NCERT Class 10 Science Chapter 15 - Our Environment

Chapter 15 Our Environment

Intext Question and Answers
Question 1: What are trophic levels? Give an example of a food chain and State the different trophic levels in it.
Answer: Each level or step of the food chain forms a trophic level. The example of food chain is given below:

In this food chain, green plants are at the first trophic level and are known as producers. Deer, in this food chain, is at the second trophic level and is known as primary consumer. Tiger is at the third trophic level and is known as secondary consumer.

Question 2: What is the role of decomposers in the ecosystem?
Answer: Decomposers, in the ecosystem, help in decomposing the dead remains of plants/animals. By decomposing, decomposers help in keeping the environment clean. After decomposing dead remains, decomposers convert it into humus which help in plants growth.

Question 3: Why are some substances biodegradable and some non-biodegradable?
Answer: Certain substances are easily acted upon by the enzymes of saprophytes and get converted into simpler substances, hence are biodegradable. Whereas certain Substances (like plastics) can't be degraded by the action of enzymes and thus are called non-biodegradable.

Question 4: Give any two ways in which biodegradable substances would affect the environment.
Answer: Two ways in which biodegradable Substances would affect the environment are:
• The degradation of biodegradable substances may release certain gases in the atmosphere, hence polluting the environment.
• They may become the breeding sites for flies and many other pests. Thus causing disease.

Question 5: Give any two ways in which non-biodegradable substance would affect the environment
Answer: Two ways in which non-biodegradable substance would affect the environment are:
• As non-biodegradable substances don't degrade, they pollute the environment and make it unfit for survival of living forms of life.
• They block the transfer of energy and minerals in the ecosystem.

Question 6: What is ozone and how does it affect any ecosystem?
Answer: Ozone is a triatomic molecule, i.e., made up of three molecules of oxygen joined together. It's molecular formula is O₃.
Ozone can affect the ecosystem in following ways:
• It protects against ultraviolet rays, if present in stratosphere.
• Ozone dissipates the energy of UV rays by undergoing dissociation followed by reassociation.
2O₃ → 3O2 + Energy
• In atmosphere, ozone is highly toxic and cause injury to mucous membrane, eye irritation and internal haemorrhages in animals and humans.

Question 7: How can you help in reducing the problem of waste disposal? Give any 2 methods.
Answer:
• Recycling: The solid wastes like paper metals, plastics etc can be recycled.
• Preparation of compost: Biodegradable domestic wastes such as left over food, fruit and vegetable peels etc can be converted in compost by burying in a pit dug into ground.




Exercise Question and Answers
Question 1: Which 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
Answer: a) Grass, flowers and leather

Question 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
Answer: b) Grass, goat and human

Question 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
Answer: d) All of the above

Question 4: What will happen if we kill all the organisms in one trophic level?
Answer: If we kill all organisms in one trophic level, then the food chain would end and ecological balance would be affected.
• If the producers were killed, then the nutrient cycle of that area would not be completed.
• If the herbivores were killed, then the carnivores would eventually die of hunger (as there would be no food).
• If the carnivores were killed, then the population of herbivores would increase.

Question 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 of the ecosystem?
Answer: Yes the impact of removing all the organisms in a trophic level will be different for different trophic levels. The lower trophic level of an ecosystem has a greater number of individuals than the higher trophic levels. Removal of producers will affect all the organisms of successive trophic levels and it will threat their survival. The removal of higher trophic level will lead to increase in organisms of lower trophic level and the organisms of higher trophic level will die due to the shortage of food.
No, removal of all organisms of a trophic level will disturb the ecosystem. Killing of higher trophic level organisms will cause explosion in the population of lower level organisms. This will adversely affect the ecosystem.

Question 6: What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer: Biological magnification refers to the increase in the concentration of certain toxicants at each successive trophic level.
No the levels of magnification will not be same in all trophic levels. When the chemicals don't get degraded and get accumulated progressively at each trophic level, it leads to biomagnification. Biomagnification is more in organisms of higher trophic levels.

Question 7: What are the problems caused by the non-biodegradable wastes that we generate?
Answer: Some problems caused by the non-biodegradable wastes that we generate are:
• As non-biodegradable substance don't degrade, they pollute the environment and make it unfit for survival of living forms of life.
• They block the transfer of energy and minerals in the ecosystem.

Question 8: If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer: If all the waste is biodegradable, then there will be no accumulation of waste and the Earth would be a cleaner place to live. But, if this biodegradable waste is too large in amount then its slow degradation may lead to air pollution (due to release of gases) as well as water and land pollution.

Question 9: Why is damage to the layer a cause Ozone for concern? What steps are being taken to limit this damage?
Answer: Thinning of ozone layer present in strastosphere is called depletion of ozone layer. Due to depletion of ozone layer, harmful ultraviolet radiations can reach the surface of Earth, which may lead to skin diseases, cancer etc. To reduce the depletion of ozone layer, use of chlorofluorocarbons has been minimised. In 1987, the UNEP has passed an agreement to freeze CFC production at 1986 levels.