NCP Step One:
- Light energy is absorbed by electrons in PSII.
- Light energy excites electrons in chlorophyll.
- The electrons move to a higher energy level, i.e they have more energy.
- The high energy electrons movealong the electron transport chain to PSI.
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NCP Step Two:
- The excited electrons from PSII must be replaced.
- Light energy splits a water molecule (photolysis) into protons (H+ ions), electrons and O2. This is where the O2 in photosynthesis comes from.
- The reaction is H2O -------> 2H+ + 1/2O2
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NCP Step Three:
- The excited electrons lose energy as they move along the electron transport chain.
- This energy is used to transport protons INTO the thylakoid membrane so that the thylakoid has a higher concentration than the stroma.
- This forms a proton concentration gradient (pH gradient) across the membrane.
- Protons move down their concentration gradient through an enzyme known as ATP synthase. (CHEMIOSMOSIS)
- The proton motive force causes the ATP synthase to rotate, and the active site to become accessable.
- ADP and inorganic phosphate (P) are then combined to make ATP.
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NCP Step Four:
- Light energy is absorbed by PSI, which excites the electrons to a higher energy level.
- The electrons are transferred to NADP along with a proton from the stroma (moved during chemiosmosis) to form reduced NADP (NADPH)
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- Only uses PSI.
- Electrons from chlorophyll do not reduce NADP but return to the photosystem via electron carriers.
- Electrons are recycled and flow repeatedly through PSI.
- Does not produce NADPH or O2.
- Produces ATP.
- Used in guard cells to open/close stomata.
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- The making of ATP from ADP and Pi, in the presence of light.
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- Molecules that transfer electrons.
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- Chemicals that accept electrons from another compound. They are reduced while acting as an oxidising agent.
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