* Bio-concentration of pesticides- The accumulation of harmful chemicals such as
pesticides in the living organisms like plants, animals, human beings, etc. unknownly
through the food chain is called bio-concentration of pesticides.
-> Pesticides- The poisonous chemical substances spread over crop plants to protect them
from pests (harmful small animals for plants) and disease is called pesticides.
Q)
How pesticides work?
-> When we spray pesticides over plants, it mix up with soil and water. After that, pesticides
absorbed by the roots of growing plants along with water and minerals. When herbivorous
animals eat plants then the pesticides goes into them and after it reaches to higher
trophic level organisms.
The pesticides goes into their body and accumulated it in direct way or indirect way.
* Biological magnification- The increase of concentration of harmful chemical substances
like pesticides in the body of a living organism at each trophic level of food chain is called
biological magnification.
Animals at higher trophic levels have higher concentration of toxins.
Ozone Layer
-> Ozone is made of three atoms of oxygen. So, its atomicity is 3. Ozone layer is largely found
in the stratosphere which is a part of our atmosphere from 12 km -50 km above sea level.
This region is called ozonosphere.
Ozone is deadly poisonous at the ground level. In other words, It act as a poisonous gas if
it is inhaled. It is denoted by O3.
It is a thin part of the Earth's atmosphere that absorbs almost all of the sun's harmful
ultraviolet light. It is formed by the action of UV rays on Oxygen gas in atmosphere.
Formation of Ozone layer
-> When UV rays of sunlight strike the O2 atoms which presence in the atmosphere then
it breaks and formed nascent O2 atoms or free O2 atoms.
Now, Free O2 atoms react with O2 molecules which also presence in the atmosphere and
formed ozone layer.
Note:- Ozone layer is a protective blanket around earth which absorbs most of
the harmful UV (Ultraviolet) radiation of the Sun, thus, protecting the living
beings of the Earth from health hazards like skin cancer, cataract in eyes,
weaken immune system, destruction of plants etc. The decline of Ozone layer
thickness in Antarctica was first discovered in 1985 and was termed as
OZONE HOLE.
Effect of UV-rays
* It causes skin cancer
* It damage the eyes by causing eye disease called cataract
* It damage the immune system by lowering the body resistance to disease
Note:- Cataract is a medical condition in which the lens of the eye becomes progressively
opaque, resulting in blurred vision.
Depletion of Ozone Layer
-> By using different types of chemical such as CFCs (chlorofluorocarbons) which are widely
used in refrigerators and AC as coolant, in fire
extinguisher, in aerosol sprayers, etc.
CFCs released into the air and react with ozone gas and then destroy it gradually. Due to this,
the Ozone layer of upper most atmosphere becomes thinner.
As a result, it allows more UV rays to pass through them and ultimately leads to depletion
of Ozone layer.
Note:- A single chlorine atom can destroys 1,00,000 Ozone molecules. So, U.N.E.P. (United
Nation Environment Programme) did an excellent job in forging an agreement to freeze
CFC production at 1986 levels (KYOTO Protocol) by all countries.
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