Download The Nitrogen cycle

The Nitrogen cycle
(p.52-65)
Why nitrogen?
 All
living things need nitrogen to live
 Nitrogen is an essential component
of proteins and DNA
Nitrogen Fixation
 Plants
(p.54-55)
need nitrogen, phosphorus
and potassium that we can find in
fertilizers.
 So it’s convenient that 80% of our
atmosphere in nitrogen gas!
 BUT… plants aren’t capable of
absorbing nitrogen directly from the
atmosphere.
 They need some help
Solution…
 In
soil and water there are
Nitrogen fixing bacteria.
 Many of these live on the roots of
beans, peas, clover and similar
plants
How?
 Nitrogen
is combined with hydrogen
and oxygen to form ammonia or
nitrates (NH4+) (NO3-).
 Before artificial fertilizers, farmers
planted peas, beans and clover to
make the earth fertile again.
The Nitrogen Cycle in a Terrestrial
ecosystem



1) Nitrogen is converted to ammonia by
Nitrogen fixing bacteria and to
nitrates by nitrifying bacteria.
2. a) Plants absorb the nitrate so it can
enter the food chain
2. b) OR the nitrate is transformed into
nitrogen gas by denitrifying bacteria.
This way, the nitrogen gets back into the
atmosphere.
If there’s too much nirtogen in
the soil
It degrades tree roots
 Needles yellow and fall. When they
decompose they make the soil more
acidic.
 Acidic soil can dissolve toxic metals
like aluminum
 Aluminum kills fungi that live on
roots and help trees absorb minerals.

In the atmosphere
 Burning
fossil fuels releases nitrogen
compounds into the atmosphere
 This
causes acid rain
Eutrophication
 Nitrogen
fertilizer runs off from
farms, gardens and lawns into the
water
 Causes
 Which
accelerated plant growth
uses all the oxygen and other
elements needed by the fish
In the oceans: Algal blooms
 Creates
huge mats of (sometimes
toxic) algae that can be seen from
space.
Things you need to remember
1- Plants and animals need nitrogen
2- They can’t use the nitrogen in the
atmosphere directly
3- We rely on nitrogen fixing, nitrifying
and denitrifying bacteria to convert back
and forth between the type we can use
(nitrate) and the type we can’t (nitrogen
gas)
It also helps to know…
4- These bacteria also convert the nitrogen
in excrement and decomposing things
5- Too much nitrogen in the wrong place
can cause:
-soil to become acidic
-acid rain
-eutrophication (lakes choked by
weeds)
-algal blooms in the ocean