B.Sc.Part 3 Botany Semester v

1. SEMESTER V
UNIT V
Atmosphere – Gases Composition
BY
Dr.Vanita Uttamrao Pochhi
Shri Shivaji Science and Arts
College,Chikhli Dist.Buldana

2. Atmosphere
Each and every living organism has its specific surrounding
medium of environment to which it continuously interacts and
remain fully adopted.
The life supporting environment of planet earth the biosphere
is composed of three chief media.
Atmosphere (air)
Hydrosphere(Water)
Lithosphere (Soil)

4. Structure of Atmosphere
There are five concentric layers within the
atmosphere which can be distinguished on the basis
of Temperature.These are as follows.
1.Troposphere
2.Stratosphere
3.Mesosphere
4.Thermosphere
5.Exosphere

6. Troposphere
1. It is the lowermost layer.
2. The earths atmosphere from the surface upto about 20km.
3. Troposphere concerns us most because it is the only that supports
Plants and Animals .
4. The important weather events such as cloud formation
lightning, thundering, etc. take place in troposphere.
5. Air temperature in the zone gradually decreases with height
at the rate of about 6.50c per km.
6. The temperature might decrease upto -600c towards the upper
layer of the troposphere.
7.The water vapour in the atmosphere and most of the air is confined to
the troposphere. Troposphere merges into the next zone which is
known as Tropopause.

7. Stratosphere
1. It is the Second zone of about 30 km.in height where
temperature are about 900c .
2. In this zone the temperature shows an increase from a
minimum of about 50c.
3. Increase in temperature is due to ozone formation under the
influence of ultraviolet rays of solar radiation such a layer
of ozone is called Ozonosphere.
4. A large concentration of ozone (o3) is found in the stratosphere.This
Ozone layer absorbs much of the ultraviolet radiation emitted by the sun.
5. Stratosphere is above clouds ,violent stroms and precipitation. The
upper layer of the stratosphere form the stratopause

8. Mesosphere
1.It is the third layer of the atmosphere about 40 km in height
2. It extends to about 85 km.
3. This layer is often referred to as the cold layer .In this
zone temperature shows a decrease upto -- 900c .
3. The upper limit of the mesosphere is termed as mesopause.
4. Temperature once again grow colder as you rise up through
the mesosphere .
5.The air in the mesosphere is far too thin to breathe ,
6.Air pressure at the bottom of the layer is below 1% of the pressure
at sea level and continues dropping as you longer.

9. Thermosphere
1. Above the mesosphere the region is the Thermosphere .
2. This region is also called as Ionosphere .
3. The height is about 300km.which extends up to 500km
above the earths surface . Most of the gaseous component which
become ionised . They are rarely present in molecular form.
Thus radiant energy brings about considerable changes in the
atmosphere.
4. The layer of very rare air above the mesosphere is called
thermosphere.
5. High energy x rays and UV radiation from the sun are absorbed in the
layer

10. Exosphere
Exosphere is the region above the thermosphere .
It lacks atoms except that of hydrogen and Helium and extends
Up to 32190 km from the earth .
Exosphere has a very high temperature due to solar radiation.
It contains mainly oxygen and Hydrogen atoms.