Text-book Questions

Page no. 257 

Q1. Why are some substances biodegradable and some non-biodegradable?

Ans: Non-biodegradable substances are those which are decomposed by small organisms into simpler substances in a biological process. In contrast, non-biodegradable substances remain for a long time. They do not know how to decompose and they are harmful.

Q2. Give any two ways in which biodegradable substances would affect the environment.

Ans: (i) The decomposition of organic matter makes the atmosphere smelly.

(ii) Some toxic gases are produced during their decomposition such as - CO₂, it pollutes the environment.

Q3. Give any two ways in which non-biodegradable substances would affect the environment.

Ans: (i) Non-biodegradable substances remain in the environment for a long time due to not being decomposed, hence polluting the environment.

(ii) They are spreading dirt on the earth. These are also affecting the sewerage system. Example - plastic bags.

Page no. 261

Q1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Ans: The chain of organisms participating at various biological levels forms the food chain.

Each of its stages forms a trophic level.

Grass - worm - frog - snake - vulture

(a) Grass is the first trophic level of the food chain. It prepares its own food.

(b) The worm is the second trophic level of the food chain.

(c) Frog is the third trophic level and it eats grass.

(d) Snake is the fourth host of this chain.

(e) Vulture is the fifth and end host level of this chain.

Q2. What is the role of decomposers in the ecosystem?

Ans: Micro-organisms like bacteria and fungi etc. scavenge the residue. These organisms convert complex organic substances into simple inorganic substances. These substances are absorbed by the soil, so these micro-organisms help in recycling and protect the environment from dirt.

Page no. 264 

Q1. What is ozone and how does it affect any ecosystem?

Ans: Three atoms of oxygen combine to form one molecule of ozone O3. The ozone layer is in the upper surface of the atmosphere, it absorbs the harmful ultraviolet radiations of the sun. Therefore, ozone protects us from many diseases like skin cancer, ulcers etc.

Q2. How can you help in reducing the problem of waste disposal? Give any two methods.

Ans: (i) We should use organic matter instead of inorganic material. We should use paper or jute bags instead of plastic bags.

(ii) Organic waste should be disposed of in a place where it can be ready for recycling.