Environment and biosphere: Every living organism has its own surrounding, medium of environment to which it interacts and is adapted to it. The environment is the sum total of physical or abiotic and biotic conditions influencing the organisms. The life supporting environment of planet earth is biosphere. The biosphere is composed of following three chief media:

  • Air
  • Water
  • Soil

These are the components of three major sub-divisions of the biosphere:

  • Atmosphere
  • Hydrosphere
  • Lithosphere

These media are not completely isolated from each other, however, some of the atmospheric gases are dissolved in all natural waters, and some moisture is present almost everywhere in the atmosphere.



 The envelope of gases made up of many layers surrounding the planet earth is called atmosphere. The atmosphere remains in contact with all the major types of environment of earth, interacting with them and greatly affecting their ability to support life. It filters sunlight that reaches the earth, affect climate, and is a reservoir of many essential elements.

The atmosphere is divided into five distinct layers:

  1. Troposphere: It is the innermost region of atmosphere. It is closest to the earth. Tropopause separates the stratosphere from troposphere and stratosphere.  It extends from the surface of the earth up to a height of 8 to 10 km at poles, 10 to 12 km at moderate latitudes and 16 to 20 km at the equator. In context to organism troposphere is the most important zone of atmosphere. All the climatic conditions takes place in troposphere. Air temperature in this zone gradually decreases with height at the rate of about 6.5% per km. In the upper regions of the troposphere the temperature decrease upto -60  ̊C.  
  2. Stratosphere: This is the second zone after Troposphere. About 30 km in height. Clouds and aeroplanes are found in its lower region. Temperature of this zone is up to 90  ̊C. This increase in temperature is due to presence of ozone layer formation because of ultraviolet component of sunlight. The layer of ozone is called ozonosphere. Upper layers of stratosphere forms stratopause.
  3. Mesosphere:  This zone is next zone after stratosphere. Which is 40km in height. Temperature of this zone decreases up to -80  ̊C. Upper layer of this zone from the mesopause.
  4. Ionosphere: The zone above mesosphere, up to the height of about 300 km above earth’s surface, is called ionosphere. It contains several layers of ionized air.
  5. Exosphere: It is the outermost zone of earth’s atmosphere and outer space begins after it. The air density is very low in this zone; hydrogen being dominant element of it.


The gaseous mixture of troposphere, it is utilized by most organisms in respiration to liberate energy from food during oxidation and is called air. Most air is persent up to the height of about 20km above earth’s surface i.e. 95%. The rest 5% is found about 280km height.


The oceans, rivers, streams, lakes, ponds, etc all the water sources form the hydrosphere. About 75% of earth’s surface is covered with hydrosphere, the main component of which is water.

The water remains in solid (snow), liquid (water) and gaseous (water vapour) forms. Water is most essential for the maintenance of all life.

Water is one of the main agent in soil formation ( pedogenesis)and is the media of several different ecosystem.

The two chief aquatic ecosystems- marine environment and fresh environment of earth are formed by mainly two water forms, salt water and freshwater.

Some physio-chemical properties of water:

  1. Viscosity: Water is fairly viscous liquid. The organisms which live in water have streamlined body, because the resistance to motion in a viscous medium is high. Due to high viscosity of water, it protects the aquatic animals and plants from the mechanical disturbances.
  2. Buoyancy: Water is a buoyant medium. Organisms can exist in it without specialized supportive structures.
  3. Transparency: Water is a transparent substance. Its transparency let the light penetrate to a depth.
  4. Pressure:  Organisms living at sea level experience a pressure of about 15psi, which is defined as 1 atm (760mm of Hg). Pressure influences solubility, ionic dissociation and surface tension, and water is slightly compressible with increased pressure.
  5. Salinity: The total amount of solid material in grams contained in one kilogram of the water, when all the carbonate has been converted into oxide, bromine and iodine replaced by chlorine and all organic matter completely oxidized.

Stenohaline, tolerate only narrow fluctuations in salinity of water.

Euryhaline,withstand wider ranges of salinity of water.



The solid component of earth is called lithosphere. The lithosphere consists of many layers.

  • Crust
  • Mantle
  • Outer core
  • Inner core

The core is innermost central fluid or vaporised sphere. Its diameter is about 2500 kms . Mainly composed of Nickel-Iron.

The mantle’s extends about 2900 kms above core. This is the molten state.

The outer most solid zone of the earth is called crust, which is about 8-40 kms above the mantle.



Soil is mixture of inorganic and organic materials, both of which are decomposition products.

Process of soil formation

  1. Weathering of Soil Forming Rocks: Soil formation is started by disintegration or weathering of rocks by some physical, chemical and biological agents, because of which the soil forming rocks break into small particles.
  2. Mineralization and humification: The breakdown organic debris into humus is accomplished and finally mineralization.  The residual amorphous, incompletely decomposed black colored organic matter which undergo mineralization is called humus. The process of humus formation is called humification.
  3. Formation of Organo-Mineral Complexes: Some colloidal humus particles may become associated with mineral particles to form organo-mineral complexes. The organo-mineral complexes are formed by two mechanisms , electro chemical and cementing.  

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