Carbon Cycling

Carbon Cycling

1. Carbon Fixation
1. Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds
2. Autotrophs absorb carbon dioxide from the atmosphere and convert it into: Carbohydrates, Lipids and other organic compounds
  1. This reduces the carbon dioxide concentration in the atmosphere
  2. The mean CO2 concentration is currently 0.039% in the atmosphere
    1. This is different in areas with higher rates of photosynthesis
2. Carbon Dioxide in Solution
1. In aquatic habitats carbon dioxide is present as a dissolved gas and hyrdogen carbonate ions
2. Carbon dioxide is soluble in water
  1. It can remain as a dissolved gas or combine with water to form carbonic acid
  2. It can dissociate to form hydrogen and hydrogen carbonate ions
    1. Lowering the pH of the water
  3. Both dissolved carbon dioxide and hydrogen carbonate ions are absorbed by aquatic plants and other autotrophs in water
3. Absorption of Carbon Dioxde
1. Carbon dioxide diffuses from the atmosphere into autotrophs
  1. Autotrophs use carbon dioxide in production of carbon compounds seen through photosynthesis
    1. This reduces the CO2 concentration in autotrophs and sets up a concentration gradient
      1. This gradient is between the cell and air or water surrounding it
2. Carbon dioxide diffuses from atmosphere or H2O into autotrophs
  1. In land plants with leaves diffusion occurs through the stomata on the underside of the leaf
    1. In aquatic plants the entire surface of leaves and stems are permeable to CO2
      1. Diffusion can occur in any part of aquatic plants
4. Release of Carbon Dioxide form Cellular Respiration
1. Carbon Dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere
2. Carbon Dioxide is a waste product of respiration (Aerobic)
  1. It is produced in all cells that carry out respiration
    1. This can be grouped by tropic levels: Animal cells, Non-photosynthetic cells in plants and Saprotrophs
    2. Carbon dioxide produced by respiration diffuses out of cells and passes into the atmosphere or water surrounding the organism
5. Methanogenesis
1. Methane is produced from organic matter in anaerobic conditions by methanogenic archaens
  1. Some methane diffuses into the atmosphere
2. The volta collected bubbles of gas emerging from mud in a reed bed on the margins of lake maggiore Italy
  1. The gas was inflammable
  2. Volta had discovered methane but did not name it
  3. It is produced in anaerobic environments, it is a waste product of a type of anaerobic respiration
    1. 3 groups of anaerobic prokaryotes are involved
      1. Bacteria that converts organic matter into a mixture of organic acids, alcohol, hydrogen and CO2
      2. Bacteria that use the organic acids and alcohol to produce acetate, carbon dioxide and hydrogen
      3. Archaens that produce methane from carbon dioxide, hydrogen and acetate by 2 chemical reactions
        CO2 + 4H2----> CH4 +2H2O
        CH3COOH---->CH4+CO2
        Carry out methanogenesis in anaerobic environments including: Mud along river beds, Swamps, guts of dead animal matter etc
        Some of the methane is diffused into the atmosphere thus it cannot escape and is burned as fuel

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