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Biogeochemical cycles

These involve the linked biochemical and physical processes that move elements that are
important to living organism.

Living organisms are made of many elements. Hydrogen, oxygen, carbon, nitrogen, sulphur
and phosphorus are especially important, but many others are also needed. For some of
these, there are not enough…

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Carbon is the basis of life because it is the only element that can form long chains of atoms
and therefore produce a huge variety of different compounds, in combination with
elements such as hydrogen, oxygen, nitrogen, sulphur and phosphorus.

The most readily accessible reservoir of carbon is carbon dioxide,…

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Photosynthesis captures light energy using pigments such as chlorophyll. It
converts low-energy substances such as carbon dioxide and water into high-energy
carbohydrates that can be stored for later use. Oxygen is a by-product.
Respiration releases the energy from high-energy substances such as
carbohydrates that can be used to drive metabolic…

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Anaerobic gut bacteria in the intestines of livestock release methane into the atmosphere,
which may be subsequently oxidised to carbon dioxide.

Anaerobic bacteria in rice paddy fields release methane.

Soil disturbances by ploughing increase the rate of decomposition, which release more
carbon dioxide into the atmosphere.

Global climate change increases…

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Ionising phenomena are the events that provide the energy for atmospheric nitrogen and
oxygen to react and produce oxides of nitrogen, such as lightning and forest fires. The
oxides of nitrogen can dissolve in rainwater and produce dilute nitric acid. When this is
washed into the soil it will react…

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the amount of nitrates washed into the soil by rain.

The Phosphorus cycle

Phosphorus is an important component of bones, proteins, ATP, DNA and RNA.

The phosphorus cycle is very different from the carbon and nitrogen cycles in that the
atmosphere is not involved. Phosphorus compounds, usually as phosphates, are…

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are not usually leached from fields because of their low solubility but they are present in


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