Download 4.3 Nitrogen cycle - Lighthouse Christian Academy

(Sec 4.3 pg 92 – 95)
CRASH COURSE VIDEO:
watch only the first half
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Even though nitrogen (N) is the most abundant gas
in the atmosphere, organisms cannot use it in
atmospheric form (N2).
N2 is very stable and will not break down.
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N is an essential component of biological molecules
(DNA, proteins, etc).
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For this reason, the N cycle is extremely important.
There are 3 key stages in the cycle (please refer to
Fig.2 p.93 and your Data Pages for diagrams of the N
cycle):
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Nitrogen fixation:
 Nitrogen gas (N2) is combined with hydrogen (H2) to form
ammonia (NH3).
 the process of N fixation is carried out by bacteria, many of
these bacteria live in the soil, others live on the nodules of
plants called legumes (Fig 3 p.93).
 Extra NH3 dissolves in the soil to become NH4+, ammonium
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Nitrification:
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Turns ammonium NH4+ into NO3- (nitrate ions); nitrate is
required by many plants for optimal growth.
process done by bacteria in the soil; the process is called
nitrification.
Nitrate ions are absorbed by plants to make amino acids,
DNA, proteins, etc.
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Decomposition and Denitrification:
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When organisms die, nitrates and ammonium leave the
body. It is converted back into N2 gas by decomposing
bacteria (this is called denitrification).
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Animals obtain their N by consuming plants, or by
consuming organisms that have consumed plants;
plants are essential for providing N to the food chain!