photosynthesis Flashcards
Where do the light-dependent & light-independent reactions occur in plants?
Light-dependent - in the thylakoids of chloroplasts.
Light-independent - stroma of chloroplasts.
Explain the role of light in photoionisation.
Chlorophyll molecules absorb energy from photons of light.
This ‘excites’ 2 electrons (raises them to a higher energy level), causing them to be released from the chlorophyll.
Name the 2 main stages involved in ATP production in the light-dependent reaction.
- electron transfer chain.
- chemiosmosis.
What happens in the electron transfer chain (ETC)?
Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane & undergo a series of redox reactions, which releases energy.
How is a proton concentration gradient established during chemiosmosis?
Some energy released from the ETC is coupled to the active transport of H+ ions (protons) from the stroma into the thylakoid space.
How does chemiosmosis produce ATP in the light-dependent stage?
H+ ions (protons) move down their concentration gradient from the thylakoid space into the stroma via the channel protein ATP synthase.
ATP synthase catalyses ADP + Pi - ATP.
Explain the role of light in photolysis.
Light energy splits molecules of water.
2H2O - 4H+ + 4e- + O2
What happens to the products of the photolysis of water?
H+ ions: move out of thylakoid space via ATP synthase & are used to reduce the coenzyme NADP.
e- : replace electrons lost from chlorophyll.
O2: used for respiration or diffuses out of leaf as waste gas.
How and where is reduced NADP produced in the light-dependent reaction?
NADP + 2H+ + 2e- - reduced NADP.
Catalysed by dehydrogenase enzymes.
Stroma of chloroplasts.
Where do the H+ ions and electrons used to reduce NADP come from?
H+ ions: photolysis of water.
Electrons: NADP acts as the final electron acceptor of the electron transfer chain.
Name the three main stages in the Calvin cycle.
- Carbon fixation.
- Reduction.
- Regeneration.
What happens during carbon fixation.
Reaction between CO2 and ribulose bisphosphate (RuBP) catalysed by rubisco.
Forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP).
What happens during reduction (in the Calvin cycle)?
2x GP are reduced to 2x triose phosphate (TP).
Requires 2x reduced NADP & 2x ATP.
Forms 2x NADP & 2x ADP.
How does the light-independent reaction result in the production of useful organic substances?
1C leaves the cycle (i.e. some of the TP is converted into useful organic molecules).
What happens during regeneration (in the Calvin cycle)?
After 1C leaves the cycle, the 5C compound RuP forms.
RuBP is regenerated from RuP using 1x ATP.
Forms 1x ADP.
