1 Why are some substances biodegradable and some non-biodegradable?
Substances which can be acted upon by microorganisms (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.
(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.
(a) Excess use of non-biodegradable pesticides 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.
4 What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Each step in a food chain constitutes a trophic level.$\\$ For example:$\\$ Grass $\rightarrow$ Dear$\rightarrow $ Lion$\\$ Trophic level I $ \ \ \ \ $ Trophic level II $ \ \ \ $Trophic level III
5 What is the role of decomposers in the ecosystem?
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.