Photosynthesis – Light Reaction - PowerPoint PPT Presentation

Photosynthesis – Light Reaction

Biology CP

• 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.

• 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”.

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

• 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).

• 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.

• 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)