The Nitrogen Cycle:
 The transfer of nitrogen from the atmosphere to the soil, to living organisms,
and back into the atmosphere is called the Nitrogen cycle.
 Living things cannot exist without nitrogen. It is a basic element of all living
things. (It is essential for cells & DNA)
 Nitrogen is found in both living and
nonliving things.
 Atoms of nitrogen don’t just stay in one
place. They move slowly between living
things, dead things, the air, soil, and
water.
 Most of the nitrogen on Earth is in the
atmosphere. But, most organisms cannot
use nitrogen directly from the air.
 The molecules of nitrogen can become
usable to living things when they are
broken apart during lightening strikes,
volcanic activity, fires, or certain bacteria.
-Plants absorb nitrogen compounds through their roots.
-Animals obtain nitrogen by eating plants or other animals.
-When organisms die, the nitrogen in their bodies returns to the soil or
atmosphere.
The Nitrogen Cycle:
The transfer of __________________ from the
atmosphere
to
the
soil,
to
__________________________________, and
back into the atmosphere is called the nitrogen
cycle.
 Nitrogen is important to all __________________ things.
 Nitrogen is a essential for ______________ and _______________.
 Most of the nitrogen is found in the ______________________, but
organisms cannot use nitrogen directly from the air.
 Nitrogen does not always stay in __________ place. They move between
_____________ things, ______________ things, the ________, and water.
Plants absorb these nitrogen compounds through their roots.
Animals obtain nitrogen by eating plants or other animals.
When organisms die, the nitrogen in their bodies returns to the soil or
atmosphere.
Humans affect the nitrogen cycle.
Farming depletes the nitrogen compounds in the soil.
If the nitrogen compounds are not replaced, the soil will become
infertile.
Nitrogen is a limiting factor for plant growth.
Have you ever noticed that adding fertilizers to the soil can make your
plants grow greener, fuller, and healthier? Fertilizers contain nitrogen
compounds.
Composts (Remember back to our discussion on compost piles) and animal
manure contain needed nitrogen compounds.
Farmers also plant nitrogen – fixing crops.
Nitrogen – fixing bacteria live on the or in the roots of some plants
(such as
peas and beans)
The molecules of nitrogen in the atmosphere can become usable for living things when:
1. They are broken apart during lightning strikes or fires
2. Dead and decaying matter gets broken down by bacteria (decomposer) and then is available
in the soil to living organisms
3. When certain types of bacteria that live on plant roots supply nitrogen compounds to the
plant