3.5.1 Photosynthesis Flashcards
(Photosynthesis) Where do the light-dependent & light-independent reactions occur in plants?
Light-dependent: in the thylakoids of chloroplasts.
Light-independent: stroma of the chloroplasts.
(Photosynthesis) Explain the role of light in photoionisation.
Chlorophyll molecules absorb energy form photons of light.
This ‘excites’ 2 electron a (raise a them to a higher energy level), causing them to be released from the chlorophyll.
(Photosynthesis) Name the 2 main stages involved in ATP production in the light-dependent reaction.
1) Electron transfer chain
2) Chemiosmosis
(Photosynthesis) 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.
(Photosynthesis) 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.
(Photosynthesis) 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 synthases catalyses ADP + Pi ➡️ ATP.
(Photosynthesis) Explain the role of light photolysis.
Light energy splits molecules of water.
2H2O ➡️ 4H+ + 4e- + O2
(Photosynthesis) What happens to the 3 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.
(Photosynthesis) How and where is reduced NADP produced in the light-dependent reaction?
- NADP + 2H+ + 2e- ➡️ reduced NADP
- Catalyses by dehydrogenase enzymes
- Stroma of chloroplasts
(Photosynthesis) 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
(Photosynthesis) name the 3 main stages in the Calvin cycle.
1) Carbon fixation
2) Reduction
3) Regeneration
(Photosynthesis) What happens during carbon fixation?
Reaction between CO2 and RuBP catalysed by rubisco.
Forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP).
(Photosynthesis) What happens during reduction (in the Calvin cycle)?
2x GP are reduced to 2x Triose phosphate
Requires 2x reduced NADP & 2x ATP
Forms 2x NADP & 2x ADP
(Photosynthesis) How does the light-independent reaction result in the production of useful organic substances?
1C leaves the cycle (I.e. some of the Triose phosphate is converted into useful organic molecules).
(Photosynthesis) 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.
(Photosynthesis) State the roles of ATP & (reduced) NADP in the light-independent reaction.
ATP: reduction of GP to Triose phosphate & provides phosphate group to convert RuP into RuBP.
(Reduced) NADP: coenzyme transports electrons needed for reduction of GP to Triose phosphate.
(Photosynthesis) State the number of carbon atoms in RuBP, GP & Triose phosphate.
RuBP: 5
GP: 3
Triose phosphate: 3
(Photosynthesis) Describe the structure of a chloroplast. (5)
1) Usually disc-shaped.
2) Double membrane (envelope).
3) Thylakoids: flattened discs stack to form grana.
4) Intergranal lamellae: tubular extensions attach thylakoids in adjacent grana.
5) Fluid-filled matrix.
(Photosynthesis) How does the structure of the chloroplast maximise the rate of the light-DEPENDENT reaction?
ATP synthase channels within granal membrane.
Large surface area of thylakoid membrane for ETC.
Photosystems position chlorophyll to enable maximum absorption of light.
(Photosynthesis) How does the structure of the chloroplast maximise the rate of the light-INDEPENDENT reaction?
Own DNA & ribosomes for synthesis of enzymes e.g. rubisco.
Concentration of enzymes & substrates in stroma is high.
(Photosynthesis) Define ‘limiting factor’.
Factor that determines maximum rate of a reaction, even if other factors change to become more favourable.
(Photosynthesis) Name 4 environmental factors that can limit the rate of photosynthesis.
1) Light intensity (light-dependent stage)
2) CO2 levels (light-independent stage)
3) Temperature (enzyme-controlled steps)
4) Mineral/magnesium levels (maintain normal functioning of chlorophyll)
(Photosynthesis) Outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis.
- Artificial light, especially at night
- Artificial heating
- Addition of CO2 to greenhouse atmosphere
(Photosynthesis) Why do farmers try to overcome the effect of limiting factors?
- To increase yield.
- Additional cost must be balanced with yield to ensure maximum profit.
