Page 217 - NCERT Science Class 10 English Medium

and animals. This is one of the ways in which they enter the food chain.
As these chemicals are not degradable, these get accumulated
progressively at each trophic level. As human beings occupy the top
level in any food chain, the maximum concentration of these chemicals
get accumulated in our bodies. This phenomenon is known as biological
magnification. This is the reason why our food grains such as wheat
and rice, vegetables and fruits, and even meat, contain varying amounts
of pesticide residues. They cannot always be removed by washing or
other means.

Activity 13.313.3
Activity 13.3
Activity 13.3
Activity
Activity 13.3
n Newspaper reports about pesticide levels in ready-made food items
are often seen these days and some states have banned these
products. Debate in groups the need for such bans.
n What do you think would be the source of pesticides in these food
items? Could pesticides get into our bodies from this source through
other food products too?
n Discuss what methods could be applied to reduce our intake of
pesticides.

Q U E S T I O N S

1. What are trophic levels? Give an example of a food chain and state the
different trophic levels in it. ?
2. What is the role of decomposers in the ecosystem?

HOW DO OUR ACTIVITIES AFFECT THE
13.2 .2 .2 .2 HOW DO OUR ACTIVITIES AFFECT THEHOW DO OUR ACTIVITIES AFFECT THE
1 13 3 3
1 1 3 . 2 HOW DO OUR ACTIVITIES AFFECT THEHOW DO OUR ACTIVITIES AFFECT THE
E EN V I R O N M E N T ?
NVIRONMENT?
ENVIRONMENT?
E ENVIRONMENT?NVIRONMENT?
We are an integral part of the environment. Changes in the environment
affect us and our activities change the environment around us. We have
already seen in Class IX how our activities pollute the environment. In
this chapter, we shall be looking at two of the environmental problems
in detail, that is, depletion of the ozone layer and waste disposal.

13.2.1 Ozone Layer and How it is Getting Depleted

Ozone (O ) is a molecule formed by three atoms of oxygen. While O ,
3 2
which we normally refer to as oxygen, is essential for all aerobic forms of
life. Ozone, is a deadly poison. However, 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

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