1. Section 3.3 The Nitrogen and Phosphorus Cycles
Chapter 3
Section 3.3
The Nitrogen and Phosphorus Cycles

2. 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.

3. The Nitrogen Cycle Organic Nitrogen in Living Things
Nitrogen Gas in Atmosphere
Inorganic Nitrogen in Soil
Organic Nitrogen in Living Things
Inorganic Nitrogen in Soil
Nitrogen Gas in Atmosphere

4. Nitrogen Fixation
There are two ways in which atmospheric nitrogen can be converted to nitrates, in a process called nitrogen fixation.
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

5. 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.

6. 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:
Biological Cycle
Geochemical Cycle

7. 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.

8. 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.

9. 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.

10. 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.