Briefly describe the Z-scheme and why is it called so?
GeneralClass 12AllAnswered 27 Mar 2026
Answer
The Z-Scheme describes non-cyclic electron flow:
Why "Z-shaped"?
When electron carriers are arranged on a redox potential scale (vertical axis) and sequence of transfer (horizontal axis), the path resembles the letter "Z".
Electron flow sequence:
- PS II (P680) → excited electrons to high energy level
- Downhill through electron transport chain → releases energy for ATP synthesis
- PS I (P700) → electrons re-energized
- Downhill again to NADP⁺ → forms NADPH
Key features:
- Two photosystems working in series
- Two light-dependent boosts (creating the "Z" peaks)
- Water donates electrons at beginning (bottom left)
- NADPH forms at end (bottom right)
- ATP synthesis occurs during downhill electron flow
Redox potential range: +0.8 V (H₂O/O₂) to -0.6 V (NADP⁺/NADPH)
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