Download Phosphorus and Nitrogen Cycle

Chapter 3
Section 3.3
The Nitrogen and Phosphorus
Cycles
The Nitrogen Cycle
• Nitrogen atoms are required so that cells can make
proteins.
• They are also required to make DNA, the hereditary
material found in all living things.
• The Nitrogen Cycle – is a cycle of matter in which
nitrogen atoms move from nitrogen gas in the
atmosphere, to inorganic forms in the soil, to organic
forms in living things, and then back to inorganic forms in
the soil and nitrogen gas in the atmosphere.
The Nitrogen Cycle
Nitrogen Gas in
Atmosphere
Inorganic
Nitrogen in Soil
Organic Nitrogen in Living Things
Inorganic
Nitrogen in Soil
Nitrogen Gas
in Atmosphere
Nitrogen Fixation
•
There are two ways in which atmospheric nitrogen can
be converted to nitrates, in a process called nitrogen
fixation.
1.
-
Lightning
The energy from lightning causes nitrogen gas to react
with oxygen to form nitrates
The nitrates dissolve in rain or surface water, enter the
soil and then into plants
-
2. Bacteria in the Soil
- Some bacteria in the soil are also capable of converting
nitrogen gas into nitrate usable in plants
Nitrogen and Decomposers
• Decomposers break down the nitrogen containing
materials chemicals in the waste or body into simpler
compounds such as ammonia (NH3).
• Then other decomposers break these down into nitrites
and then other convert these into nitrates usable by
plants.
• Sometimes during the decay process, nitrites will be
converted back into nitrogen gas by a process called
denitrification.
• Denitrification – the process in which nitrates are
converted to nitrites and then to nitrogen gas.
The Phosphorus Cycle
•
Phosphorus is a key element in cell
membranes, in molecules that release
chemical energy, in the making of DNA, and in
the calcium phosphate of bones.
•
The Phosphorus Cycle in the cycling of
phosphorus between the biotic and abiotic
components of the environment.
• The cycle consists of 2 parts:
1. Biological Cycle
2. Geochemical Cycle
Geochemical Cycle
• This long term cycle involves the rocks of
Earth’s crust.
• Phosphorus is found in bedrock in the
form of phosphate ions (PO43-).
• The phosphates dissolve in the water of
rivers and soils. The rivers contribute to
run-off to the ocean.
Geochemical Cycle
• Eventually the phosphates will be used by
organisms and then deposited when they
die.
• The deposits eventually become rock,
which is ready to be brought to the surface
again.
• The process can take millions of years to
complete.
Biological Cycle
• The phosphates that are dissolved in
rivers and soils can also be picked up by
plants and pass into the food chain.
• When these organisms die, decomposers
break down the phosphates and they enter
the soil once again to be swept off into the
ocean or enter the food chain.
Variations in Nutrient Cycling
• Nitrogen and Phosphorus are both nutrients.
• Nutrients as chemicals that are essential to living beings.
• The cycling of nutrients is directly related to the rate of
decomposition.
• The faster the decomposition and the faster the cycling
of nutrients.
• Ex. The rainforest is very warm and moist so
decomposition occurs very quickly, therefore the cycling
of nutrients is also faster.