Where exactly in the chloroplast does the light-dependent stage take place?

In the thylakoid membranes of the grana and in the thylakoid spaces they enclose.

What is a light harvesting complex?

A light harvesting complex is a cluster of pigment molecules held in the thylakoid membrane that absorbs light and funnels the energy to the reaction centre of a photosystem.

What happens to an electron in the reaction centre of a photosystem when light energy reaches it?

The electron absorbs the energy and is raised to a higher energy level, so that it leaves the chlorophyll molecule, which is called photoactivation.

Describe what happens to an excited electron once it has left a photosystem.

It is picked up by an electron acceptor and passed along a chain of electron carriers in the thylakoid membrane, releasing energy at each transfer.

OCR A-Level Biology B H422

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Photosynthesis, Food Production and Management of the Environment

The light-dependent stage of photosynthesis

3 things to know
Components 01, 02 and 03

Overview

Recall questions on where the light-dependent stage happens, light harvesting complexes and photoactivation, the electron transport chain and proton gradient, photophosphorylation by ATP synthase, the photolysis of water, NADP as final electron acceptor, and the effects of darkness and herbicides.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

Name the two products of the light-dependent stage that are passed on to the light-independent stage.

Key term

How is the energy released by the electron transport chain used to build a proton gradient?

Key term

Explain how ATP is generated once a proton gradient exists across the thylakoid membrane.

Questions from this subtopic

Each one with the model answer underneath.

1
Where exactly in the chloroplast does the light-dependent stage take place?
Model answer
In the thylakoid membranes of the grana and in the thylakoid spaces they enclose.
2
Name the two products of the light-dependent stage that are passed on to the light-independent stage.
Model answer
ATP and reduced NADP.
3
What is a light harvesting complex?
Model answer
A light harvesting complex is a cluster of pigment molecules held in the thylakoid membrane that absorbs light and funnels the energy to the reaction centre of a photosystem.
4
What happens to an electron in the reaction centre of a photosystem when light energy reaches it?
Model answer
The electron absorbs the energy and is raised to a higher energy level, so that it leaves the chlorophyll molecule, which is called photoactivation.
5
Describe what happens to an excited electron once it has left a photosystem.
Model answer
It is picked up by an electron acceptor and passed along a chain of electron carriers in the thylakoid membrane, releasing energy at each transfer.
6
How is the energy released by the electron transport chain used to build a proton gradient?
Model answer
The energy is used to pump protons from the stroma into the thylakoid space, so a high concentration of H⁺ builds up inside the thylakoid.

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