8.3 Photosynthesis (AHL) Flashcards
What are the two parts of photosynthesis?
Light dependent and light-independent reactions.
What are the products of the light-dependent reactions?
ATP and reduced NADP (NADPH)
Where do the light-dependent reactions occur?
Thylakoid space across the thylakoid membranes.
What is meant by photoactivation?
Where a photon’s energy is absorbed by an electron in a chlorophyll molecule and becomes excited
What is a photosystem? Which photosystem starts the light reactions?
- A group of chlorophyll and accessory pigments together in a light-harvesting array inside the thylakoids.
- Photosystem II.
What is plastoquinone?
- Hydrophobic electron acceptor for photosystem II.
- Collects two excited electrons from PII and then moves them away to another position in the membrane.
- Absorption of two photons causes the production of one reduced plastoquinone. This is repeated to produce two reduced plastoquinones.
Explain chemiosmosis in PII.
The protons travel back across the thylakoid membrane, down the concentration gradient, by passing through ATP synthase. The energy released by the passage of protons down their concentration gradient is used to make ATP from ADP and inorganic phosphate. This is called non-cyclic phosphorylation.
What happens in Photosystem I?
Electrons in the chlorophyll molecules within PI are photoactivated. The electrons then pass along a chain of electron carriers in PI, at the end of which it is passed to ferredoxin, a protein in the fluid outside the thylakoid. Two molecules of reduced ferredoxin are then used to reduce NADP, forming NADPH.
How are PI and PII linked?
The electrons that PI donated to the ETC is replaced by an electron carried by plastocyanin, which transfers the electron to PII.
What happens when the supply of NADP runs out?
Electrons return to the ETC that links PI and PII instead of being passed to NADP. As the electrons flow back to PI on the ETC, they cause the pumping of protons, which allow ATP production. This is called cyclic phosphorylation.
What two light-dependent reaction products are carried through to the light-independent reactions?
NADPH and ATP.
What is the name of the five-carbond compound present in the Calvin Cycle?
Rubisco
Define carboxylation.
Introduction of a carboxyl group to a compound or molecule.
What are the three stages of the Calvin Cycle?
Carbon fixation, reduction reactions, and the regeneration of rubisco.
What occurs in carbon fixation?
- Carbon dioxide in the stroma reacts with a 5C compound, RuBP, to form a six-carbon compound. This reaction is catalysed by an enzyme called rubisco.
- As soon as the six-carbon compound is formed, it splits to form two molecules of glycerate 3-phosphate.
