AQA Biol4: Photosynthesis

Revision notes on photosynthesis including the light dependent and light independent reactions from AQA Biol4

  • Created by: anna
  • Created on: 14-06-13 15:41

The Light-Dependent Reaction/Photophosphorylation

  • Takes place in the thylakoid membranes in the chloroplast
  • Light energy is absorbed and excites electrons in the chlorophyll
  • The electrons move to a higher energy level and move along the electron transport chain
  • As the electrons move along the electron transport chain they must be replaced
  • Light energy splits water into protons, electrons and oxygen
  • Electrons lose energy as they move along the transport chain , this energy is used to transport protons into the thylakoid forming a proton concentration gradient across the membrane
  • Protons move down the concentration gradient into the stroma via ATP synthase to form ATP
  • More light energy is absorbed exciting electrons to an even higher energy level
  • The electrons are transferred to NADP with a proton to form NADPH
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The Light-Independent Reaction/Calvin Cycle

  • Takes place in the stroma of the chloroplasts
  • Carbon dioxide is combined with ribulose bisphosphate (RuBP) a 5 C compound making an unstable 6 C compound (the enzyme rubisco catalysess this)
  • This quickly breaks down into a 3 C compound called glycerate 3-phosphate (GP)
  • ATP from the light dependent reaction provides energy to turn glycerate 3-phosphate into a 3 C compound triose phosphate (TP)
  • This reaction also uses NADPH from the light dependent reaction
  • 5 out of 6 triose phosphate molecules are used to regenerate RuBP
  • 1 out of 6 TP molecules is used to make organic substances such as glucose
  • The cycle has to turn 6 times to make one hexose sugar
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