AQA Biol4: Photosynthesis

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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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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