Chapter 5 - Natural Biogeochemical Cycles

The Carbon Cycle

• Carbon
  • Fundamental element of life.
  • Carbon is found in CO2, which makes up 1% of the atmosphere.
• Plant Matter
  • A portion of atmospheric carbon is removed through photosynthesis in which carbon gets incorporated into plant structures and compounds.
• Terrestrial Biosphere
  • Forests store 90% of the planet's aboveground carbon and 75% of soil carbon.
• Oceans
  • Carbon dissolved in seawater is used for phytoplankton and kelp for photosynthesis.
• Sedimentary Deposits
  • Limestone and carbon trapped in fossil fuels and coal.
• Every year, billions of tons of carbon are exchanged between the atmosphere, plants, soil, and the ocean.

Nitrogen Cycle

• Nitrogen makes up 78% of the atmosphere.
• Essential for amino acids, proteins, and nucleic acids.
• Nitrogen Fixation - Atmospheric nitrogen is converted into ammonia or nitrate ions which are biologically usable forms of nitrogen.
• Nitrification - Ammonia is converted into nitrate and nitrite.
• Assimilation - Plants absorb ammonia, ammonium ions, and nitrate ions through their roots.
• Denitrification - Anaerobic bacteria convert ammonia into nitrites, nitrogen gas, and nitrous oxide.
• Effects of excess nitrogen
  • Ammonia has tripled since the industrial revolution. It decreases air quality.

Sulfur Cycle

• Sulfur in the lithosphere
  • Sulfur in the lithosphere is mobilized by slow weathering of rock material.
• Sulfur in the hydrosphere
  • The main source of sulfur in the oceans is through dissolved sulfate.
• Sulfur in the Soil
  • Main sources come from deposition from the atmosphere, weathering of rocks, release from decay of organic matter and fertilizer, pesticides, and irrigation water.

The Water Cycle

• The water cycle is in a state of dynamic equilibrium by which the rate of evaporation equals the amount of precipitation.
• Processes of the water cycle include evaporation, evapotranspiration, condensation, infiltration, runoff, and precipitation.

Role of H2O, C, N, P, and S in the human body

• Water - Helps to dissolve minerals, makes them accessible to the body, regulates body temperature, and carries nutrients and oxygen to cells throughout the body.
• Carbon - Allows the building of long, complex chains of molecules.
• Nitrogen - Found in many organic molecules, including the amino acids that make up proteins and nucleic acids that make up DNA.
• Phosphorus - Found in the bone and in the molecule ATP.
• Sulfur - Found in 2 amino acids that are important for giving proteins their shape.

\