Summary of what I learnt (Nutrient Cycle)

Carbon Cycle:

Carbon is found in all ecosystems, because all living things on Earth are composed of carbon compounds. The main source of carbon for all ecosystem is the atmosphere. The carbon cycle ensures continuous supply of carbon dioxide for plants to carry out photosynthesis and enables energy to flow through the ecosystem.

Carbon exchanges between the atmosphere and the biosphere occur through the following processes:

Photosynthesis:

Carbon is absorbed in the form of CO2 and converted to glucose which may then be used for respiration and building of protoplasm in plants. Plants are then consumed by primary consumers and the carbon is then transferred into the body tissues of animals. Through successive feeding, carbon compounds move up the trophic levels in the ecosystem.

Respiration:

Plants and animals respire, converting glucose into CO2, which is release back into the atmosphere.

Excretion and egestion:

Microorganisms ferment carbon-rich food in the stomachs of cattle and releases carbon back into the atmosphere in the form of natural gases or methane, CH4. Undigested food removed as faeces contains much of the carbon that was initially ingested as well.

Decomposition:

As dead organisms decay and become decomposed, they release carbon dioxide into the atmosphere.

Destruction of vegetation:

Bush fires or slash-and-burn agriculture may burn away large areas of forests which release large quantity of carbon dioxide from plant material

Sedimentation and mineralization:

When organisms die and are very quickly buried, they do not undergo decomposition, but may be compacted by layers of mud and rock. Overtime these dead organisms may become fossil fuels. Much of the carbon in the tissues of these organisms thus becomes stored in the formed of fossil fuels.

Carbon dioxide from the atmosphere dissolves in the sea in the form of bicarbonate ions or carbonate ions. Marine organisms use carbonate ions to produce hard shells and support structures. When these organisms die, their hard shells will settle down to the bottom of the ocean (sedimentation) and become compacted. This becomes limestone (calcium carbonate) over a long period of time, storing the carbon in limestone.

Dissolution:

Precipitation may dissolve limestone structures, thus releasing the carbonate ions back into rivers and streams.

Burning of Fossil Fuels (combustion):

When fossil fuels is removed from deep underground, and burnt for energy, the carbon in the fossil fuel is released as large quantities of carbon dioxide.

Nitrogen Cycle:

It helps to keeps the nitrogen level in the atmosphere constant and ensures a continuous supply of nitrates for green plants to make proteins and protoplasm. It also enables proteins to be supplied to other organisms in the food chains.

Nitrogen is removed from the air:

-By nitrogen-fixing bacteria to produce nitrates in the soil

-By lightning that combines nitrogen with oxygen in the air to form oxides of nitrogen. The oxides of nitrogen dissolve in water to from nitric acid. The nitric acid reacts with other substances to form nitrates.

Nitrogen is returned to the air:

-By the action of denitrifying bacteria on the nitrates found in the soil, decomposing the nitrates into oxygen for the bacteria’s use and nitrogen for release into the air.

Nitrogen compounds are removed from the soil:

-Through the absorption by green plants for their growth

-By leaching; in which nitrates dissolve in rain water or drainage water and are washed away beyond the reach of plant roots.

Nitrogen compounds are returned to the soil:

-By the action of decomposers on dead animals and plants