(a) State with reason the consequence of decrease in number of carnivores in an ecosystem.

(b) In a food chain, state the trophic level at which the concentration of harmful chemicals is maximum. Why is it so?

OR

How is ozone layer formed ? State its importance to all life forms on earth ? Why the amount of ozone in the atmosphere dropped sharply in the 1980s ?

(A) A carnivore is an organism that mostly eats meat or the flesh of animals. Sometimes carnivores are called predators. Organisms that carnivores hunt are called prey. Carnivores are a major part of the food web. If carnivores number decreased in the food chain then, it will affect all the other trophic levels also. It will lead to an increase in the number of herbivores. As a result, the number of plants will decrease and the amount of oxygen will also decrease in the atmosphere.

B. Biomagnification is the increasing concentration of a substance, such as a toxic chemical, in the tissues of tolerant organisms at successively higher levels in a food chain. In the 3rd or the 4th trophic level, the Biomagnification is maximum.

Humans acquire the maximum of it, as ultimately we are the biggest consumer of every product.

OR

Ozone (O3) is a molecule which is formed by three atoms of oxygen. At the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings. Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms.

These atoms then combine with the molecular oxygen to form ozone as shown—

The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.