Light Dependent Reaction

Question 1

Oxidation?

Answer 1

Oxidation:

• Addition of oxygen
• Loss of electrons
• Loss of hydrogen
• Energy given out

Question 2

Chlorophyll and other pigments?

Answer 2

• Chloroplasts contain chlorophyll a+b and other pigment molecules such as carotenoids.
• The pigments absorb photons of light with different wavelengths.
• Different species of plants have different combinations of pigments giving different coloured leaves.

Question 3

Photosystems?

Answer 3

• The pigments are found in the thylakoid membranes attached to proteins.
• The protein and pigment are called a photosystem.

Question 4

What is light used for?

Answer 4

• To add an inorganic phosphate (Pi) molecule to ADP therefore making ATP.
• To split water into H+ ions (protons) and OH-. This is called photolysis.
• Making reduced NADP from NADP (gain of hydrogen).

Question 5

What is in a thylakoid membrane?

Answer 5

• Two kinds of photosystem (PS1 AND PS2) made up of 200 chlorophyll molecules and 50 molecules of accessory pigments.
• ATP synthase enzymes.
• Special molecules that transport electrons between each other and transports protons across the membrane.

Question 6

Reduction?

Answer 6

Reduction:

• Loss of oxygen
• Gains electrons
• Gains hydrogen
• Energy taken in

Question 7

Stage One?

Answer 7

1) Chlorophyll in PSII absorb photons of light which excites the electrons and gives it a higher energy.
2) The electrons move to an electron accepter protein molecule.
3) This causes the splitting (photolysis) of water: 2H2O → O2 + 4H+ + 4e-.
4) The oxygen produced diffuses out of the chloroplast and into the air.
5) The protons are released into the thylakoid lumen.
6) The electrons replace the excited electrons that have been ejected from the chlorophyll.

Question 8

Stage Two?

Answer 8

1) Excited electrons pass along electron transport chain in the thylakoid membrane.
2) Energy in electrons is used to pump protons from the stoma to the thylakoid lumen. This creates a proton gradient.
3) In PSI, more light energy is absorbed giving the electrons more excitation.

Question 9

Stage Three?

Answer 9

1) The electrons combine with some of the protons to form hydrogen atoms.
2) These are taken up by NADP which reduces it to NADPH: NADP + H+ + e- → NADPH
3) The NADPH moves to the stroma to be used up for the light-independent reaction.

Question 10

Stage Four?

Answer 10

1) The remaining protons diffuse down their gradient through the ATP synthase enzyme, producing ATP: ADP + Pi → ATP. This is called photophosphorylation.

Question 11

How are they adapted?

Answer 11

• Thylakoid membrane has a large surface area.
• Network of proteins in the grana hold chlorophyll which allows it to absorb maximum light.
• Granal membranes have enzyme attached which helps to manufacture ATP.
• Chloroplasts contain both DNA and ribosomes so they can quickly manufacture the proteins needed.