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Photosynthesis – Light Reaction

Photosynthesis – Light Reaction. Biology CP. Light Reaction. Light Reaction – in a nutshell. Occurs in the thylakoid membrane of the chloroplast. Is a series of steps that takes light, moves electrons along the membrane, and eventually makes the energy molecules – NADPH and ATP. Step 1.

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Photosynthesis – Light Reaction

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  1. Photosynthesis – Light Reaction Biology CP

  2. Light Reaction

  3. Light Reaction – in a nutshell • Occurs in the thylakoid membrane of the chloroplast. • Is a series of steps that takes light, moves electrons along the membrane, and eventually makes the energy molecules – NADPH and ATP.

  4. Step 1 • Sunlight (photons) hit a special protein on the membrane called “Photosystem 2” that contains chlorophyll a. • Also here - water is split into Hydrogen, electrons, and Oxygen (a waste product). • Electrons become “excited”, causing them to leave photosystem 2 and move along an “electron transport chain”.

  5. Light Reaction

  6. Step 2 • As electrons move along the chain, hydrogen ions build up inside the thylakoid. • The electrons reach another protein containing chlorophyll a called “Photosystem 1”.

  7. Light Reaction

  8. Step 3 • Electrons again are “excited” and move along to another electron transport chain. • These electrons reach the side of the membrane that is next to the stroma (fluid of the chloroplast). • Here they combine with H and NADP (the final electron acceptor) to make NADPH (an energy molecule).

  9. Light Reaction

  10. Making ATP • The hydrogen ions that have built up inside the thylakoid now can move through an enzyme called “ATP synthase”. • The movement of these hydrogen ions through the ATP synthase provides the energy needed to convert ADP to ATP.

  11. Light Reaction

  12. Final products of the light reaction • 1. NADPH (energy molecule) • 2. ATP (energy molecule) • 3. oxygen (waste product) • The energy molecules can then be used in the Calvin cycle (dark reaction)

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