Carbon Cycle

Carbon Cycle

Carbon is a macro element present in all living cells. In microorganisms, they are present in all macromolecules like cell wall, cytoplasmic membrane, proteins and nucleic acids.

Reservoirs of Carbon:

Reservoirs are the storage places of nutrients that are present in nature. They store nutrients in large amounts for longer periods of time.

Atmospheric CO₂, dissolved carbon in oceans and freshwater, organic matter are actively cycled carbon reservoirs. Sediments and fossil fuels like coal, petroleum and natural gas are slowly cycled carbon reservoirs. Carbon is cycled between these reservoirs by the biochemical activities of micro organisms and other living things (Figure 11.1).

The different stages or processes involved in carbon cycle are

1. Photosynthesis

2. Decomposition

3. Methanogenesis

1. Photosynthesis

It is a process where atmospheric CO₂ is converted to organic carbon (CH₂O)n. This is carried out by higher plants, photosynthetic bacteria, cyanobacteria and algae using radiant energy from the sun. This can be explained by the equation,

where (CH₂O)_n represents the organic form of carbon (Example: Carbohydrates) which gets incorporated into the photosynthetic organisms. This organic carbon serves as food for herbivores and in turn for carnivores.

2. Decomposition

The organic matter fixed as a result of photosynthesis is eventually degraded by microorganisms to CO₂ during processes like respiration and decomposition. When aerobic and anaerobic organisms respire, CO₂ is released into the atmosphere. Much of the CO₂ is released when dead organisms decompose in the soil predominantly by the activities of soil microorganisms. Burning of fossil fuels also release CO₂ into the atmosphere.

3. Methanogenesis

It is an anaerobic process where CO₂ gets converted to CH₄ (methane) by strict anaerobes like methanogens (Example: Methanobacterium). Methanogens are a group of Archaebacteria found in anaerobic environments like swamps, marshes, rumen of ruminants, paddy fields and gut of termites.

Methane is converted back to carbondioxide by a process called Methylotrophy.