Summary (Nutrient/Carbon Cycle)

Nutrient cycle

-       While the Earth receives a continuous input of solar energy from the Sun, the total amount of each of the elements on Earth remains relatively constant since the formative stages of our planet.

-       i.e. The Earth does not receive additional amount of carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur after it is formed.

-       Hence, as plants and animals grow and die, they cycle these elements between the environment and their bodies through various:

-       biological processes such as photosynthesis, cellular respiration anddecomposition.

-       And geological processes such as sedimentation.

-       And processes  arising from the action of human beings such as deforestation andburning of fossil fuel.

-       Living things on earth are primarily made up of the following elements:

-       Carbon

-       Hydrogen

-       Oxygen

-       Nitrogen

-       Phosphorus

-       Sulfur

-       They also require the following compound as the main solvent/medium in which biochemical processes take place within:

-       Water

Carbon Cycle

Carbon is found in all ecosystems, because all living things on Earth are composed of carbon compounds.

Just as the Sun is the main source of energy for an ecosystem, the atmosphere is the main source of carbon for all ecosystems (“main source” does not mean having the most amount of carbon stored. Carbon is only very readily obtained from the atmosphere).

Ensures continuous supply of carbon dioxide for plants to carry out photosynthesis enables energy to flow through the ecosystem

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

- Photosynthesis:

Carbon is absorbed in the form of CO2 and converted to glucose which may then be used for respiration and for the 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 released back into the atmosphere.

- Excretion and Egestion:

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

- 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 form of fossil fuel.

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 (Chemical weathering):

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

- Burning of fossil fuel (Combustion):

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