The Nitrogen Cycle
Free Nitrogen exists in the air. It can NOT be used by humans in this form. Thus a
complex cycle of Nitrogen Fixation exists.
1. Free Nitrogen is “fixed” into a useable form (Nitrogen Compund)
by
.
2. Humans and other organisms eat the Nitrogen compound when we consume
.
3. Humans and other organisms excrete waste which contains Nitrogen Compound.
4.
break down the waste and also remains of organisms and return
Free Nitrogen into the soil.
5. Other
in the soil release Free Nitrogen back into the atmosphere.
6. What is the difference between the role of bacteria that exists in the root nodules of
some plants and the miscellaneous other bacteria in the soil?
The Nitrogen Cycle Continued
79% of the air around us is _____________ . Living things need nitrogen to make
proteins, but they cannot get it directly from the air because nitrogen gas is too stable to
react inside an organism to make new compounds.
So nitrogen must be changed into a more reactive form to allow plants and animals to
use it. Plants can take up and use nitrogen when it is in the form of _______________
or ammonium salts. Changing nitrogen into a more reactive substance is called
________________________.
Nitrogen fixation happens in three different ways:
1. The energy in a ____________________ can split the di-atomic nitrogen
molecule in the air allowing each nitrogen atom to react with oxygen to form
nitrogen oxides. These oxides are washed to the ground by the rain where they
form nitrates.
2. The _____________________ is used by industry to produce
_________________from nitrogen. Ammonia is used to make fertilizer for
farmers to feed their crops.
3. ____________________________ found in the soil and in the root nodules of
leguminous plants fix nitrogen into a usable form.
Nitrogen compounds are returned to the soil by _____________________and
____________________from animals or when plants and animals die and decay. The
nitrogen compounds returned in this way are changed back to nitrogen gas by
denitrifying bacteria which live in the soil - thus completing the cycle.