Carbon Cycling

Carbon Cycling

1. 1. Carbon Fixation

   • Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds
   • Autotrophs absorb carbon dioxide from the atmosphere and convert it into: Carbohydrates, Lipids and other organic compounds
     • This reduces the carbon dioxide concentration in the atmosphere
     • The mean CO2 concentration is currently 0.039% in the atmosphere
       • This is different in areas with higher rates of photosynthesis

2. 2. Carbon Dioxide in Solution

   • In aquatic habitats carbon dioxide is present as a dissolved gas and hyrdogen carbonate ions
   • Carbon dioxide is soluble in water
     • It can remain as a dissolved gas or combine with water to form carbonic acid
     • It can dissociate to form hydrogen and hydrogen carbonate ions
       • Lowering the pH of the water
     • Both dissolved carbon dioxide and hydrogen carbonate ions are absorbed by aquatic plants and other autotrophs in water

3. 3. Absorption of Carbon Dioxde

   • Carbon dioxide diffuses from the atmosphere into autotrophs
     • Autotrophs use carbon dioxide in production of carbon compounds seen through photosynthesis
       • This reduces the CO2 concentration in autotrophs and sets up a concentration gradient
         • This gradient is between the cell and air or water surrounding it
   • Carbon dioxide diffuses from atmosphere or H2O into autotrophs
     • In land plants with leaves diffusion occurs through the stomata on the underside of the leaf
       • In aquatic plants the entire surface of leaves and stems are permeable to CO2
         • Diffusion can occur in any part of aquatic plants

4. 4. Release of Carbon Dioxide form Cellular Respiration

   • Carbon Dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere
   • Carbon Dioxide is a waste product of respiration (Aerobic)
     • It is produced in all cells that carry out respiration
       • This can be grouped by tropic levels: Animal cells, Non-photosynthetic cells in plants and Saprotrophs
       • Carbon dioxide produced by respiration diffuses out of cells and passes into the atmosphere or water surrounding the organism

5. 5. Methanogenesis

   • Methane is produced from organic matter in anaerobic conditions by methanogenic archaens
     • Some methane diffuses into the atmosphere
   • The volta collected bubbles of gas emerging from mud in a reed bed on the margins of lake maggiore Italy
     • The gas was inflammable
     • Volta had discovered methane but did not name it
     • It is produced in anaerobic environments, it is a waste product of a type of anaerobic respiration
       • 3 groups of anaerobic prokaryotes are involved
         • Bacteria that converts organic matter into a mixture of organic acids, alcohol, hydrogen and CO2
         • Bacteria that use the organic acids and alcohol to produce acetate, carbon dioxide and hydrogen
         • 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