Q.1“Damage to the ozone layer is a cause for concern.” Justify this statement. Suggest any two steps to limit this damage. ‘ [Delhi]
Answer. Ozone layer prevents the harmful ultraviolet radiation to enter the atmosphere and reach the earth’s surface. Depletion of ozone layer has become a cause for concern because it can cause serious effects on human body and other organisms of the environment like fatal diseases such as skin cancer, changes in genetic material DNA, eye damage, etc.
Two steps to limit this damage are as follows:

1. Judicious use of aerosol spray propellants such as fluorocarbon and chlorofluorocarbons which cause depletion or hole in ozone layer.
2.  Control over large scale nuclear explosions and limited use of supersonic planes.

Q.2  Explain the phenomenon of “biological magnification” How does it affect organisms belonging to different trophic levels particularly the tertiary consumers? [Delhi]
Answer. The process in which harmful chemicals enter a food chain and get accumulated progressively at each trophic level is called biological magnification.
Harmful and toxic chemicals enter our bodies when they are added to soil and water. Use of pesticides to protect the food crops from diseases and pests and chemical wastes of factories are dumped in open or disposed off into rivers. These chemicals are washed down into the soil and ultimately to water table or get absorbed or taken up from the soil by the plants along with water and minerals and in this way harmful chemicals enter the food chain. The quantity of these harmful chemicals increase with increase in trophic level of the food chain because these substances are not degradable. Man is at the top of the food chain, so concentration is maximum in human beings.
Thus, accumulation of DDT has been maximum in man as DDT is used to destroy pests. DDT is accumulated in the following way in this food chain:
This is the reason why our food grains such as wheat and rice, vegetables and fruits and even meat contain varying amounts of pesticides residues. So, the highest trophic level at the extreme right of food chain has the maximum concentration of harmful chemicals in a food chain.

Q.3 (a) What is ‘environmental pollution’?
(b) Distinguish between biodegradable and non-biodegradable pollutants.
(c) Choose the biodegradable pollutants from the list given below:
Sewage, DDT, radioactive waste, agricultural waste. [Delhi]
Answer. (a) Environmental pollution is an undesirable change in the physical, chemical or biological
characteristics of the natural environment, brought about by man’s activities. This pollution may affect the soil, rivers, seas or the atmosphere.

(c) Biodegradable pollutants are sewage and agricultural waste.

Q4 Which of the following groups contain only biodegradable items?
a. Grass, flowers and leather
b. Grass, wood and plastic
c. Fruit peels, cake and lime juice
d. Cake, wood and grass

Solution:

a) Grass, flowers and leather
c) Fruit peels, cake and lime juice
d) Cake, wood and grass

Above all are the groups that contain only biodegradable items. Since plastic is not a biodegradable substance, that group cannot be considered as a biodegradable.

 Q.5Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Solution:

The ozone layer is a protective cover for the earth. It prevents harmful UV rays from entering the earth as these rays harmful and can result in skin cancer. But the air pollutants like chlorofluorocarbons (CFCs) are the main reason for the depletion of the ozone layer. Too much of UV rays are harmful to plants as they affect photosynthesis, destroy planktons and decomposers. These are the reasons why damage of ozone layer is a cause of concern.

Q.6 Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment. [Delhi]
Answer. Bacteria and fungi breakdown the dead remains and waste products of organisms. These micro organisms are called the decomposers as they breakdown the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.
Two advantages of decomposers to the environment are as follows:

1. 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 by recycling of nutrients. They, therefore, create a balance in the environment.
2. They also act as scavengers or cleansing agents of the atmosphere.

Q.7. Describe how decomposers facilitate recycling of matter in order to maintain balance in the ecosystem. [Foreign]
Answer. Decomposers are micro organisms that obtain energy from the chemical breakdown of dead organisms of animals or plants. These micro organisms breakdown the complex organic substances of dead organisms into simple inorganic substances that go into the soil and are used up once more by the plants. Decomposers thus, help in recycling of matter.

 How is ozone formed in the upper atmosphere? Why is the damage of ozone layer a cause of concern to us? State a cause of this damage. [Delhi(C)]
Answer. Ozone is formed in upper atmosphere by the reaction of ultraviolet (UV) radiations on oxygen (0₂) molecule.
The damage to ozone layer is a cause of concern to us as due to its damage, more ultraviolet rays reach the earth’s surface causing various health hazards.

A cause of this damage is the presence of large amount of chlorofluorocarbons in the atmosphere.

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