The Light-dependent reaction

Photoionisation

When light hits the chlorophyl molecule causing the electrons to get excited and be released from the molecule. The molecule becomes positive, therefore oxidised.

electron carrier

Where the electrons ae taken up. It becomes reduced.

Where are the electron carriers?

Where are the redox reactions also happening?

Thylakoid membrane.

What is some of the energy from the high-energy electrons used to make?

Used to combine ADP with Pi to make ATP.

What is the name of the mechanism in which ATP is produced.

chemiosmotic theory

Briefly describe the chemiosmotic theory: 4

• H+ ions (protons) are pumped into the thylakoid from the stroma, using protein carriers in the thylakoid membrane called proton pumps.

• The energy to drive this process is from the photolysis of water.

• Photolysis of water also produces protons, increasing their concentration in the thylakoid space. This creates a concentration gradient of the protons in the thylakoid and in the stroma.

• The protons can only cross the thylakoid membrane through the ATP synthase channel proteins. They pass through these channels, which cause changes to the structure of the enzyme ATP synthase which catalyses the combination of ADP with Pi to form ATP.

Equation for the photolysis of water

2 H20 → 4H+ + 4e- + O2

Where are the protons taken up?

What does this do to the molecule?

• Protons are taken up by the electron carrier NADP.

• On taking up the protons, NADP becomes reduced.

What is the main product of the light-dependent reaction?

reduced NADP and the electrons from the chlorophyll molecules.

Why is reduced NADP important?

It is a further potential source of chemical energy to the plant.

What is the by-product oxygen used for?

• Respiration

• Diffuses out of the the stoma.

Adaptations of chloroplasts that allow them to capture light for photosynthesis: 3

• Thylakoid membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the light- dependent reaction.

• Granal membraned have ATP synthase channels within them, which catalyse the production of ATP.

• Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in the light-dependent reaction.