• All living organisms require Carbon, Hydrogen, Oxygen, Nitrogen,Sulphur, Phosphorous, Potassium and Calcium in large amounts.
  • They get the nutrients from air (Atmosphere) water (Hydrosphere) and soil (Lithosphere).
  • The nutrient elements derived from the earth by the living organisms for use in their growth and development are called bio-geo chemicals.
  • The cyclic flow of elements or compounds between non-living environment (soil, rock, air, water) and living organisms is known as bio- geo chemical cycle.

Life and Non-Life Interactions (Biotic and Abiotic Factors)

  • The branch of biology which deals with the interr-relationships oforganisms and their environment is called Ecology
  • The organisms and the physical environment of the habitat form anecological complex termed ecosystem
  • Ecosystem (Environmental system) includes two essential components:
  1. Abiotic components
  2. Biotic components

Abiotic Components

  • The abiotic components of the environment are air, water, soil, light andtemperature.

Biotic Components

  • Include all living organisms including human beings. Plants and animals are interdependent.
  • Bees depend for their food on pollen and nectar from flowers.
  • Flowers depend on bees for pollination. ‘=
  • The energy trapped by green plants is relayed through a series of heterotrophic organisms. This forms the food chain.
  • Grass – Rabbit – Fox – Tiger

Water Cycle

  • Oceans are the biggest store houses of water from which water evaporates to form clouds.
  • Plants absorb water from the soil or water reservoir and add it to the air (atmosphere) as vapour by transpiration.
  • Mammals excrete water as sweat which evaporates from their bodies.
  • Water is also added to the environment by death and decay of organisms.
  • About two-thirds of our body is made up of 97% oceans, 2% of ice-caps, 1% fresh
  • ground water. .
  • In 20 minutes, one thunderstorm can send down over over 125,000,000 gallons of water. (One gallon is equivalent to 4.5 litres)

Nitrogen cycle

  • Nitrogen is essential element required by organisms to synthesizeproteins and nucleic acids
  • Though atmosphere contains about 78% of Nitrogen, it cannot be utilizedby living organism unless it is converted into ammonia, amino acids or These compounds which are available in the soil are cycled andrecycled through the ecosystem.
  • The Nitrogen Cycle involves

Nitrogen fixation

  1. Nitrogen assimilation
  2. Ammonification
  3. Nitrification
  4. Denitrification

Nitrogen fixation

  • During nitrogen fixation, nitrogen is oxidized to oxides by lightningthese oxides get dissolved in rain water and get precipitated.
  • The nitrogen fixing bacteria such as Azotobacter, Rhizobium and blue green algae like Noshoc convert gaseous nitrogen to ammonia and nitrates

Nitrogen assimilation

  • The nitrates absorbed by plants is utilized for making organic matter suchas proteins, nucleic acids etc.


  • When the plants and animals die, their protein are broken down to release ammonia by the action of bacteria and fungi


  • The ammonia is converted into nitrates and nitrates by soil bacteria such as Nitrobacter and Nitrosomonas which are then absorbed by plants


  • Free living soil bacteria such as pseudomonas reduce nitrate ions of soil into gaseous nitrogen

Organisms involved in Nitrogen cycle


Name of organism

Nitrogen Fixation

Rhizobium, Azotobacter and Nostoc



Ammonifying bacteria and fungi



Nitrosomonas and Nitrobacter






Carbon Cycle

  • The three main sources of carbon are
  1. CO2 of the air and CO2 dissolved in oceans
  2. Carbonate rock in the earth’s crust and
  3. Fossil fuels like coal and petroleum
  • The atmospheric carbon dioxide enters into the living world, i.e, greenplants, through the process of photosynthesis.
  • The respiratory activities at each trophic level return carbon dioxidequickly to the atmosphere.
  • Carbon dioxide is also returned to the atmosphere through decomposition of dead organic materials, burning of fossil fuels volcanic activities.

Oxygen Cycle

  • All living organisms require oxygen for respiration Oxygen isone of theconstituents of water and forms about 20% of the air in the atmosphere.
  • Oxygen enters the living world through respiration
  • The carbon dioxide is utilized by the plants to produce food materials during the process of photo synthesis and oxygenisreleased.
  • These compounds after breaking down, release oxygen in the atmosphere and maintain balance in the Environment
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