NCERT Class X Science Solutions: Chapter 15 – Our Environment Part 1

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Question 1:

Which of the following groups contain 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


C. Fruit-peels, cake and lime-juice

D. Cake, wood and grass

Substances that are broken down by biological processes are said to be biodegradable. In our environment, many of the substances are broken easily by decomposers as they possess specific enzymes for such activity.

Question 2:

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


B. Grass, goat and human

Food chain refers to the sequence of events in an ecosystem, where one organism eats another and then is eaten by another organism. It starts with the primary source like and sun or grass where producers make food, continues with consumers or animals who eat the food, and ends with the top predator.

This picture shows a food chain of human

A Food Chain of Human

Question 3:

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


D. All of the above

Environmentally friendly are sustainability and marketing terms referring to goods and services, law, guidelines and policies that claim reduced, minimal, or no harm upon ecosystems or the environment.

Eco-friendly products also prevent contributions to air, water and land pollution.

Question 4:

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


If we kill all the organisms in one trophic level, the transfer of food energy to the next trophic level will stop. This will cause a break in the food chain resulting in ecosystem imbalance. As a result, the organisms of the higher trophic level will also die, while the individuals of the lower trophic level will exhibit enormous growth in their population. Both the conditions will result in ecological upset.

This diagram shows trophic levels

Trophic Levels

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 to the ecosystem?


Yes, the impact of removing all organisms in a trophic level will be different for different trophic levels. If all the producers are killed, it will cause death or migration of the primary consumers in the ecosystem. In the absence of producers, subsequent level of consumers will also be affected. But if primary consumers are removed, organisms of higher trophic level will die, while those of lower level (producers) show exponential growth much beyond the carrying capacity of the environment. Removal of the organisms in a trophic level will upset the whole ecosystem as all categories of organisms are linked through food chain. The survival of organisms of one trophic level depends on the existence of the members of other trophic level.

Question 6:

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


Progressive increase in the concentration of non-biodegradable substances in a food chain is called biological magnification. The level of these harmful substances will go on increasing from one trophic level to the next. When certain harmful substances enter the food chain at the level of primary producers,-they get concentrated many times at each subsequent trophic level.

This picture shows energy flow in ecosystem

Energy Flow in Ecosystem

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