person or through carriers.

14. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.

15. There are some animals and insects that transfer harmful disease-causing microbes from one body to the other, e.g., flies, mosquitoes, etc., These are called carriers.

16. Anthrax is a harmful human and cattle disease caused by a bacterium.

17. Some microorganisms spoil the food items by producing toxic substances on them. These make the food poisonous causing serious sickness and even death.

18. To save the food from the attack of harmful microbes, some chemicals called preservatives are used. Common preservatives used are common salt, sugar, edible oils, vinegar, sodium benzoate, sodium metabisulphite.

19. Milk is pasteurised for killing harmful microbes. It is heated to about 70° C for 15-30 seconds and then suddenly chilled and stored. This prevents the growth of harmful microbes. This process was given by Louis Pasteur. It is called pasteurisation.

20. Nitrogen Cycle: Some bacteria and blue-green algae present in the soil fix nitrogen gas from the atmosphere and convert it into nitrogenous compounds. These useful nitrogenous compounds are then used by plants from the soil with the help of their roots. They help in the synthesis of proteins and other compounds. On the other hand, there are some bacteria that convert some part of nitrogenous compounds into nitrogen gas again and send them back into the atmosphere.

21. Due to this, nitrogen cycle, the percentage of nitrogen gas in the atmosphere remains more or less constant.

Class 8 Science Chapter 2 Notes Important Terms

Algae: Algae is a vast group of simple, unicellular to multicellular, plant-like organisms which are often present in aquatic habitat, e.g., Chlamydomonas, etc.

Antibiotics: A type of medicine that kills or stops the growth of disease-causing microbes is called as antibiotics.

Antibodies: When harmful pathogens enter our body, our defense mechanism produces substance to fight them, which are called antibodies.

Bacteria: Very small single-celled microbes which have cell walls, but don’t have an organised nucleus and other structures.

Carrier: An animal or insect that transmits pathogens from an infected person to a healthy one is called a carrier.

Communicable diseases: The microbial diseases which can be spread from an infected person to a healthy one through air, water, food or physical contact, etc., are called communicable diseases.

Fermentation: The method in which sugar present in the food is converted into alcohol and carbon dioxide by the microorganisms in absence of oxygen is called fermentation.

Fungi: Fungi are vast groups of microbes which do not have chlorophyll and thus don’t photosynthesise, e.g., yeast, moulds, etc.

Lactobacillus: Bacterium present in curd which promotes its formation.

Microorganisms: Organisms which are too small, to be visible with the naked eyes are called as microorganisms. These include virus, bacteria, fungi, protozoa and a few algae.

Nitrogen cycle: The series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms, including nitrogen fixation and decomposition.

Nitrogen fixation: The process of conversion of atmospheric nitrogen into its usable forms.

Pasteurisation: The process in which the milk is heated to about 70°C for 15 to 30 seconds and then it is chilled suddenly and stored is called pasteurisation.

Pathogens: Pathogens are disease-causing microorganisms.

Preservation: The method used for prevention of spoiling of food by the action of microbes is called food preservation.

Protozoa: Group of single-celled microorganisms, which are also categorised as small animals are called protozoa.

Rhizobium: Bacteria which is present in the root nodules of leguminous plants and fixes atmospheric nitrogen in the soil is called Rhizobium.

Vaccine: Dead or weakened microbes that produces immunity against a disease causing microbe in the living body is termed as vaccine.

Virus: Viruses are microbes which are living only inside another living cell. They are considered intermediate between living and non-living.

Yeast: Yeast are unicellular microbes categorised under fungi are used in fermentation to produce wine, beer and other beverages.

On this page, you will find Crop Production and Management Class 8 Notes Science Chapter 1 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 1 Crop Production and Management will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Chapter 1 Notes Crop Production and Management

Crop Production and Management Class 8 Notes Understanding the Lesson

1. The branch of science that deals with growing plants and raising livestock for human use is called agriculture.

2. When plants of same kind are grown and cultivated at one place on a large scale, it is called a crop.

3. The products obtained from the crops are called produce.

4. The crops grown in India can be classified as kharif and rabi crops.

5. Kharif crops are sown in the rainy season by June/July, and are harvested by September/October. Thus, they are also known as summer season crops. For example, rice, maize, cotton, pulses, etc.

6. Rabi crops are sown in the winter season in October or November and are harvested by March/April. For example, wheat, potato, barley, etc.

