Phosphorus Cycle

A SOIL-BASED VIEW OF THE PHOSPHORUS CYCLE
Initially, phosphate weathers from rocks. The small losses in a terrestrial system caused by leaching through the action of rain are balanced in the gains from weathering rocks. In soil, phosphate is absorbed on clay surfaces and onganic matter particles and becomes incorporated (immobilized). Plants dissolve ionized forms of phosphate. Herbivores obtain phosphorus by eating plants, and carnivores by eating herbivores. Herbivores and carnivores excrete phosphorus as a waste product in urine and feces. Phosphorus is released back to the soil when plants or animal matter decomposes and the cycle repeats.





A GLOBAL VIEW OF THE PHOSPHORUS CYCLE
The phosphorus cycle occurs when phosphorus moves from land to sediments in the seas and then back to land again. The main storage for phosphorus is in the earths crust. On land phosphorus is usually found in the form of phosphates. By the process of weathering and erosion phosphates enter rivers and streams that transport them to the ocean. Once in the ocean the phosphorus accumulates on continental shelves in the form of insoluble deposits. After millions of years, the crustal plates rise from the sea floor and expose the phosphates on land. After more time, weathering will release them from rock and the cycle's geochemical phase begins again.






AN ECOSYSTEM VIEW OF THE PHOSPHORUS CYCLE
The ecosystem phase of the phosphorus cycle moves faster than the sediment phase. All organisms require phosphorus for synthesizing phospholopids, NADPH, ATP, nucleic acids, and other compounds. Plants absorb phosphorus very quickly, and then herbivores get phosphorus by eat plants. Then carnivours get phosphorus by eating herbivores. Eventully both of these organisms will excrete phosphorus as a waste. This decomposition will release phosphorus into the soil. Plants absorb the phosphorus from the soil and they recycle it within the ecosystem.

Nitrogen Cycle

QUESTIONS:

1. The atmosphere is 80% nitrogen: why do you think plants and animals can't use 

    nitrogen as it is found in the atmosphere?

2. Explain what is meant by nitrogen fixation.

3. What is the role of bacteria in the nitrogen cycle?

4. Why don't legumes need nitrogen-containing fertilizers?

5. Why is nitrogen so important for living things?

6. What are the processes involved in the nitrogen cycle?

ANSWERS:

1. Plants and animals cannot use nitogen as it is found in the atmosphere as the nitrogen is in a form not usable to organisms. Plants and animals do not have the enzymes to 'fix' the nitrogen.

2. Nitrogen fixation is a process by which nitrogen (N₂) in the atmosphere is converted into ammonia (NH₃).^[1] Atmospheric nitrogen or elemental nitrogen (N₂) is relatively inert: it does not easily react with other chemicals to form new compounds. Fixation processes free up the nitrogen atoms from their diatomic form (N₂) to be used in other ways.

3. Bacteria actually uses and transforms the nitrogen into nitrogen that can again be used .

4. Legumes "fix" nitrogen in nodules on their roots, so they do not need additional nitrogen-containing fertilizers.

5. Nitrogen is a major component of chlorophyll, which is used by plants in the process of photosynthesis to produce sugars, water and carbon dioxide. 

It is also an essential component of amino acids which make up proteins. Some proteins act as structural units in the plant while others act as enzymes, catalysing biological reactions.

Nitrogen is also a component of ATP, which provides energy for reactions such as respiration.

Finally, nitrogen is a significant component of DNA, the genetic material which allows cells to grow and replicate.

6. Step 1: Nitrogen-fixation 
Atmospheric: Happens when Nitrogen (N2) is oxidized at high temperatures (by lightning, in internal combustion engines) to make nitrite (NO2). This can combine with water to form nitric acid (H2NO3), which is deposited on earth through rainfall. 
Biological: Done by bacteria which can convert N2 into ammonia (NH3) if an energy source is present. Some get this energy by directly absorbing sunlight (blue-green algae) or by living in the roots of plants (legumes, alder trees), who provide them with food (Rhizobium, Azospirillium). 
Step 2: Conversion to Ammonia. As amino acids and nucleic acids require N in the form of Ammonia, if nitrate (NO3) present, it must be converted to NH3. This is done through Nitrate reductase enzymes. 
Step 3: Biological Use. Ammonia is incorporated into proteins, nucleic acids 
Step 4: When organism dies, ammonia is relased back into the biosphere through the process of Ammonification, in which water is added to proteins to make carbon dioxide and ammonia. This process happens during digestion, and is also done by bacterial and fungal decomposers. 
Step 5: If ammonia released into oxygen rich (anerobic) soil, other bacteria can convert it into nitrite or nitrate through the process of Nitrification:

NH4+ + 2O2 = NO3- + H2O + 2H.

This is a problem, as it gives the molecule which contains Nitrogen a negative charge, which repels it from soil particles, causing it to be easily leached into streams and groundwater. 
Step 6: If soils remain anerobic, another group of poop will convert it back into inert, atmospheric N2 through the process of Denitrification. In this process, bacteria use nitrate as an Oxygen source for respiration: C6H12O6 + 4NO3- = 6CO2 + 6H2O + 2N2.

Vertical Structure of the Atmosphere

Discussion Questions

• Why are the four major layers of the atmosphere separated where they are?
• What increases the temperature in the stratosphere?
• Can planes fly in the mesosphere? Why or why not?
• On what does the temperature in the thermosphere depend?

Answers:

• Because it depends on their characteristics and their temperature.
• Ozone absorbs more ultraviolet radiation than does air in the troposphere. As a result, the stratosphere is heated, and air gradually increases in temperature to the top of the layer, called the stratopause.
• No; for two reasons:

         - There is insufficient oxygen present for an aircraft engine to work.
         - The atmospheric pressure is too low for an aircraft wing to obtain lift.

• It depends on air/ atmospheric pressure.