Here are the steps of the light reaction of photosynthesis arranged in the correct order:
- Photosystem II receives photons in the form of light energy.
- Light energy is transferred to a chlorophyll reaction center where electrons become energized.
- Electrons from the reaction center become energized and escape Photosystem II, moving down the electron transport chain.
- A protein in the electron transport chain pumps H+ ions from the stroma into the thylakoid space.
- Water is split to replace the electrons lost in Photosystem II.
- Electrons move down the electron transport chain, releasing energy.
- Electrons from the electron transport chain replace the electrons lost in Photosystem I.
- Electrons from Photosystem I become energized and move down a second electron transport chain.
- At the end of the electron transport chain, the energized electrons and H+ ions are used to reduce NADP+ to NADPH.
- H+ ions flow down their concentration gradient through ATP synthase, releasing energy in the process.
- ATP synthase uses energy to add a phosphate group to ADP, forming ATP.
This sequence highlights the key events in the light-dependent reactions of photosynthesis that take place in the thylakoid membranes of chloroplasts.