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Nitrogen
cycle
Joanna
George-Johnson, Contributor
The
nitrogen cycle is one of the least
popular topics among students. It
is, however, a necessary topic in
the study of biology. For this lesson
I will break it down into simple steps
for you.
Nitrogen
is a very important element for all
living things. No proteins would be
produced if there were no nitrogen.
In
this cycle, free atmospheric nitrogen
(N2) is converted into soluble nitrogen
compounds, then incorporated into
plants and animals, and then returned
to the atmosphere through organic
decomposition.
When
plant proteins are eaten by animals,
the nitrogen is removed as amino acids
and used to build animal protein.
The
amount of nitrogen available in the
atmosphere is always the same, so
it has to be cycled.
To
study the nitrogen cycle we will break
it down into two sections:
1.
The incorporation of nitrogen into
the living world
2.
The release of nitrogen into the atmosphere
The
incorporation of nitrogen into the
living world
Because
the triple bond of molecular nitrogen,
(N=N), is so strong, most living things
cannot use it directly. Atmospheric
nitrogen must first be converted into
a usable form so plants can incorporate
them into their structure. The process
by which this is done is called fixation.
(Actually, the term 'fixation' applies
to any gaseous substance that is condensed
into a more usable form.)
The
fixation of nitrogen can occur in
three ways:
biologically,
atmospherically,
Industrially.
Most
natural nitrogen fixation occurs when
atmospheric nitrogen is converted
to ammonia compounds by soil bacteria
such as Rhizobium.
This
process occurs on the roots of leguminous
plants such as peas and beans.
The
next step in nitrogen fixation is
called 'nitrification' and occurs
when other bacteria converts ammonia
compounds into nitrites (NO2-) and
nitrates (NO3-).
This
enriches the soil for plants, which
use soluble nitrates to form plant
proteins.
When
these plant proteins are eaten by
animals, the nitrogen is removed as
amino acids and used to build animal
protein.
Bacteria
breaks down amino acids from dead
plants and animal waste products (urine
and faeces) and releases ammonia compounds.
Nitrogen
fixation also occurs atmospherically,
when lightning forms oxides of nitrogen
and is washed into the soil.
The
release of nitrogen into the atmosphere
The
nitrogen cycle is completed when anaerobic
bacteria (denitrifying) breaks down
nitrates and other nitrogen compounds
in the soil to release free nitrogen
back into the atmosphere.
Therefore,
each step of the cycle is mainly dependent
on the use of micro-organisms.
Questions
1.
Construct a table showing the micro-organisms
involved in the nitrogen cycle, outlining
their function.
2.
What is the purpose of nitrogen fixation?
Nitrogen
Cycle
Joanna
George-Johnson teaches at Ardenne
High School.
Email: Masterbio@gmail.com.
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