Download Nitrogen Cycle

Nitrogen Cycle
•
•
•
•
•
Nitrogen is essential to life – it is a component of protein used for growth and repair)
Nitrogen composes 80% of the atmosphere but it is not directly available in this form.
Plants get protein from the soil as nitrates
Animals get protein from plants / animals / bacteria
We depend on methods of replenishing the nitrates in the soil.
1.
Decomposition
dead organic matter is broken down by saprophytes (i.e.
bacteria / fungi) into ammonia or ammonia compounds
2.
Nitrification
Ammonia compounds are oxidised by nitrifying bacteria into
nitrites and then into nitrates.
3.
Nitrates
The active uptake of nitrates requires energy. The nitrates are
taken up by the root hair cell and are combined with
carbohydrates from photosynthesis into proteins
4.
Lightning
the high temperature of the flashes combine the oxygen and
nitrogen to form nitric or nitrous oxide gases. The gasses
dissolve in the moisture to form acid. These acids (nitric acids)
are washed into the soil with rain. They combine with other
chemicals in the soil forming ammonium compounds.
5.
Nitrates
The active uptake of nitrates requires energy. The nitrates are
taken up by the root hair cell and are combined with
carbohydrates from photosynthesis into proteins
6.
Symbiotic
bacteria
Symbiosis is the living together of two different species for their
mutual benefits.
7.
Leguminous
plants
These contain symbiotic bacteria on the end of their roots. These
bacteria trap the atmospheric nitrogen and convert it into
ammonium compounds in the soil. The plant gains nitrates (and
CO2) and the bacteria gains carbohydrates – mutual benefit!
8.
Addition of
manure /
compost
Increases nitrates in the soil. This is done by the cycle of
decomposition
9.
Factory made
fertiliser
This is readily soluble and so mineral ions are readily available
to the plant. Overuse destroys crumb structure of the soil. It also
increases the acidity and pollution.
10.
Denitrification
In water logged soil, there is no oxygen present. This means that
the roots cannot respire. The anaerobic bacteria flourish and use
the nitrates as a source of energy – releasing nitrogen gas into
the atmosphere – results in poor plant growth.
Nitrogen gas (N2)
in the atmosphere
food for animals
death
death
Nitrogen fixation: Can occur with
energy from lightning or can be
carried out by nitrogen fixing
bacteria (may live in plant roots)
decomposers – saprophytes (i.e. bacteria / fungi) convert
the dead organic matter to ammonium compounds
Nitrate ions absorbed
by plants by diffusion
and active transport
Ammonium compounds /
ammonia
Denitrification – removes the
nitrates in the soil. Carried out by
denitrifying bacteria – only
occurs in waterlogged conditions.
Nitrifying bacteria Nitrate ions (NO3 ) in soil
solution
(aerobic conditions)
Nitrification