The Electron Transport (Z-scheme)
The sequential movement of electrons from PSII to PSI via various electron carriers, forming the Z-scheme of electron flow.
What is The Electron Transport (Z-scheme)?
A diagrammatic representation of the electron flow during the light-dependent reactions of photosynthesis, showing the sequential excitation and transfer of electrons from water to NADP+ through Photosystem II and Photosystem I.
Key formula / rule: Water Splitting (Photolysis)
Key points
- Describe the path of electrons in the Z-scheme.
- Identify the roles of PSII and PSI in electron transport.
- Explain the generation of ATP and NADPH during non-cyclic photophosphorylation.
- Understand the significance of water splitting and oxygen evolution.
Common exam trap
Confusing the order of electron flow between PSII and PSI.
Definitions
- Term
Z-scheme
- Meaning
A diagrammatic representation of the electron flow during the light-dependent reactions of photosynthesis, showing the sequential excitation and transfer of electrons from water to NADP+ through Photosystem II and Photosystem I.
- Term
Non-cyclic photophosphorylation
- Meaning
The process where light energy is used to produce ATP and NADPH, involving the linear flow of electrons from water to NADP+ through both photosystems, with oxygen as a byproduct.
- Term
Plastoquinone (Pq)
- Meaning
A mobile electron carrier in the thylakoid membrane that accepts electrons from PSII and transfers them to the cytochrome b6f complex.
- Term
Cytochrome b6f complex
- Meaning
A protein complex in the thylakoid membrane that transfers electrons from plastoquinone to plastocyanin and pumps protons into the thylakoid lumen.
- Term
Plastocyanin (Pc)
- Meaning
A mobile electron carrier that transfers electrons from the cytochrome b6f complex to Photosystem I.
- Term
Ferredoxin (Fd)
- Meaning
An iron-sulfur protein that accepts electrons from Photosystem I and transfers them to NADP+ reductase.
Learning objectives
Describe the path of electrons in the Z-scheme.
Identify the roles of PSII and PSI in electron transport.
Explain the generation of ATP and NADPH during non-cyclic photophosphorylation.
Understand the significance of water splitting and oxygen evolution.
List the key electron carriers involved in the Z-scheme.
Formulae
- Name
Water Splitting (Photolysis)
- Note
Occurs at Photosystem II (PSII).
- Expression
2H₂O → 4H⁺ + 4e⁻ + O₂
Prerequisites
Structure of chloroplasts
Photosynthetic pigments (Chlorophylls, Carotenoids)
Light-dependent reactions of photosynthesis
Photosystems I and II
Common mistakes
Confusing the order of electron flow between PSII and PSI.
Forgetting that water splitting occurs at PSII.
Not understanding the role of the proton gradient in ATP synthesis.
Confusing cyclic and non-cyclic photophosphorylation.
Misidentifying the electron carriers.
Keywords
Z-scheme
Non-cyclic photophosphorylation
Photosystem II
Photosystem I
Electron Transport Chain
ATP synthesis
NADPH production
Water splitting
Thylakoid membrane
Plastoquinone
Cytochrome b6f
Plastocyanin
Ferredoxin
P680
P700
Photolysis
Chemiosmosis
Practice preview
The photolysis of water, which provides electrons for the Z-scheme, occurs in association with which photosystem?…
easy
Which of the following are the main products of non-cyclic photophosphorylation?…
easy
The electron transport pathway in non-cyclic photophosphorylation is termed the 'Z-scheme' primarily due to which characteristic?…
medium