NCERT Solutions for Chapter 15 Our Environment Class 10 Science

NCERT Solutions for Class 10 Science Chapter 15 Our Environment

In Text Questions

Page No: 257

Q 1: Why are some substances biodegradable and some non-biodegradable?


Some materials are biodegradable because they can be decomposed by micro-organisms/decomposers. For example-substances like paper, vegetable peels can be decomposed by micro-organisms into organic compounds, hence they are biodegradable.

On the other hand, some substances are non-biodegradable because the micro-organisms/decomposers cannot break or decompose them. For example – polythene bag cannot be decomposed by micro-organisms/ decomposers and hence they are non-biodegradable.


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


Substances which can easily be broken down by the microorganisms are biodegradable substances.

Biodegradable substances can have both and bad effect on the environment.

Good effects:

  • They do not cause too much pollution as they’re broken down easily.
  • They can provide nutrients to the soil.
  • Biodegradable substance are natural so they do not cause harm when handled.

Bad effects:

  • When biodegradable substances are degraded, they can cause foul smell.
  • Biodegradable waste often attracts flies and other insects.


Q 3: Give any two ways in which non-biodegradable substances would affect the environment.


Two ways in which non-biodegradable substances would affect the environment are:

  1. Some of the non-biodegradable wastes convert the land into barren land and enter the food chain thus affecting a human being and other biotic components of the environment.
  2. Pesticides and other chemicals enter water and food chains. They affect the fertility of soil and harm all kind of living organisms. Human beings are harmed the most because they are at the top of the food chain.


In Text Questions

Page No: 261

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


Trophic levels are the steps in a food chain where transfer of food in the form of energy takes place between organisms. At each step in a food chain is an organism that forms the trophic level.

A food chain consisting of four trophic levels.

Grass > Grasshopper/insect > Frog > Snake > Peacock

Trophic levels (Producers) – Primary consumer)-(Secondary consumer)-(Tertiary consumer) in this food chain.

The grass is a producer (First trophic level). Insect / grasshopper is an herbivore and eats grass. Thus, the insect is at the second trophic level. Insect, in turn, is eaten by frog (Carnivores I). Thus frog is at a third trophic level. The frog is eaten by a snake (Carnivores II). Thus snake is at the fourth trophic level. Snake, in turn, is eaten by peacock (Carnivores III). Thus, the peacock is at the fifth trophic level.


Q 2: What is the role of decomposers in the ecosystem?


Decomposers play a vital role in the ecosystem as they breakdown the organic components of dead and decaying matter into simple inorganic substances. The organic matter is recycled in the ecosystem thus acting as a cleansing agent for the environment. Also, these inorganic elements return back the mineral elements into the soil to be re-used by plants for growth which helps in maintaining the fertility of the soil.

Nitrifying bacteria break down ammonia in soil to nitrates which act as fertilizer to the soil. The ammonia in soil comes from decomposition of dead plants and animals.


In Text Questions

Page No: 264

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


Ozone is an isotope of oxygen gas formed by the reaction of ultraviolet radiations with oxygen. It differs from oxygen in having three molecules (O3) instead of two. Ozone is formed when Ultraviolet radiations act on oxygen molecules. Oxygen molecules O2 are converted to ozone O3 when Ultraviolet radiations act upon them.

Ozone layer protects ecosystems by blocking the harmful ultraviolet radiations coming from the sun, reaching the earth and thus protecting from ailments like skin cancer, cataract and immunosuppression which occur when ultraviolet radiations reach humans. Use of chlorofluorocarbon is depleting the ozone layer and making it thinner which is allowing ultraviolet radiations to penetrate the earth and cause cancer, cataract and immunosuppression in humans and is also damaging plant life. It is important to stop the emission of CFC’s which are contributing to depletion of ozone layer, in order to save all forms of life.


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


It is very important to manage waste disposal. Methods used to reduce the problems of waste disposal are as follows:

  • Practicing 3 R’s of waste management- Reduce, Re-use and Recycle. Reduce the use of plastics and polythene bags, and use jute bags more. Throwing biodegradable and non-biodegradable waste into separate dustbins make it easier to be recycled. Making Re-use of plastic containers to fill household items. Using paper bags and recycled paper.
  • Composting- Preparing compost by putting the organic matter/ biodegradable waste into compost pits dug in the ground. The compost decomposes the material into fertilizers which help in increasing the fertility of soil.



Page No: 264

Q 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


(a), (c) and (d) groups contain only biodegradable items. Plastic in option (b) is non-biodegradable so option (b) does not contain biodegradable items. The groups (a (c) (d) have grass, flowers, leather, fruit peels, cake, lime juice, wood which are biodegradable.


Q 2: Which of the following constitute a food chain?

 (a) Grass, wheat and mango

(b) Grass, goat and human

(c) Grass, fish and goat

(d) Goat, cow and elephant


(b) Grass, goat and human constitute a food chain. Grass is an autotroph i.e. it produces its own food. Grass is eaten by goat which is a herbivore. Human beings are omnivores (they eat both meat and plant foods) so they eat meat of goat. Hence this is a food chain.

Grass (Producer) → Goat(Herbivore) → Human (Omnivore)

The other options are not proper food chains.


Q 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


All of the three activities a, b and c are environment friendly. Carrying cloth bags and not plastic bags is environment friendly because plastic is non-biodegradable and causes pollution after it has been discarded, whereas cloth is degradable and also it lasts longer than plastic.


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


If we kill all the organisms in one trophic level then the transfer of energy to the next trophic level will stop because of which the organisms at next trophic level will die gradually due to unavailability of food. Also it will cause over population of the organisms belonging to previous trophic level because their predators (consumers) will be killed. Thus, it will disturb the food chain completely.
For example- In a food chain = grass → deer → lions.

If all of the deer population is removed, no energy and food will be transferred to lion population (lion is carnivorous i.e. it obtains energy by eating flesh of other animals), as a result the lion population will either gradually die due to starvation or move into city and attack humans. Also, due to death of all deer population, the grass vegetation will increase because there will be no deer to eat them. The entire food chain and hence the ecosystem will be disturbed.


Q 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?


Yes the impact of removing all the organisms in a trophic level will be different for different trophic levels.

No, the organisms of any trophic level cannot be removed without causing any damage to the ecosystem.

This can be explained with the help of following example of a simple food chain.
Grass → Deer → Lion

  • If all the deer population from this food chain is removed, the lions will die out of starvation and the grasses will increase in number and turn the land into forests This is because there will be no deer to feed on, the lions will die; and there will be no deer to eat the grasses, the grasses will keep on growing.
  • If we remove all the lions from this food chain, the population of deer will increase in number and eat out all the grasses present, thus turning the land barren.


Q 6: What is biological magnification? Will the level of this magnification be different at different levels of the ecosystem?


The increase in the concentration of harmful chemically substances in the body of the living organism at each trophic level of a food chain is called as biological magnification Chemicals, pesticides and heavy metals move up the food chain, get into aquatic bodies and are eaten by organisms like fishes which are in turn eaten by hawks/eagles. This process where the chemical enters the food chain and increase in concentration with increasing trophic level is known as biological magnification.

Yes, this magnification level will be different at different trophic levels in the ecosystem. Taking an example of a food chain

Plant → Goat → Man.


The chapter is to learn the concepts of eco-systems, food chain, and waste management. The various components of an ecosystem are interdependent.  The producers make the energy from sunlight available to the rest of the ecosystem. There is a loss of energy as we go from one trophic level to the next, this limits the number of trophic levels in a food-chain. This concept of food chain and food web is discussed. Biological Magnification is the process of accumulation of pesticides or other harmful chemicals.