Lesson: Our Environment

Question: 1

Why are some substances biodegradable and some non-biodegradable?


Substances that can be broken into simpler soluble forms or decomposed by microorganism are biodegradable substances whereas substances that cannot be decomposed to simpler substances are non-biodegradable substances.

So, whether a substance can be decomposed or not make it biodegradable or non-biodegradable.

Question: 2

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


(a) Biodegradable substances such as, plant parts, kitchen wastes, etc. can be used as humus after composting to enhance the fertility of the soil.

(b) Carbon is an important constituent of the biodegradable substances. Carbon is released into the atmosphere after the substances are decomposed.

Question: 3

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


(a) Non-biodegradable wastes like plastic articles, glass articles, etc. are major pollutants of the environment.

(b) Non-biodegradable wastes like DDT, can pass from plants to animals and finally to human beings along the food chain.

Question: 4

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


The trophic level of an organism in a food chain is the number of steps it is away from the beginning of the chain. Typically, plants are at trophic level 1, the primary consumers form the second trophic level, the secondary consumers form the third, and the tertiary consumers form the fourth trophic level.

In the given image, grass is the producer. It is eaten by the grasshopper. So, the grasshopper is the primary consumer. Then the grasshopper is eaten by the frog, so the frog is the secondary consumer and lastly the frog is eaten up by the snake. Hence, the snake is the tertiary consumer.

Question: 5

What is the role of decomposers in the ecosystem?


The decomposers break down the biodegradable substances into simpler forms. This helps cleaning the environment and bringing nutrients back to the soil.

Question: 6

What is ozone and how does it affect any ecosystem?


Ozone is a gas molecule made up of three oxygen atoms. The ozone layer is a layer of gas present in the stratosphere. The layer is only three to five millimetres thick and protects us from the harmful effects of the ultraviolet rays which cause skin cancer and cataracts.

Question: 7

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


(a) Using catalytic converter: Catalytic converters should be fitted in the chimneys for reducing the amount of gaseous pollutants coming from the factories.

(b) Treatment of sewage: Sewage from the factories should be sent to the effluent treatment plants. Once the effluent is treated, the clean water can then be sent to the nearest water bodies and the sludge can be allowed to decompose.