Introduction: The flow of energy is linear in ecosystems but its opposite nutrients go through a cyclical process. The nutrients are locked in the dead remains of organisms and come back into the soil by decomposers.

The recycling of these nutrients is called the biogeochemical or nutrient cycle. As we know about the biosphere, it is a closed system i.e. nutrients are neither imported nor exported.

There are two manners of the biogeochemical cycle:

  1. Reservoir pool: The reservoir pool stores large amounts of nutrients as atmosphere or rock.
  2. The cycle of components: Bio-geochemical cycles carbon, nitrogen, and water in the atmosphere.

Table of Contents

Carbon cycle

The carbon cycle is the biogeochemical cycle through which carbon is exchanged among the biosphere, geosphere, hydrosphere, and atmosphere of the earth.

Carbon is the major component of the biological compounds as well as a major component of many minerals.

carbon cycle

carbon cycle

Steps of the Carbon cycle

The carbon cycle follows various steps:

PhotosynthesisGreen plants in the presence of sunlight utilizes CO2 in the process of photosynthesis and convert the inorganic carbon into organic matter (food) and release oxygen. part of the food made through photosynthesis is used by plants for their own metabolism and the rest is stored as their biomass which is available to various herbivores, heterotrophs, including human beings, and decomposers as food.

Respiration – organisms cannot survive without respiration. Respiration is a metabolic process where food is oxidized to liberate energy, CO2, and water. from respiration, we get energy for carrying out life processes. Here carbon dioxide is released into the atmosphere.

DecompositionAll assimilated food cannot be absorbed completely by organisms, the major part is retained by organisms as their own biomass which becomes available to decomposers on their death. The dead organic matter is decomposed by microorganisms and CO2 is released into the atmosphere.

Combustion: Burning of biomass releases carbon dioxide into the atmosphere.

Human Activities: Human activities particularly from the beginning of the industrial era increasingly disturbed the Global carbon cycle. Large-scale deforestation and growing consumption of fossil fuels by rising numbers of industries, power plants, and automobiles are primarily responsible for increased emissions of carbon dioxide. It leads to increased concentration of CO2 in the atmosphere, which plays a major role in global warming.

Nitrogen cycle

Nitrogen is an essential component of protein and is required by all living organisms including human beings.

The atmosphere contains nearly 79% of nitrogen, but atmospheric nitrogen cannot be directly used by the majority of living organisms. Therefore, the cycling of nitrogen becomes very important for all living organisms.

nitrogen cycle

Nitrogen cycle

Steps for Nitrogen fixation

There are five main processes which essential for the nitrogen cycle, these are:

  • Nitrogen fixation
  • Nitrification
  • Assimilation
  • Ammonification
  • Denitrification

1. Nitrogen fixationIn this process conversion of gaseous nitrogen takes place into Ammonia, in this form it can be used by plants. Atmospheric nitrogen can be fixed by these methods-

Atmospheric fixation: Lightening, combustion, and volcanic activity help in nitrogen fixation.

Industrial fixation: At high temperatures (400degreeC) and high pressure (~200 atm.),

molecular nitrogen breaks into atomic nitrogen after which it combines with hydrogen to form ammonia.

Bacterial fixation of nitrogen: There are two types of bacteria

  1. Symbiotic bacteria e.g. Rhizobium in the root nodules of leguminous plants
  2. Free-living or symbiotic e.g. 1. Nostoc 2. Azobacter 3. Cyanobacteria can combine atmospheric or dissolved nitrogen with hydrogen to form ammonia. Cyanobacteria can be free-living or symbiotic.

2. Nitrification– In this process, ammonia is converted into nitrates or nitrites by Nitrosomonas and Nitrococcus bacteria respectively. Nitrobacter is a soil bacterium that can convert nitrate into nitrite.

3. Assimilation– Nitrogen fixed by plants is converted into organic molecules such as proteins, DNA, RNA, etc. in this process.

4. Ammonification– Nitrogenous waste produced by living organisms such as urea and uric acid. All these waste products and dead remains of organisms are converted into inorganic ammonia with the help of Ammonifying bacteria, through the process called ammonification.

5. Denitrification – The conversion of nitrates into gaseous nitrogen is called denitrification. This process is just the reverse of nitrification.

Water Cycle

Water is essential for the survival of organisms. As we know about 2/3rd of the earth’s surface is covered with water.

water cycle

water cycle

However, a very small fraction of this is available to animals and plants, and it is not evenly distributed on the earth.

  • Almost 95 % of the total water on the earth is chemically bound to rocks and does no cycling of this water.
  • Evaporation, condensation, and precipitation are the main processes involved in the water cycle.
  • Water from oceans, lakes, ponds, rivers, and streams evaporates by the heat energy of the sun.
  • Transpiration of huge amounts of water by plants also. Water remains in the vapor state in the air and forms clouds that drift with the wind.
  • Clouds come in contact with the cold air in the mountain regions above the forests and condense to form rain and precipitate which comes down due to gravity.
  • Through these processes, water cycles itself and gets able to use it.

HOMEOSTASIS OF ECOSYSTEMecosystem regulates its own species structure and functional processes. This capacity of an ecosystem of self-regulation is known as homeostasis.


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