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Biology Revision notes:
The Carbon and Nitrogen Cycles
Photosynthesis and respiration are the exact opposite of each other, and because both processes
take place, Carbon Dioxide and Oxygen are continually recycled and balanced.
Decomposers and nutrients:
In all ecosystems, dead organisms and waste material are broken down by bacteria and fungi called
decomposers. This process is called decay or decomposition and releases nutrients back into the soil.
Decomposition must take place in a moist, aerobic environment (containing H2O and O2).
Living organisms die and are decomposed by decomposers, ending up in the soil
Plant takes in minerals
Plants are eaten by animals (sheep etc.) and minerals are taken in
Animals die and are decomposed
The minerals are passed back into the soil and the cycle restarts
Each time, 10% of the minerals are passed on.
The Carbon Cycle:
Carbon never leaves the atmosphere, it is just converted into different forms, therefore there
always has been, and always will be the same amount of carbon in the Earth's ecosphere (excluding
waste into space).
Carbon is found naturally in the atmosphere (in Carbon Dioxide etc.), the only way to get it
out of the atmosphere is through photosynthesis.
Photosynthesis in plants uses carbon dioxide to make glucose, which is then eaten by animals
Some of this carbon is immediately respired back into the atmosphere, but more remains in
the bodies of the animals.
When animals die and decay, more CO2 is given off into the atmosphere are decomposers
break down the body.
If animals die, but aren't decayed (not in right conditions etc.), over millions of years, they
are trapped as sediments(fossilisation and sedimentation) and then in fossil fuels
The combustion (burning) of fossil fuels releases Carbon into the atmosphere
When volcanoes erupt, more carbon from sediments is released into the atmosphere.
The Nitrogen Cycle;
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Atmospheric Nitrogen is present as N2 in the atmosphere.
During storms, lightning converts nitrogen into nitrogen oxide, which dissolves in rain and
forms nitrates in the soil (NO3)2- (Nitrogen and Oxygen).
The nitrates in the soil are absorbed (active transport) into plants to make proteins are other
Plants are eaten by animals and the nitrogen is passed on
The animal then dies and is decayed in the soil.
Nitrifying Bacteria convert the ammonia from dead biomass (and from urea) into nitrates.…read more