LIGHT ENERGY EXCITES THE ELECTRONS IN CHLOROPHYLL
- Light energy is absorbed by Photosystem II
- The light excites the electrons in chlorophyll, and these electrons move to a higher energy level.
- The high energy electrons move along the electron transport chain to Photosystem I
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PHOTOLYSIS OF WATER PRODUCES PROTONS (H+ ions), EL
- As the excited electrons from the chlorophyll leave photosystem II to move along the electron transport chain, they have to be replaced.
- Water is split into oxygen, protons and electrons by light (this is called photolysis).
H2O----->2H+ and 1/2 O2
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ENERGY FROM THE EXCITED ELECTRONS MAKES ATP
- The excited electrons lose energy as they move along the electron transport chain.
- Protons are transported into the thykaloid membranes by using the energy from the excited electrons. This means that the thykaloid membrane has a higher concentration of protons than the stroma, and a proton concentration gradient is formed.
- Protons move down the concentration gradient, and into the stroma; via ATP synthase (an enzyme)
- ATP is formed from this energy from the combination of ADP and an inorganic phosphate.
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REDUCED NADP IS GENERATED
- Light energy is absorbed by photosystem I
- This excites the electrons to a higher energy level
- The electrons are transferred to NADP along with a proton (from the stroma)
- This forms reduced NADP
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- Only uses photosystem I
- Electrons from the chorophyll molecule aren't passed onto NADP but are passed back to photosystem I via electron carriers (hence cyclic)
- The electrons are recycled
- No NADP or O2 are produced; only small amounts of ATP
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