7. Agricultural practices are those practices which involve the necessary steps to be taken during production of crops.

8.  Important steps that are taken during crop production are:

• Preparation of soil
• Sowing
• Adding manure and fertilisers
• Irrigation
• Protecting from weeds
• Harvesting
• Storage

9. The preparation of soil is the first step before growing a crop. One of the most important tasks in agriculture is to turn soil and
loosen it.

10. The loosening of soil allows roots to penetrate deep into the soil.

11. The process of loosening and turning of the soil is called tilling or ploughing. Ploughing is either done by a plough or a tractor.

12. Hoe is a simple tool which is used for removing weeds and for loosening the soil.

13. Levelling is the process of breaking down the larger lumps of soil, and then levelling it by using a leveller.

14. Sowing is the most important part of crop production. Before sowing, good quality of seeds are selected.

15. The tool used traditionally for sowing seeds is shaped like funnel. Nowadays the seed drill is used for sowing with the tractors. This tool sows the seeds uniformly.

16. Continuous growing of crops makes the soil poorer in certain nutrients.

17. The substances which are added to the soil in the form of nutrients for the healthy growth of plants are called manure and fertilisers.

18. Manure is an organic substance obtained from the decomposition of plant or animal wastes.

19. Fertiliser is a chemical substance which is rich in a particular nutrient. Fertilisers are produced in factories. Some examples of fertilisers are urea, ammonium sulphates, superphosphate, etc.

20. The use of fertilisers helps farmer to get better yield of crops such as wheat, paddy and maize whereas manure improves soil texture as well as its water retaining capacity.

21. Excessive use of fertilisers makes soil less fertile. Fertilisers also leads to water pollution.

22. The organic manures is considered better than fertilisers.

23. The supply of water to crops at different intervals is called irrigation.

24. The time and frequency of irrigation varies from crop to crop, soil to soil and season to season.

25. The sources of irrigation are wells, tubewells, ponds, lakes, rivers, dams and canals.

26. The various traditional ways for irrigation are:

• moat (pulley-system)
• chain pump
• dhekli
• rahat (lever system)

27. Modern methods of irrigation help us to use water economically. Modern methods of irrigation are sprinkler system and drip system.

28. Sprinkler system is more useful on the uneven land where sufficient water is not available.

29. In drip system the water falls drop by drop just at the position of the roots.

30. The undesirable plants that grow naturally along with the crop are called weeds. Weeds compete with the crop plant for nutrients, space and sunlight.

31. The process of removal of weeds is called weeding.

32. The growth of weeds is controlled by using certain chemicals, called weedicides.

33. Weedicides are sprayed in the field to kill the weeds.

34. The process of cutting of crop after it is mature is called harvesting.

35. Harvesting in our country is either done manually by using sickle or by a machine called harvester.

36. The process of separating the grain seeds from the chaff is known as threshing.

37. The process of threshing is carried out with the help of a machine called combine which is in fact a combined harvester and thresher.

38. Farmers with small holdings of land do the separation of grain and chaff by the process of winnowing.

39. The large scale storage of grains is done in silos and granaries to protect them from pests like rats and insects.

40. Animals reared at home or in farms, have to be provided with proper food, shelter and care. When this work is done at a large scale then the process is called animal husbandry.

Class 8 Science Chapter 1 Notes Important Terms

Agricultural practices: The activities carried out for cultivation of crops over a period of time are known as agricultural practices.

Animal husbandry: Animals reared at home or in a farm, have to be provided with proper food, shelter and care, when this is done on a large scale it is called animal husbandry.

Crop: The same kind of plants which are grown and cultivated at a place are known as crop.

Fertiliser: Fertiliser is a chemical compound which is very rich in plant nutrients like nitrogen, phosphorus and potassium.

Granaries: The storehouse or repository for grain after it has been threshed or husked.

Harvesting: The process of cutting the crop after it is fully mature is called harvesting.

Irrigation: The process of supplying water to crops at appropriate intervals is called irrigation.

Kharifi: The type of crops which are grown in the rainy season, that is from June to September, are called kharif crops.

Manure: The decomposed organic matter obtained from plant or animal wastes is called manure.

Plough: The device which is used for tilling and ploughing is called plough.

Rabii: The type of crops grown in winter season, that is from October to March, are called rabi crops.

Seed: A plant’s fertilised ovule from which a new plant may grow is called seed.

Silo: A tall tower or pit on a farm used to store grains.

Sowing: The process of putting seeds in the soil is known as sowing.

Storage: Storage is a process of keeping crop grain safe from moisture, insect and rats for longer time.

