NCERT Solutions for Class 10 Science Chapter 15 Our Environment

NCERT Intext Questions

Page Number 260

1. What are trophic levels? Give an example of 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

Our Environmentans1

Trophic levels in a food chain

Different trophic levels:

  1. Grass represents first trophic level, called producers.
  2. Grasshopper represents second trophic level, called primary consumers.
  3. Frog represents third trophic level, called secondary consumers.
  4. Eagle represents fourth tropic level, called tertiary consumers.

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

Ans. Various roles played by decomposers in ecosystem are:

  1. They decompose biodegradable substances to useful substance.
  2. They release nutrients into soil by decomposing dead and decaying matter to make soil fertile.
  3. They help in recycling of nutrient to the ecosystem.
Page Number 262

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

Ans. Bio-degradable substances: The waste material which can be converted into its simpler form by the biological action of decomposers are called biodegradable substances.

Example: All naturally produced materials such as paper.

Non-biodegradable substances: The material which can breakdown by the action of decomposers are called non-biodegradable substances.

Example: Synthetic substances such as plastic.

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

Ans. 1. Biodegradable substances such as plant and food waste can be used as humus after composting. This increases the fertility of soil.

2. These substances after decomposition, produce CO2 which is released back to the environment or atmosphere.

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

Ans. 1. They contaminate soil and water, as they cannot be decomposed, hence they remain in ecosystem and cause  pollution. Example: Pesticides.

2. These substances when accidentally eaten by animals can harm them and even cause death. Example: Polythene.

Page Number 264

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

Ans. Ozone is a molecule formed by combining three molecules of oxygen atom with molecular formula O3. It is present in stratosphere and provides protection against harmful rays coming from sun to earth such as ultraviolet

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

Ans. 1. Recycling: The solid wastes like paper, plastics and metals, are recycled.

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

NCERT Exercise Questions

1. Which of the following groups contain only biodegradable item?

  • (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

Explanation: Biodegradable material: Grass, flower, wood, lime juice.

Non-Biodegradable material: Leather, plastic. Both options (b) and (c) are correct.

2. Which of the following constitutes 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

Explanation: Grass acts as producer, goat acts as primary consumer and human acts as secondary or tertiary consumer in a food chain.

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 on her scooter
  • (d) All of the above
  • Ans. (d) All of the above

Explanation: All the above statements are environment friendly because it does not affect environment adversly.

4. What will happen if we kill all the organisms in one trophic level?

Ans. The food chain would end and ecological balance would be affected.

  1. If carnivores are killed, then the population of herbivores would increase to unsustainable level.
  2. If the herbivores are killed, then the carnivores would not be able to get food and would die.
  3. If producers are killed, then no tropic level is possible.

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. Yes, the impact of removing all the organisms in a trophic level is different for different trophic levels. For e.g., if plants are removed from a food chain, no organism will get food as plants are the primary producers in food chain. If primary consumers are removed from a food chain the secondary consumers will starve and die and producers are also affected and may die due to competition for space and nutrients.

It is not possible to remove a trophic level without causing damage to the ecosystem as they all are interlinked.

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

Ans. Biological magnification: 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 bio-magnification would increase as the trophic level increases and would be the highest for topmost trophic level. It would affect their biological process such as growth, reproduction, etc.

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

Ans. The problems caused by the non-biodegradable wastes are :

  1. They contaminate soil and water as they cannot be decomposed and deposit on the surface of earth and block the water and nutrients to go into the soil hence it causes soil and water pollution.
  2. These substance, when eaten by animals can harm them, and even cause death.

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

Ans. Biodegradable wastes need to be decomposed within a particular period of time or else the accumulation of waste will lead again to pollution and affect environment accordingly.

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 of concern because it prevents UV-radiation coming from sun to earth which causes skin cancer.

The steps that are being taken to limit this damage are very less or no use of chemicals which cause ozone depeletion. Such chemicals are CFCs (Chlorofluro carbons).