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Questions and Answers
What is the primary purpose of photolysis of water in the light-dependent reactions?
What is the primary purpose of photolysis of water in the light-dependent reactions?
Which process occurs in the thylakoid membranes during the light-dependent reactions?
Which process occurs in the thylakoid membranes during the light-dependent reactions?
What is produced during cyclic photophosphorylation?
What is produced during cyclic photophosphorylation?
What role do protons (H⁺) play in the light-dependent reactions?
What role do protons (H⁺) play in the light-dependent reactions?
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What is the end product of the light-dependent reactions that is essential for the Calvin cycle?
What is the end product of the light-dependent reactions that is essential for the Calvin cycle?
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Study Notes
Light-Dependent Reactions
- Location: Thylakoid membranes of chloroplasts
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Photolysis of Water: Water is split into oxygen, protons, and electrons.
- Equation: 2H₂O → 4H⁺ + 4e⁻ + O₂
- Provides electrons to replace those lost by chlorophyll
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Photosystem II (PSII):
- Light energy excites electrons in chlorophyll.
- Excited electrons move along the electron transport chain (ETC) to Photosystem I (PSI).
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Electron Transport Chain (ETC):
- Electrons pass through protein complexes in the thylakoid membrane.
- Energy released during this transfer pumps protons from the stroma into the thylakoid space.
- Creates a proton gradient
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Photosystem I (PSI):
- Light energy re-excites electrons in chlorophyll.
- Excited electrons are transferred to NADP⁺, along with protons from the stroma, to form reduced NADP (NADPH).
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Chemiosmosis and ATP Synthesis:
- The proton gradient drives ATP synthesis via ATP synthase.
- Protons flow back into the stroma through ATP synthase, providing energy to convert ADP + Pi into ATP
- This process is called photophosphorylation.
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End Products:
- ATP and NADPH are produced and used in the light-independent reaction (Calvin cycle).
- Oxygen is released as a by-product.
Key Processes
- Non-cyclic Photophosphorylation: Involves both PSII and PSI, producing ATP, NADPH, and oxygen.
- Cyclic Photophosphorylation: Involves only PSI, producing ATP but no NADPH or oxygen.
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Description
Test your understanding of the light-dependent reactions of photosynthesis. This quiz covers the processes occurring in the thylakoid membranes, including photolysis of water, electron transport, and ATP synthesis. Dive into the details of Photosystems I and II and the overall significance of these reactions.