Threshing: The process of separation of grain from the chaff in the harvested plant is called threshing.

Weeds: The unwanted plants that grow along with the crop are known as weeds.

Weedicide: The chemicals sprayed to control the growth of weeds is known as weedicide.

Winnowing: The process of separation of grain and chaff is called winnowing.

On this page, you will find Management of Natural Resources Class 10 Notes Science Chapter 16 Pdf free download. CBSE NCERT Class 10 Science Notes Chapter 16 Carbon and its Compounds will seemingly help them to revise the important concepts in less time.

CBSE Class 10 Science Chapter 16 Notes Management of Natural Resources

Management of Natural Resources Class 10 Notes Understanding the Lesson

1. Natural resources: The resources provided by the nature and utilised by human beings are called natural resources. Example: Soil, air, water, forests, wildlife, coal, petroleum, etc. Management of Natural Resources is necessary for their conservation and sustainable development.

2. Efforts for Environment Protection: There are international laws and regulations; National laws and acts creating awareness and National and international organisations working towards protecting our environment.

3. Ganga Action Plan: A multi-crore project came about in 1985 to improve quality of the water in the Ganga.

4. Coliform: A group of bacteria found in human intestines. Its presence in water indicates contamination by disease-causing microorganisms.

5. Survey for Coliform Count in 1993-1994: The results of survey done in 1993-1994 for finding total coliform in terms of MPN/100 mL is:
Minimum desired level 450 MPN/100 mL; Minimum level found in Rishikesh 600-650 MPN/100 mL; Maximum level found in Kannauj 1400 MPN/100 mL.

6. Pollution of the Ganga: The Ganga runs a course of 2500 km from Gangotri in the Himalayas to Ganga Sagar in the Bay of Bengal. It is getting polluted due to the flow of garbage, excreta, untreated sewage which are dumped into it. Also, human activities like bathing, washing of clothes and immersion of ashes or unbumt corpses, chemical effluents from industries increase its pollution load. This leads to toxicity which kills fish in large sections of the river.

7. The three R’s to save the environment: Reduce, Recycle and Reuse.

8. Reduce: Use less and not to waste any resource.

9. Recycle: Segregate the waste that can be recycled and make required things by using them,

10. Reuse: Use the things again and again.

11. Reuse is better than recycling: Reusing helps to save energy, so it is better than recycling.

12. Concept of sustainable development: Encourage forms of growth and development which helps to meet current basic human needs while preserving the resources for the needs of future generations. In this way economic development is linked to environmental conservation.

13. Need to Manage Natural Resources: The human population is increasing at a tremendous rate due to improvement in health care, so the demand for all resources is increasing at an exponential rate. Since the resources are limited, the management of natural resources is necessary, so that these will last for the generations to come. This management would help in equitable distribution of resources and reducing the damage being done to the environment.

14. Biodiversity Hot Spots: Forests are biodiversity hot spots. Number of species found in an area is one of the measures of biodiversity along with the range of different life forms (bacteria, fungi, ferns, flowering plants, nematodes, insects, birds, reptiles, etc.)

15. Result of loss in biodiversity: Experiments and field studies suggest that a loss of diversity may lead to a loss of ecological stability.

16. Stakeholder: A person having interest or concern for something is called as stakeholder. The various stakeholders for the conservation of forests are:

• Local People: Those who are dependent on forests for their survival.
• Forest Department: Government who owns the land and controls resources
• Industrialists: Those who use various forests
• Wildlife enthusiasts: Those who want to conserve nature

17. Efforts of Bishnoi community in Rajasthan: Bishnoi community of Rajasthan has religiously being protecting the environment. ‘Amrita Devi Bishnoi National Award for Wildlife Conservation’ is given by the Government in the memory of Amrita Devi Bishnoi, who in 1731 AD sacrificed her life along with 363 others for the protection of‘khejri’ trees in Khejarli village near Jodhpur in Rajasthan.

18. Sustainable Management: The management of forest resources wisely and judiciously to fulfil needs of present generation as well as future generations.

19. The Chipko Andolan (‘Hug the Trees Movement’): This movement for conservation of forests originated in a remote village called Reni in Garhwal Himalayas during the early 1970s when the women of the village clasped the tree trunks thus preventing the workers of logging contractor from felling the trees.

20. People’s Participation in the Management of Forests: In 1972, the West Bengal Forest Department failed in reviving the degraded Sal forests in the south-western districts of the state by methods of surveillance and policing. Complete alienation of the people from the administration led to movements by the Naxalites and into frequent clashes between forest officials.

