The Nitrogen Cycle

1
The Nitrogen Cycle

• All organisms require nitrogen to make amino
  acids which are used to make proteins.
• Many different forms of nitrogen in the biosphere
• Organic nitrogen is continually recycled by
  plants and animals.
• Nitrogen-containing compounds act as nutrients in
  streams and rivers as well as in the soil.

2
A Atmosphere

• Nitrogen gas makes up 78-79 of Earth's
  atmosphere, but most organisms can not use
  nitrogen gas (N2).
• Nitrogen gas is not usable by plants or animals
  directly.

3
B Nitrogen Fixation (atmospheric)

• During electrical storms, nitrogen gas can be
  converted into NO3- (nitrate) during a process
  called atmospheric nitrogen fixation

4
C Legume Plants and Nitrogen Fixation

• Certain types of bacteria that live freely in the
  soil or within root nodules of legumes can
  convert the nitrogen gas into ammonia during the
  process called bacterial nitrogen fixation.

5
D Nitrogen Fixing Bacteria

• Found in soil AND on legume roots, they change
  the N2 (gas) to ammonia.

6
E Ammonification

• The conversion of nitrogen gas to ammonia (hence
  ammonification) is key to the fixation process.
• Some plants can use ammonia directly but most
  need nitrogen changed to nitrates through the
  next process.

7
F Nitrification

• Other types of bacteria that live in the soil
  change ammonia to nitrates.

8
G Nitrosomonas

• These bacteria start the nitrification process by
  converting ammonia to nitrites.

9
H Nitrobacter

• These bacteria finish the job by converting the
  nitrites to nitrates.

10
I Consumption by Plants

• Nitrates are taken up by autotrophs.

11
J Consumption by Animals

• Animals consume the autotrophs and therefore
  obtain their nitrogen needs.

12
K Denitrification

• Some soil bacteria take nitrates and convert it
  into N2, returning nitrogen gas back into the
  atmosphere.
• The breaking apart of the nitrates is where this
  term comes from.