Photosynthesis

  • Created by: Kayliss71
  • Created on: 23-05-18 20:40
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  • Photosynthesis
    • The light dependent reaction
      • Takes place in the thylakoid membranes of chloroplasts
      • Light is absorbed by chlorophyll in the photosystems
      • This energy excites electrons in chlorophyll leading to their eventual release from the molecule - chlorophyll has been photoionised
      • Some of the energy from the released electrons is used to resynthesise ATP and some is used to form reduced NADP. ATP transfers energy and reduced NADP transfers hydrogen to the light independent reaction
      • During the process H2O is oxidised to O2                  (Photolysis)
    • The light independent reaction
      • 1) Carbon dioxide is combined with ribulose bisphosphate (RuBP),  by the rubisco enzyme, to form an unstable 6 carbon molecule which is broken down into  two molecules of glycerate-3-phosphate (GP)
      • 2) ATP and reduced NADP are required for the reduction of GP to triose phosphate. Some of the triose phosphate is converted into useful organic compounds and some continues to regenerate RuBP
      • 3) Ribulose bisphosphate is regenerated by using up the remaining ATP from the light dependent reaction
      • Known as the Calvin cycle
      • Must occur 6 times to produce one hexose sugar
    • Limiting factors
      • Light intesnsity
        • Only certain wavelengths of light are used.
        • Photosynthetic pigments; chlorophyll a, b and carotene only absorb red and blue light.
        • Green light is reflected hence why leaves appear as green in colour
      • Temperature
        • Optimum is around 25 degrees
        • Any higher or lower then enzymes can denature
        • At high temperatures stomata begin to close to prevent water loss
      • Carbon dioxide
        • Stomata start to close if the concentration is above 0.4% - so less is taken in and can be converted to glucose
        • Concentration is around 0.04% in atmosphere, higher conc is better

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