21. Due to efforts of forest officer A.K. Baneijee, villagers were involved in the protection of 1,272 hectares of badly degraded Sal forest. Villagers were given employment in both silviculture and harvesting operations, 25 per cent of the final harvest, and allowed fuel wood and fodder collection on payment of a nominal fee in return of such help in protection. By 1983, the previously worthless Sal forests in Arabari forest range of Midnapore district underwent a remarkable recovery and were valued ? 12.5 crores with the active and willing participation of the local community.

22. Water as a Resource
Reasons for failure to sustain water availability underground:
Loss of vegetation cover, diversion for high water demanding crops, and pollution from industrial effluents and urban wastes.

23. Dams
Advantages of Dams:

• Ensure the storage of adequate water for irrigation and generating electricity.
• Canal systems leading from these dams can transfer large amounts of water great distances. Disadvantages of Dams:
• No equitable distribution of water.
• Large number of people displaced without compensation.
• Huge amount of public money is involved without giving proper benefits.
• Loss of biological diversity and deforestation.

24. Criticisms about large dams: They lead to

• Social problems: They displace large number of peasants and tribals without adequate compensation or rehabilitation.
• Economic problems: They swallow up huge amounts of public money without the generation of proportionate benefits.
• Environmental problems: They contribute enormously to deforestation and the loss of biological diversity.

25. Narmada Bachao Andolan (‘Save the Narmada Movement’): The movement started against the raising of the height of the Sardar Sarovar Dam on the river Narmada.

26. Water Harvesting: Watershed management emphasises scientific soil and water conservation in order to increase the biomass production.

27. Aim: To develop primary resources of land and water to produce secondary resources of plants and animals for use in a manner that will not cause ecological imbalance.

28. Benefits of Watershed management:

• Increases the production and income of the watershed community
• Mitigates droughts and floods
• Increases the life of the downstream dam and reservoirs.

29. Various ancient methods of water harvesting:

• Khadins, tanks and nadis in Rajasthan
• Bundhis in Madhya Pradesh and Uttar Pradesh
• Kulhs in Himachal Pradesh
• Eris (tanks) in Tamilnadu
• Kattas in Karnataka
• Bandharas and tals in Maharashtra
• Ahars and pynes in Bihar
• Ponds in the Kandi belt of Jammu region
• Surangams in Kerala,

30. Purpose of Water Harvesting:

• To recharge the ground water beneath.

31. Advantages of water stored in the ground:

• It does not evaporate.
• Spreads out to recharge wells and provides moisture for vegetation over a wide area.
• Does not provide breeding grounds for mosquitoes like stagnant water.
• It is relatively protected from contamination by human and animal waste.

32. Coal and Petroleum

• They are generally called fossil fuels.
• They are formed from the degradation of biomass millions of years ago.
• They will be exhausted in the future no matter how carefully we use them.
• Petroleum resources will last for about forty years while coal resources will last for two hundred years.
• They contain carbon, hydrogen, nitrogen and sulphur.
• They produce carbon dioxide, water, oxides of nitrogen and oxides of sulphur on being burnt.
• Carbon monoxide is formed instead of carbon dioxide, when they are burnt in insufficient amount of oxygen.
• The oxides of sulphur and nitrogen and carbon monoxide are poisonous at high concentrations and carbon dioxide is a greenhouse gas.
• Increase in amount of carbon dioxide is leading to global warming.

33. Ways to use resources judiciously:

• Taking a bus, public transport or walking/cycling instead of a private vehicle.
• Using LED bulbs in homes instead of normal bulbs.
• Taking the stairs instead of lift.
• Wearing an extra sweater on cold days instead of burning fossil fuels for warmth.

Class 10 Science Chapter 16 Notes Important Terms

Natural Resources: The stocks of nature such as air, water, soil, forests and wildlife. Biodiversity: The diversity of life forms present on Earth.

Sustainable Management: The judicious and wise use of natural resources to fulfil needs of present generation and preserving them for needs of the future generations.

Coliform: Group of gram negative, rod shaped bacteria found in polluted water and in human intestine. Coliform Count: Measure of pollution level of a water body on the basis of presence of coliform bacteria.

Silviculture: Practice of growing trees. Helpful in replenishment of forests.

Monoculture: A culture of single type of plant or tree in an area of forest.

Deforestation: Cutting down trees.

Afforestation: Growing or planting trees.

Reforestation: Growing or planting trees in a deforested area which previously had trees and vegetation.