NCERT SOLUTIONS
Chapter 15. Our Environment
QUESTIONS
Page No. 257
1. Why are some substances biodegradable and non-biodegradable ?
Ans: Biodegradable Substances: Some substances which are degraded and broken down into simpler substances by microorganisms are called biodegradable substances .
Example: Cotton, wood , paper etc.
Non-biodegradable Substances: Some substances which are not degraded or cannot be broken down into simpler substances by microorganisms are called non-biodegradable substances .
Example: Plastics .
2. Give any two ways in which biodegradable substances would affect the environment .
Ans: Some ways in which biodegradable substances would affect the environment are
(i) During decomposition process of biodegradable substances foul smell and some harmful gases released which make problem for the environment .
(ii) During decomposition it provide a breeding ground for mosquitoes, insects, and microbes responsible for diseases like cholera, diarrhoea etc .
(iii) Biodegradable substances increase humus in the soil and enhance soil fertility .
(iv) Biodegradable substances can spread various diseases by polluting water .
3. Give any two ways in which non-biodegradable substances would affect the environment .
Ans: Some ways in which non-biodegradable substances would affect the environment are
(I) Non-biodegradable substances do not decompose easily so it produces soil and water pollution .
(ii) These substances when accidentally eaten by stray animals can harm them and can even cause their death .
QUESTIONS
Page No. 261
1. What are trophic levels ? Give an example of a food chain and state the different trophic levels in it .
Ans: The various steps or levels in a food chain at which the transfer of food take places are called trophic levels .
A food chain operating in a grassland is given below
Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers
Grass → Insects → Frog → Snake
2. What is the role of decomposers in the ecosystem ?
Ans: The role of decomposers in the ecosystem are
(i) They act as cleansing agent of the environment by decomposing dead plants and animals .
(ii) They help in recycling nutrients .
(iii) They provide space for new beings in the biosphere by decomposing the dead .
(iv) They help in putting back the various elements into water, soil, and air for the reuse of producers like crop plants .
QUESTIONS
Page No. 264
1. What is ozone and how does it affect any ecosystem ?
Ans: Ozone (O3) is a molecule formed by three atoms of oxygen . It is a deadly poison .
At higher levels of the atmosphere ozone performs an essential function .
It shields the surface of the earth from ultraviolet (UV) radiation from the Sun . This radiation is highly damaging to organisms . For example, it is known to cause skin cancer in human beings .
2. How can you help in reducing the problem of waste disposal ? Give any two methods.
Ans: Some methods of reducing the problem of waste disposal are
(i) By increasing the use of biodegradable substances and by reducing the use of non-biodegradable substances we can reduce the problem of waste disposal .
For example: Instead of using plastic bags we should use paper bags or cloth bags etc.
(ii) By separating biodegradable and non-biodegradable waste before dumping them we can reduce the problem of waste disposal .
(iii) By recycling the non-biodegradable waste material we can reduce the problem of waste disposal .
EXERCISES
Page No. 264
1. Which of the following groups contain only biodegradable items ?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Ans: (a) Grass, flowers and leather
2. Which of the following constitute a food-chain ?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Ans: (b) Grass, goat and human
3. Which of the following are environment-friendly practices ?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
Ans: (d) All of the above
4. What will happen if we kill all the organisms in one trophic level ?
Ans: If we kill all the organisms in one trophic level, the food supply to the next level will stop, resulting in an imbalance of the ecosystem . As a result, animals in the upper levels will die, making growth of animals in the lower trophic level increases in an enormous way . All of this will affect the overall balance in the ecosystem .
5. Will the impact of removing all the organisms in a trophic level be difficult for different trophic levels ? Can the organisms of any trophic level be removed without causing any damage to the ecosystem ?
Ans: Yes, the impact of removing all the organisms in a trophic level will be difficult for different trophic levels . For example, on removing producers, herbivores would not be able to survive or they would migrate and the ecosystem would collapse . If herbivores are removed, producers would grow unchecked and carnivores would not get food .If carnivores are removed, herbivores would increase to unsustainable levels and could destroy the producers . This cause imbalance of the ecosystem of athat place . Thus to maintain the balance of the ecosystem the presence of all the organisms is necessary at each trophic level .
