Question

Consider these events of photosynthesis.

1. Light energy excites electrons.
2. Water molecules are split.
3. NADPH is formed.

In which locations do each of these events occur?

Responses

1. photosystem I
2. photosystem I
3. photosystem II
1. photosystem I 2. photosystem I 3. photosystem II

1. photosystem II
2. photosystem II
3. photosystem I
1. photosystem II 2. photosystem II 3. photosystem I

1. photosystem I
2. photosystem II
3. photosystem II
1. photosystem I 2. photosystem II 3. photosystem II

1. photosystem II
2. photosystem I
3. photosystem I

Answer 1

Correct choice: 1 = photosystem II, 2 = photosystem II, 3 = photosystem I.

Brief explanation:
- Light excites electrons in the pigment reaction centers of both photosystems, but the initial excitation in the linear electron flow is at PSII (P680).
- Water splitting (oxygen-evolving complex) happens at PSII.
- NADPH is formed at the end of the chain when electrons from PSI (P700) are used by ferredoxin–NADP+ reductase to reduce NADP+ to NADPH.