Edexcel A-Level Biology A 9BN0
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Photosynthesis: the light-dependent reactions
- 3 things to know
- Papers 1 and 3
Overview
Recall questions on the excitation of chlorophyll, photophosphorylation, reduced NADP and photolysis, how their products drive the light-independent reactions, and isolating chloroplasts and measuring the Hill reaction with DCPIP.
What you need to know
Answer each one before you reveal it.
Explain why the light-independent reactions cannot continue indefinitely without light.
What happens to electrons in chlorophyll when light energy is absorbed during the light-dependent reactions?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What happens to electrons in chlorophyll when light energy is absorbed during the light-dependent reactions?
Model answer
The electrons become excited (raised to a higher energy level) by the absorbed light energy.
- 2
How are excited electrons from chlorophyll used to produce ATP?
Model answer
The excited electrons pass through electron carriers, and the energy released is used to generate ATP in a process called photophosphorylation.
- 3
What molecule is formed when excited electrons from chlorophyll are used to reduce NADP?
Model answer
Reduced NADP (NADPH).
- 4
What process produces oxygen during the light-dependent reactions?
Model answer
Photolysis of water.
- 5
Besides oxygen, what other products are released by the photolysis of water?
Model answer
Electrons and protons (H⁺ ions), which are used in the light-dependent reactions.
- 6
What is the role of the products from the light-dependent reactions in the light-independent reactions?
Model answer
ATP and reduced NADP from the light-dependent reactions are used to reduce carbon dioxide in the light-independent reactions.
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