Chapter 5 - Photosynthesis

  • Created by: stef17
  • Created on: 27-04-16 14:41
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  • Chapter 5 - Photosynthesis
    • 6CO2 + 6H2O --> C6H12O6 + 6O2
    • Light dependent stage
      • Photophosphorylation
        • Cyclic
          • Only PSI
          • Only makes ATP
        • Photosystems
          • Photosystem I is the second one
          • Photosystem II is the first one
        • Non-cyclic
          • Z scheme
          • Uses both photosystems
          • produces NADPH and ATP
    • Light independent stage
      • Also known as the Calvin cycle
        • 1. CO2 is combined with RuBP using the enzyme rubisco
        • 2. This forms a six-carbon intermediate
        • 3. This splits to form two glycerate-3- phosphate (GP) molecules
        • 5/6ths GP used to regenerate RuBP
        • 1/6th used to make sugars
        • 4. This is used to form six triose phosphate (TP) molecules
    • Photosynthetic pigments
      • Main pigments are chlorophyll a and b
      • Accessory pigments and carotenoids and xanthophylls
    • Factors affecting the rate of photosynthesis
      • CO2 concentration
        • If a plant has more CO2, it can photosynthesise faster due to the Calvin cycle working faster. Howeer, if there is not enough CO2 then both GP and TP levels fall, RuBP levels fall in some plants too
      • Light intensity
        • Calvin cycle
          • GP levels rise and TP levels fall
        • Light dependent stage
          • Give a plant more light, and it can photosynthesise faster, due to more energy eing ale to 'excite' electrons, until light is no longer a limiting factor
      • Temperature
        • Photosynthesis happens faster at higher temperatures but only up to a point. Photosynthesis is an enzyme-catalysed reaction so above certain temperatures the enzymes stop working properly. At high temperatures, rubisco starts catalysing the combination of RuBP and oxygen - instead of CO2, this is called photorespiration


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