VI. Cycles in the Environment

A. Carbon Cycle

1. Cycles the organic matter necessary for all life

2. Bulk is preformed by life through photosynthesis and respiration

a. 6CO2 + 6H2O + Energy C6H12O6 + 6O2

b. Most carbon is locked in life because of this

3. As death and sedimentation occur, atmospheric carbon gets trapped as rock and fossil fuels.

4. Oceans also absorb CO2 from the air and volcanic eruptions

a. This can combine with Ca to form CaCO3 which makes shells of aquatic life

5. CO2’s atmospheric concentration is increasing

a. Burning of fossil fuels

b. Loss of plants that cycle

c. There is an undiscovered sink though

B. Phosphorus Cycle

1. Key to production of membranes, DNA, RNA, and ATP

2. Very small amount present in life and negligible in the atmosphere

3. Vast majority locked in rock sand released slowly by weathering

a. Dissolves in water which can:

1. precipitate back out to form rocks

2. be absorbed by plants and incorporated into the food web

a. This is the limiting element in plant growth

4. Because amount limits growth, it is a main component of fertilizers

a. Excess runs off, removing limitation from plants and algae

1. these overgrow, using up resources such as oxygen killing themselves and other organisms

C. Nitrogen Cycle

1. N2 makes up 78% of atmosphere but is inaccessible to most life.2. Must be made biologically active by nitrogen fixation3. Several steps

a. Specially adapted nitrogen-fixing bacteria combine it with H2 to make ammonia (NH3)

1. live in the root nodules of legumes

b. Ionized by water, NH4+ (ammonium) can be used by few plants

c. Other bacteria use nitrification to convert ammonium in to more readily usable NO2- (nitrite) and NO3- (nitrate)

1. also what is in fertilizers

d. Plants then pass N up the food web

e. Process can also by-pass N fixing bacteria as lightning can produce

ammonia as well

4. As organisms decay, bacteria release N2 back into air to start over

5. Along with phosphates, nitrates in fertilizers have created dead spots in several waterways.