6. What is biological magnification ? Will the levels of this magnification be different at different levels of the ecosystem ?
Ans: The increase in concentration of harmful chemical substances like pesticides in the body of living organisms at each trophic level of a food chain is called biological magnification .
Yes, levels of biological magnification would increase as the trophic level increases and would be the highest for the topmost trophic level and minimum at the lowest trophic level .
7. What are the problems caused by the non-biodegradable waste we generate ?
Ans: The problems caused by non-biodegradable waste we generate are
(i) Since these substances can not be decomposed by microorganisms so reducing soil fertility .
(ii) Non-biodegradable substances do not decomposes easily so it produces soil and water pollution .
(iii) These substances when accidentally eaten by stray animals can harm them and even cause their death 8. If all the waste we generate is biodegradable, will this have no impact on the environment ?
Ans: If all the waste we generate is biodegradable, it will also have impact on the environment . If it is disposed off properly, the problem of air, water and soil pollution can be less to an extent . There would be less health problems and humans would be disease free . But if it is not disposed off properly, it will affect the environment adversely .
9. Why is damage to the ozone layer a cause for concern ? What steps are being taken to limit this damage ?
Ans: The damage to the ozone layer is a cause for concern because if the ozone layer in the atmosphere disappears completely, then all the extremely harmful ultraviolet radiations coming from the Sun would reach the earth .These ultraviolet radiations would cause skin cancer and other ailments in humans and animals and also damage the plants .
In an attempt to protect the ozone layer, the United Nations Environment Programme (UNEP) unanimously forged an agreement among its member countries to freeze CFC production at 1986 levels .
ADDITIONAL QUESTIONS
1. What is eco-system ? What are its components ?
Ans: All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem .
The components of a eco-system are
(i) Biotic Components: All living organisms in a eco-system are called biotic components .
Example: Plants and animals
(ii) Abiotic Components: All non-living components in a eco-system are called abiotic components .
Example: Air, water minerals etc.
2. What is food web ?
Ans: In an eco-system each organism is generally eaten by two or more other kinds of organisms which in turn eaten by several other organisms . So instead of a straight food chain, the relationship can be shown as a series of branching lines called a food chain .
3. What is food chain ?
Ans: A food chain s a linear sequence of organisms through which nutrients and energy pass as one organism eats another .
4. What is biological magnification ?
Ans: Biological magnification is the phenomenon in which harmful chemicals such as pesticides and other chemicals enter the food chain and its concentration increases progressively at each trophic level .
It is maximum at the heighest trophic levels and mimimum at lowest trophic levels . It is the highest in humans and lowest in autotrophs like plants.
5. How ozone is formed ?
Ans: Ozone is formed by the action of UV radiations on oxygen (O2) molecules at the higher levels of the atmosphere . The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms .These atoms then combine with molecular oxygen to form ozone as shown .
O2 + UV → O + O
O + O2 → O3
6. What are the factors that affect ozone layer ?
Ans: Chlorofluorocarbons (CFCs), Chlorine (Cl2), Nitrous oxide (N2O), and Methane (CH4) .
7. How does the depletion of ozone layer can be reduced ?
Ans: The steps that can be used to reduce for depletion of the ozone layer are
(i) By reducing the use of CFCs .
(ii) By using alternatives CFCs .
8. Whai is the full form of CFC ?
Ans: Chloroflurocarbon .
9. On which day conservation of ozone layer is observed ?
Ans: 15th September .
10. What is the first trophic level in a food chain ?
Ans: Producers (Autotrophs) .
11. What are decomposers ?
Ans: The microorganisms which can break-down the complex organic substances into inorganic substances that go into the soil and are used up once more by the plants are known as decomposers .
Example: Fungi and bacteria .
12. What are the harmful effects that can be produced by the depletion of ozone layer ?
Ans: The harmful effects that can be produced by the depletion of ozone layer are
(i) By the depletion of ozone layer can cause skin cancer to human beings .
(ii) It can damage aquatic plants and animals .
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