Haritima : The Environmental Society Of Hansraj College



Energy is the vital source of functioning of the planet and its mega biodiversity.

All the functions of an ecosystem are in some way interlinked with growth and regeneration of Biotic agents.

Biotic Agents: Components which are living in nature. For Example; Plants, animals, Homo sapiens.

The functioning of the ecosystem is based upon many biogeochemical cycles.


The cyclical process of nutrients like Carbon, Nitrogen, Oxygen and Carbon.


  1. Carbon cycle
  2. Nitrogen cycle
  3. Sulphur cycle
  4. Oxygen cycle
  5. Water Cycle


  • Carbon (C) occurs in an inorganic form.
  • Carbon is the building block of animal and plants tissues.
  • Carbon in atmosphere is present as CO2.
  • By the phenomena of photosynthesis, Plants absorb sunlight as well as carbon dioxide (stomata present in leaves).
  • Roots of plants absorb water.
  • Thus Glucose (Carbohydrates) are formed which is a carbon compound.
  • Plants release oxygen as a bi product of
  • Consumption of food prepared by Plants transfer carbon in subsequent trophic level.
  • Both plants and animals release carbon dioxide, thus restoration of carbon in atmosphere.
  • El Nino storms too release carbon.

Photosynthesis: process by which plants use sunlight,  water, and carbon dioxide to form sugars.

Human effects on Carbon cycle:

        Many humans’ activities like burning,  deforestation,  etc have increased the carbon content thus causing an imbalances in carbon cycle. Global warming and glacier eradication is a major impact of it.


  • Nitrogen is present in the atmosphere as N2 in large amounts.
  • Around 78% in atmosphere.
  • The nitrogen is taken up by plants and used in metabolism for biosynthesis of amino acids, proteins, vitamins etc.
  • After death of the plants and animals ( Biotic Agents) the organic nitrogen in dead tissues is decomposed.
  • It is broken down by saphrophytes, and absorb material content from dead organisms.
  • Several groups of Ammonifying bacteria converting organic -N into Ammonia and nitrifying bacteria like Nitrosomonas and Nitrobacter which convert them into simple nitrites and nitrates respectively, which are again used by plants.
  • Some bacteria like Pseudomonas convert nitrates, into molecular nitrogen or N2 by denitrification which is released back into the atmosphere.


  • Sulphur is though not dominant yet is very important in Biotic food chain.
  • Sulphur is present in two forms;
    • Atmosphere (as oxides of sulphur, hydrogen sulphide) ,
    • Rocks and sediments (as mineral pyrites).
  • Atmospheric sulphur plays an important role, as the oxides of Sulphur react with rain water producing sulphuric acid (H2SO4) which comes down as ‘acid rain’.
  • Acids rains are corrosive in nature.
  • Oxides of sulphur are released into the atmosphere due to burning of fossil fuels.
  • In the soil or water, there are different groups of micro-organisms which carry out oxidation and reduction of various sulphur compounds.
  • A special role is played by Thiobacillus bacterium, which converts sulphides into sulphuric acid.
  • These bacteria help in bio-leaching of metals from ores containing pyrites (S) as impurities.


  • Oxygen is the second abundant component in earth atmosphere.
  • Plants and animals take up oxygen during respiration.
  • Plants give out oxygen and animals consume it. Animals give out carbon dioxide and plants consume it.
  • Thus Oxygen cycle and Carbon cycle are interdependent.
  • Ozone Layer to some extent helps in oxygen production. (O3 -> O2 + O)

Humans effects on oxygen cycle:

Deforestation leads to eradication of trees. Plants are the vital source of oxygen and eradicating them will directly effect animals including humans.  Amazon rainforest is so enriched by plants that it is called ‘ lungs of the Earth’. But with passing time, the forest is burning due to mankind activities.


  • Water is an essential commodity in Earth’s biodiversity.
  • The water is evaporated from its primary sources like Lake, River, Deltas, Sea, etc.
  • This water travel in form of water vapour and reaches atmosphere.
  • They condense in clouds.
  • The dense and condense clouds come down to earth in form of precipitation.
  • Thus, the water bodies are recharged.
  • The cyclical process of water is important for sustaining life on the Earth.

Human effects on Water cycle:

The mankind has disturbed the water cycle by polluting water bodies from household and industrial discharges.  Thus permanently disrupting water resources.

Fact: The Earth has only 3% freshwater.

error: Content is protected !!