NCERT Solution
Chapter- 15
Our Environment
Page No.
1. Why are some substances biodegradable and some non-biodegradable?
Answer:
Substances which can be acted upon by microorganism (decomposer) are called biodegradable.
For example- vegetable wastes, paper, cotton etc.
On the other hand, materials which are not acted upon by decomposers are called non-biodegradable.
For example- plastic, glass, polyethene etc.
2. Give any two ways in which biodegradable substances would affect the environment.
Answer:
(a) They will serve as breeding ground for flies and mosquitoes which are carriers of disease like cholera, malaria etc.
(b) They produce foul smell, thus causing air pollution.
3. Give any two ways in which non-biodegradable substances would affect the environment.
Answer:
(a) Excess use of non-biodegradable pesticide and fertilizers run off with rain water to water bodies causes water pollution.
(b) They may choke the sever system of city or town that may overflow over roads.
Page No.
1. What are trophic levels? Give an example of a food chain and state the different trophic level in it.
Answer:
Each step in a food chain constitutes a trophic level.
For example
Grass ————————⇒ Dear —————————–⇒ Lion
Trophic level I Trophic level II Trophic level III
2. What is the role of decomposers in the ecosystem?
Answer:
They decompose dead remains of plants and animals and their wastes organic products into simple inorganic substances which are released into the atmosphere for reuse by the plants. Thus, they help in recycling of materials.
Page No.
1. What is a ozone and how does it affects any ecosystem?
Answer:
Ozone is a form of oxygen. It has the molecular formula O3. It is present at a higher level in the atmosphere. It protects the ecosystem from the harmful effects of ultraviolet rays coming from the Sun. UV rays may cause skin cancer, cataract to us.
2. How can you help in reducing the problems of waste disposal? Give any two methods.
Answer:
The following measures can be adopted for reducing the problem of waste disposal:
(i) Reduce the volume of wastes by burning in incinerator.
(ii) Produce compost and biogas from biodegradable waste.
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