Cycles

Carbon Cycle

Processes involved in the carbon cycle are:

Photosynthesis – plants absorb CO2 from the atmosphere and convert it into organic compounds. This is the only process in the carbon cycle that decreases the level of atmospheric CO2.

Feeding – moves carbon in biological molecules along food chains.

Respiration – when living organisms (plants, animals and decomposers (bacteria and fungi)) respire they release CO2 into the atmosphere.

Fossilisation – in some conditions, dead organisms may not decay, Instead, they get compressed over millions of years and form fossil fuels (coal, oil or gas) or carbon stores such as limestone.

Weathering – acid rain can dissolve limestone, releasing CO2.

Combustion – when fossil fuels are burned, CO2 is released into the atmosphere.

Excretion – carbon compounds are excreted in urine. This material is then broken down by decomposers.

Egestion – carbon is egested in faeces. This material is then broken down by decomposers.

Decomposition – carbon compounds in dead organisms, urine and faeces are broken down by decomposers (bacteria or fungi).

Describe how the carbohydrates in the dead leaves of eucalypt trees would be recycled by the activity of detritivores and microorganisms.

  • Detritivores break leaves into small pieces / increase surface area
  • Deposit faeces
  • Increases rate of microbial action
  • Bacteria and fungi (microorganisms) decompose / break down leaves or organic matter
  • Secretion of enzymes for digestion
  • Absorption of sugars
  • Respiration by detritivores/ microorganisms
  • Release of carbon dioxide
  • Carbon dioxide used in photosynthesis.

Explain how the felling and burning of trees on a large scale could affect the concentration of carbon dioxide in the atmosphere.

  • Burning releases carbon dioxide
  • Less carbon dioxide removed by trees/less removed in photosynthesis.
Carbon Cycle Transfers

•Carbon is transferred between reservoirs without changing form.

•Carbon dioxide (CO₂) is transferred from the atmosphere into plant leaves through diffusion via stomata.

•CO₂ is also transferred between the atmosphere and oceans through simple diffusion.

•Feeding transfers unchanged organic molecules from plants to animals and then to predators.

•Movement of dead organic matter transfers carbon into soil, and sedimentation transfers carbonates into ocean sediments.

•Human activities such as cutting forests transfer organic carbon from vegetation into the soil and atmosphere.

Carbon Cycle Transformations

•Carbon is transformed when chemical reactions change its form.

•Photosynthesis transforms CO₂ and water into glucose (C₆H₁₂O₆) and oxygen:

  6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

•Respiration transforms glucose back into CO₂ and water:

  C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.

•Decomposition transforms complex organic molecules into simpler carbon compounds and CO₂.

•Geological processes transform dissolved carbon into calcium carbonate (CaCO₃) in shells and rock.

•Combustion transforms stored carbon from fuels or biomass into CO₂ and water vapour.