NCERT Solutions for Class 10 Science Chapter 14 - Our Environment

Question 1:

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


Trophic levels. The various steps in a food chain where transfer of food (energy) takes place are called trophic levels. Producer formed by green plants form first trophic level in a food chain.
Food chain. It is a sequential list of one organism consuming the other.
A simplest form of food chain is represented as Producer ¾® Herbivore ¾® Carnivore Characteristics of food chain
1. It is always straight.
2. Shorter the food chain, greater is the available energy.
3. The number of steps in any food chain is restricted to four or five.
4. There is always unidirectional flow of energy in a food chain.

Question 2:

What is the role of decomposers in the ecosystem?


Decomposers feed on the dead bodies of plants and animals. They return the simple components to soil and help in making the steady state of ecosystem. Decomposers are essential component of an ecosystem. They create a balance in the environments. They are called natural changing agents.

Question 3:

Why are some substances biodegradable and some non-biodegradable?


Some substances such as paper, clothes, vegetables, wood etc. can be broken down into simple substances by the action of living organisms are said to be biodegradable. There are other substances such as metals, plastics etc. which cannot be broken down are termed non-biodegradable substances.

Question 4:

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


1. Biodegradable substances get simplified by the action of micro-organisms and the simple components are restored to environment.
2. They help in recycling i.e. Gobar gas plant is best example of recycling in which dung and faeces are utilized to produce gas for cooking and the remains form important manures.

Question 5:

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


1. The non-biodegradable substances add to the pollution.
2. Biomagnification of pesticides such as D.D.T. in the body of living system is very harmful.
3. Solid waste leads to generation of methane which is causing global warming.

Question 6:

What is ozone and how does it affect any ecosystem?


Ozone is a molecule formed by three atoms of oxygen in the presence of UV rays.
Ozone performs important function at the higher level of atmosphere. Ozone absorbs UV rays from the sun. Thus it protects the living system on earth.

Question 7:

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


1. Recycling of wastes
2. Reduction at source
3. Better management
4. Vermicomposting
5. Use of ecofriendly products such as disposable paper cups in place of plastic cups.

Question 8:

Which of the following groups contains only biodegradable items:

  1. Grass, flowers and leather
  2. Grass, wood and plastic
  3. Fruit–peels, cake and lime-juice
  4. Cake, wood and grass.

Fruit–peels, cake and lime-juice

Question 9:

Which of the following constitute a food-chain?

  1. Grass, wheat and mango
  2. Grass, goat and human
  3. Goat, cow and elephant
  4. Grass, fish and goat.

Grass, goat and human

Question 10:

Which of the following are environment-friendly practices?

  1. Carrying cloth-bags to put purchases in while shopping
  2. Switching off unnecessary lights and fans
  3. Walking to school instead of getting your mother to drop you on her scooter
  4. All of the above.

All of the above.

Question 11:

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


If we kill all the organisms in one trophic level, imbalances are created in the food chain. 2. The population of organisms in previous trophic level will increase. If we kill population of frogs in the following food chain, the population of insects will increase to a great level and in turn they will damage the green plants.
The population of organisms in the next trophic level will decrease, as they will starve.

Question 12:

What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Explain the phenomenon of ‘biological magnification’. How does it affect organisms belonging to different trophic levels particularly the tertiary consumers?


The phenomenon in which the harmful pollutants (such as pesticides) enter the food chain and get concentrated more and more at each successive trophic level of organisms is called biological magnification. The level of bio-magnification will be different at different trophic levels of the ecosystem. This can be illustrated by the following example:
A large number of toxic chemicals like pesticides, weedicides, insecticides and fungicides are used to protect the crop plants from pests and diseases. Some of these chemicals get mixed up with the soil whereas others get washed down into the surface water bodies like ponds, rivers, etc., and the underground water bodies.
Water in a pond, lake or river contain only a small amount (0.02 ppm) of the harmful chemicals. The algae (phytoplankton) and protozoa (zooplankton) which utilize this water, contain a higher proportion (5 ppm). The fish which feeds on these organisms has a still higher amount of 240 ppm. Birds which feed on these fish contain the highest amount (1600 ppm).
This is the reason why our food grains such as wheat and rice, vegetable and fruits and even meat contain varying amounts of pesticide residues. So, the highest trophic level at the extreme right of food chain has the maximum concentration of harmful chemicals in a food chain.
Therefore, we observe that as we go higher and higher in the food chain, the concentration of pesticides in the body of the organisms gradually increases. For example, in the above example, the biological magnification of harmful pesticides goes upto 8000 times from water to fish eating birds.

Question 13:

What are the problems caused by the non-biodegradable wastes that we generate?
Explain two ways in which non-biodegradable substances affect our environment.


Problems caused by non-biodegradable wastes
1. Non-biodegradable solid waste is a great environmental hazard.
2. Plastic and their waste products such as carry bags, waste glasses, bottles, cups, plates are most dangerous. They choke in drain.
3. They cause soil pollution and degrade the soil.
4. They prevent growth of vegetation when dumped undergound.
5. They cause water pollution making this water unfit for drinking.
6. The plastic wastes when mixed with municipal waste make them unfit for recycling.
7. Non-biodegradable substances may be inert and simply persist in the environment for a long time and may harm various members of the ecosystem.

Question 14:

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


If all the wastes are biodegradable they will help in maintaining the neat, clean, and stable environment.

Question 15:

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


Ozone layer absorbs ultraviolet radiation of the sunlight which is very harmful to human beings. If the ozone layer in the atmosphere is depleted, these radiations would reach the earth and would cause many damages such as skin cancer, genetic disorders in man and other living beings.
The steps taken to limit the damage of ozone layer are as follows:
1. Judicious use of aerosol spray propellants such as fluorocarbons and chlorofluorocarbons which cause depletion or hole in ozone layer.
2. Limited use of supersonic planes.
3. Control over large scale nuclear explosions.