18.104.22.168 Aerobic: break down organic compounds
to carbon dioxide, releases more energy.
22.214.171.124 Anaerobic: allows some organisms to survive and use food
sources in oxygen-deficient environments, releasing methane.
1.1.3 Food chains
126.96.36.199 Pass organic compounds between organisms.
188.8.131.52 Incomplete decomposition of organisms under anaerobic conditions, leads
to deposition of fossil fuels. Some marine organisms absorb carbon dioxide
and store it in their skeletons, later form sediments of limestone and chalk.
184.108.40.206 Release carbon dioxide from fossil fuels or carbonate rocks.
1.2 Dynamic equilibria
1.2.1 Inputs and outputs balance. A change in the cycle results in negative
feedback mechanisms, rebalance the cycle allow the planet to remain stable.
1.2.2 Global homeostatis
220.127.116.11 Natural negative feedback mechanisms combine to
produce a self-regulating system resisting change.
18.104.22.168 Gaia hypothesis: considers Earth as single interacting system made
up of biotic and abiotic parts maintaining stability. Some consider it
as a single organism. Impact of human activities disguised by
feedback mechanisms that counteract them, humans may cause
changes that stop feedback (deforestation) or cause changes that
are too rapid for feedback mechanisms to act quick enough.
1.3.2 Coal mines, gas and oil processing release methane.
1.3.3 Combustion of wood reduces stored carbon, increases atmospheric
carbon dioxide. Reduced photosynthesis and fixation of carbon in biomass.
1.3.4 Anaerobic gut bacteria release methane, subsequently oxidised to carbon dioxide.
1.3.5 Anaerobic bacteria in rice padi fields release methane.
1.3.6 Soil disturbance by ploughing increases rate of decomposition, more carbon dioxide.
1.3.7 Global climate change increases rate of decomposition, releasing more carbon
dioxide. Increases rate of photosynthesis, absorbing more carbon dioxide. Methane
released from melting permafrost or methane hydrate in marine sediments.
1.4 Basis of life, forms long life chains of atoms
producing a large variety of compounds.
2 Phosphorus cycle
2.1 Important component
in DNA, RNA, ATP,
bones and proteins.
2.2 Atmosphere not involved, phosphates not soluable, limiting
factor on plant growth (particularly in oceans where there
are no rocks to release phosphates during weathering.)
2.3 Dissolved phosphates are absorbed by plants, passed along food chains. Phosphates
excreted or found in dead organic matter may be available for other plants or be lost to
sediments. Humans increase crop growth y manufacturing soluable phosphate
fertilisers from phosphate rocks. Causes eutrophication if leached from fields because
of their low solubility but are present in sewage effluent.
3 Nitrogen cycle
3.1 Essential component of proteins (enzymes, cell
membranes, hormones), DNA, RNA and chlorophyll.
3.2 Most immobile in rocks or in the atmosphere,
no plants or animals can assimilate it directly
or reuse nitrogenous wastes they release.
3.3.1 Ionising phenomena
22.214.171.124 Provide energy for atmospheric nitrogen and oxygen to react and
produce oxides of nitrogen (lightning, forest fires.) Oxides of
nitrogen can dissolve in rainwater and produce dilute nitric acid,
when washed into soil it reacts with minerals in soil to form nitrates.
3.3.2 Reduction of nitrogen to ammonia
126.96.36.199 Carried out by micro-organisms during nitrogen fixation, some live
freely in soil others symbiotically in root nodules of leguminous plants.
3.3.3 Food chains
188.8.131.52 Pass nitrogen between organisms as amino acids and proteins.
184.108.40.206 Oxidation of ammonium ions to nitrites then to nitrates by nitrifying bacteria.
220.127.116.11 Chemical reduction of nitrates in soil to nitrogen and nitrogen oxide gases by anaerobic denitrifying bacteria, released into atmosphere.
18.104.22.168 Loss of soluable substances such as nitrates from surface layers of soil, carried away by water.
3.3.7 Absorption of soluable ions of nitrates, nitrites and ammonium from the soil by roots.
3.4 Human impacts
3.4.1 Haber process involves industrial fixation of atmospheric nitrogen by converting it to ammonia with large amounts of energy.
3.4.2 Nitrate fertilisers may increase problems of leaching (particularly if followed by rain.)