Download Humans and the Carbon Cycle

Humans and the Carbon Cycle
– Respiration releases __________ into the air.
– Burning fossil fuels releases CO2 into the
atmosphere.
– Burning of wood and natural forest fires also
release CO2 into the atmosphere.
– Half of this CO2 remains in the atmosphere,
which may contribute to global warming.
– The rest dissolves into the ocean or is absorbed
by plants.
The Nitrogen Cycle
The Nitrogen Cycle
• Nitrogen:
– is needed to build proteins.
– makes up 78% of the atmospheric gases.
– cannot be used straight out of the atmosphere by
most organisms; it must be “fixed” first.
• Nitrogen-fixing bacteria:
– can “fix” atmospheric nitrogen into chemical
compounds.
– live in soil and in nodules on some plant roots.
– release “fixed” nitrogen into the soil, where it is
used by other plants.
The Nitrogen Cycle (cont.)
How is nitrogen in the atmosphere changed
into a form that can be used by
organisms?
1. Nitrogen-fixing bacteria:
a) Take atmospheric nitrogen and “fix” it into
useable compounds (ammonia).
b) Release “fixed” nitrogen into the soil.
2. Lightning converts some nitrogen into
useable nitrates.
The Nitrogen Cycle (cont.)
4. Some soil bacteria convert ammonia into
nitrates.
5. Bacteria (in soil AND water) change a small
amount of the nitrogen back into
atmospheric nitrogen.
6. Decomposers release nitrogen from
organisms back into the soil.
• So where does MOST of the nitrogen stay in
the cycle?