NOTES: UNIT 4

Biogeochemical Cycles:
The process by which abiotic materials move from the atmosphere or soil into organisms and back again.

The Water Cycle:

• There are about 1.5 billion km³ of water on Earth.
  
• 97% of the water on earth is in the oceans.
• Only 3% of the water on earth is freshwater.
• Of this 3%, about 2.4% of the water on earth is permanently frozen in glaciers and the polar ice caps.
• About ¹/₂ of 1 % of the water on earth is groundwater.
• Only about ¹/₁₀₀ of 1% of the water on earth is in the rivers and lakes.

• Most cycling occurs through:
  
• Evaporation
• Transpiration
• Precipitation
• Condensation

http://ga.water.usgs.gov/edu/watercyclesummary.html

The Nitrogen Cycle:

This cycle converts atmospheric nitrogen, N₂ , into a form plants and animals can use.

Nitrogen makes up about 78% of the atmosphere. However, most living things cannot use atmospheric nitrogen and must rely on nitrates (NO₃^-) and nitrites (NO₂^-) in the soil.

Steps of the nitrogen cycle:

1. Nitrogen fixation - nitrogen-fixing bacteria, primarily living on the roots of legumes, convert nitrogen gas into NH₄OH.

2. Ammonification - bacteria decomposers break down amino acids from dead animals and animal wastes into NH₄OH.

3. Nitrification - chemosynthetic bacteria oxidize NH₄OH to produce nitrates and nitrites. The energy of lightning also causes atmospheric oxygen and nitrogen to combine to form nitrate ions.

Denitrification - anaerobic bacteria break down nitrates, releasing N₂ back into the atmosphere

This is a slow process requiring a lot of energy. Because of this, lack of nitrogen in the soil often limits the productivity of an ecosystem.

Your body must have nitrogen to make what compounds?

http://helios.bto.ed.ac.uk/bto/microbes/nitrogen.htm

http://www.physicalgeography.net/fundamentals/9s.html

The Carbon-oxygen cycle:

• Photosynthesis removes CO₂ from the air and adds O₂.
• Cellular respiration removes O₂ from the air and adds CO₂.
• Photosynthesis and respiration usually balance out.
• Decomposers break down organic material releasing CO₂.
• Increased levels of CO₂ in the atmosphere trap more heat and increase the possibility of global warming.

What is the cause of the increase in the amount of CO₂ in the Earth's atmosphere?

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CarbonCycle.html

http://www.physicalgeography.net/fundamentals/9r.html