Chapter 13

                                                                    Our Environment 

Intext Questions :- (Page no. 212)

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

Ans. Trophic Levels :

— The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels.

— Example : A food chain operating in a grassland is given below:

Grass —–> Insects —–> Frog —–> Birds

In this food chain :

— Grass is first trophic level.

— Grasshopper is second trophic level.

— Frog is third trophic level.

— Eagle is fourth tropic level.

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

Ans. Decomposers help in decomposing the dead bodies of plants and animals and hence act as cleansing agents of the environment.

— Decomposers also help in putting back the various elements of which dead plants and animals are made, back into the soil, air and water for reuse by the producers like crop plants.

— They help in recycling of the nutrients.

— They decompose dead remains thereby providing space for new life to settle in the biosphere.

(Page no. 214)

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

Ans. The microorganism like bacteria and other decomposer organisms (called saprophytes) present in our environment are specific in their action. They break down the materials or products made from natural materials but do not break down man-made materials such as plastics. So, it is due to the property of decomposer organisms of being specific in their action that some waste materials are biodegradable, whereas others are non-biodegradable.

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

Ans. Biodegradable substances are decomposed by the action of micro organisms and decomposed materials are recycled through geo-chemical cycle.

— These substances keep the environment clean.

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

Ans. They cause air, water and soil pollution.

— They may cause bio-magnification in the food chain and end up in humans.

(Page no. 216)

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

Ans. Ozone (O3) is an isotope of oxygen, i.e., it is a molecule formed by three atoms of oxygen. 

— At the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiations from the sun. These radiations are highly damaging to organisms. Ultraviolet rays can cause skin cancer.

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

Ans. Recycling :

— The solid wastes like paper, plastics and metals, etc. are recycled.

Preparation of Compost :

Biodegradable domestic wastes such as left over food, fruit and vegetable peels and leaves of potted plants, etc. can be converted into compost by burying in a pit dug into ground.

                      

                                                                         Exercise 

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), (c), (d)

2. Which of the following constitute a food-chain?

(a) Grass, wheat and mango                                   (b) Grass, goat and human

 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 then the food chain would end and ecological balance would be affected.

— If the herbivores are killed, then the carnivores would not be able to get food and would die.

— If carnivores are killed, then the population of herbivores would increases to unsustainable level.

— If producers are killed, then the nutrient cycle in that area would not be completed.

5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?

Ans. The impact of removing all the organisms in a trophic level will be same. If the organisms of any trophic level be removed it will certainly damage the ecosystem. For example,

Grass → Grasshopper → Frog → Snake → Peacock

In this if all grasshoppers are killed/removed, frogs will starve and grass will reproduce in abundance. If snakes are removed, then the number of frogs will increase which will disturb the entire ecosystem.

6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

Ans. The pesticides and chemicals are absorbed by plants from the soil and enter the food chain. Being non-biodegradable they accumulate progressively at each trophic level. As human occupy the top level of any food chain, the maximum concentration of chemicals is found in our bodies. This is called biological magnification.

— The level of magnification will be different at different trophic levels, the maximum concentrations will be at the highest trophic level and the chemical will be less at lower trophic levels.

7. What are the problems caused by the non-biodegradable wastes that we generate?

Ans. It is a reason of biological magnification.

— It increases the pollution

— It pollutes the atmosphere

— It kills useful micro-organisms.

8. If all the waste we generate is biodegradable, will this have no impact on the environment?

Ans. The biodegradable waste produced by us will have the following effect on our environment.

— Some biodegradable substances such as cow-dug produce a foul odor, thus polluting the surrounding environment.

— Some biodegradable substances such as fruits and vegetables waste, serve as that breeding grounds of mosquitoes cause different diseases in the surrounding atmosphere.

9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Ans. Ozone layer in the strastosphere is very helpful in shielding harmful UV rays. In absence of ozone layer, heavy damage to organism may occur. It may cause diseases like skin cancer, cataract, reduced crop production etc. The damage is limited by UNEP (United Nations Environment Programme), it has – forged an agreement to freeze CFC production in 1986.