[3 Mark Questions]

Question 13 Marks

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

Answer

Ozone layer absorbs ultraviolet radiation of the sun which is very harmful to living organisms.
Damage to the ozone layer is a cause for concern because depletion of ozone layer allows harmful ultraviolet radiation to reach to the surface of earth, which may lead to skin cancer, cataract, etc.
To reduce the damage to the ozone layer, use of chlorofluorocarbons has been minimised.
In $1987$, the $UNEP$ – United Nations Environment Programme has
Passed an agreement to freeze $CFC$ production at $1986$ levels.
This will protect the ozone layer and subsequent effects of radiation.

Question 23 Marks

Explain how is ozone formed? State the significance of ozone layer.

Answer

Ozone layer is located at the higher levels of the atmosphere, i.e., in stratosphere.
Ozone is formed by the action of $UV$ (Ultra violet) radiation on oxygen ($O_2$) molecule.
The higher energy of $UV$ radiation convert some oxygen ($O_2$) molecules into free oxygen $(O)$ atoms.
These free oxygen atoms combine with the molecular oxygen and form a molecule of ozone ($O_3$).
$O _2 \xrightarrow[Photodissociation]{\text { UV }} OV + O$
Significance:
Ozone shields the surface of the earth from ultraviolet $(UV)$ radiation from the sun.
The ozone molecules absorb short wave-length $UV$ rays which are harmful to organisms.
Thus, it protects life on the earth.

Question 33 Marks

Explain in brief : Biomagnification

Answer

Living organisms depend on each other for their food requirement and form a food chain.
Through such food chain energy and nutrients move to upper trophic levels sequentially.
If any non-biodegradable substance enters in biotic factor of an ecosystem, its concentration progressively increases at higher trophic level.
The uncontrolled use of pesticides and other chemicals increases the amount of these chemicals in the soil or water bodies.
From soil or water they enter in the body of plants and then in the bodies of herbivores and carnivores.
As these chemicals are not degradable, they get accumulated progressively at each trophic level.
This phenomenon is known as Biological magnification.
As human beings occupy the top level in any food chain, the maximum concentration of pesticides gets accumulated in human body.
Therefore, though for increase of crop production we use such chemicals; we need to control their use.

Question 43 Marks

Explain food chain and trophic levels.

Answer

swa

Science [3 Mark Questions]