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Questions and Answers

What is the primary function of the electron transport chain in the light reactions of photosynthesis?

To synthesise NADPH

To catalyse the reduction of CO2

To produce ATP through chemiosmosis (correct)

To regulate the activity of Rubisco

What is the name of the enzyme that catalyses the first reaction in the Calvin cycle?

Ribulose bisphosphate carboxylase

Rubisco (correct)

Ribulose bisphosphate oxygenase

Carbonic anhydrase

In which part of the chloroplast do the light-dependent reactions take place?

Thylakoid membrane (correct)

Stroma

Lamella

Grana

What is the primary function of the photosystems in the light-dependent reactions?

To reduce NADP+ to NADPH Signup and view all the answers

What is the term for the process by which C3 plants can overcome the problem of photorespiration?

Keeping gas exchange pores open Signup and view all the answers

What is the term for the process by which some plants have specialized anatomies to separate CO2 fixation from the Calvin cycle?

C4 pathway Signup and view all the answers

What is the function of the water splitting complex in PSII?

To replace the lost electron in P680 Signup and view all the answers

What is the role of the electron transport chain in thylakoid membrane?

To synthesize ATP Signup and view all the answers

What is the function of the cytochrome complex in the electron transport chain?

To pump protons from the stroma to thylakoid space Signup and view all the answers

What is the role of chloroplast ATP synthase?

To produce ATP Signup and view all the answers

What is the function of P700 in PSI?

To receive light energy from antennae chlorophylls Signup and view all the answers

What is the function of the reaction centre in PSI?

To pass light energy to P700 Signup and view all the answers

What is the byproduct of the electron transport chain in PSI?

ATP and NADPH Signup and view all the answers

What is the function of plastocyanin in the electron transport chain?

To transfer electrons along the electron transport chain Signup and view all the answers

What is the primary function of the light reactions in photosynthesis?

To generate ATP and NADPH Signup and view all the answers

What is the role of the reaction centre chlorophyll in photosystem I?

To transfer electrons to the primary electron acceptor Signup and view all the answers

What is the function of the water-splitting complex in photosystem II?

To split water into oxygen and hydrogen ions Signup and view all the answers

What is the purpose of the electron flow in the light reactions?

To transfer energy from light to the Calvin cycle Signup and view all the answers

What is the role of plastocyanin in the light reactions?

To transfer electrons to the cytochrome complex Signup and view all the answers

What is the function of ATP synthase in the light reactions?

To synthesize ATP from ADP and Pi Signup and view all the answers

What is the purpose of the antennae chlorophylls in photosystem II?

To absorb light energy and transfer it to the reaction centre Signup and view all the answers

What is the relationship between the light reactions and the Calvin cycle?

The light reactions produce ATP and NADPH, which are used in the Calvin cycle Signup and view all the answers

Study Notes

Photosynthesis

Photosynthesis is a form of energy transformation where electrons are removed from an electron donor (water in green plants) and transferred to NADP+ (giving NADPH).
The NADPH passes electrons onto CO2, which becomes reduced and forms sugars.

Light Reactions

Light reactions involve two types of photosystems: Photosystem I and Photosystem II.
Reaction centre chlorophylls are positioned close to primary electron acceptors in large protein complexes called photosystems.
Energy transduction or transformation: Light energy into chemical energy (reducing power).

Photosystem Components

Photosystem II:
- Reaction centre: P680
- Antennae: Chlorophyll, light-harvesting complexes
- Water-splitting complex
Photosystem I:
- Reaction centre: P700
- Antennae: Chlorophyll, light-harvesting complexes

Electron Flow and Energetics

Light energy is passed to reaction centre chlorophyll (P680 or P700) by antennae chlorophylls.
Excited electrons move from primary electron acceptors to electron transport chain (Plastoquinone, Cytochrome complex, Plastocyanin) in thylakoid membrane.
Electron transport chain creates a proton gradient, which is used by chloroplast ATP synthase to produce ATP.

Electron Transport Chain

Components: Plastoquinone, Cytochrome complex, Plastocyanin
Energy from electron transport chain is used to pump protons from stroma to thylakoid space.
Proton gradient is used by chloroplast ATP synthase to produce ATP.

Light-Independent Reactions (Calvin Cycle)

CO2 fixation, reduction into sugar, and recycling phase
First reaction is catalyzed by Ribulose bisphosphosphate carboxylase/oxygenase (Rubisco)
C3 plants can overcome photorespiration by keeping gas exchange pores open, while C4 and CAM plants have specialized anatomies/biochemistry for spatial or temporal separation of initial CO2 fixation.

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