Hi all....
Not sure if everyone received their photosynthesis tutorials... they were at the class bench today...
And since they didnt go through the tutorial... I'll try to post the answers here. Please edit if they are wrong (and highlight!!)
1. A
2. D - Thylakoid membrane
3. B
4. D
5. B - Temperature is optimum, CO2 in low conc.
6. C
7. D - Stroma
8. C - NADPH and ATP used in reaction, RuBP is recycled, GP(PGA) is produced.
9. B
10. D* (not too sure). O2 produced by photolysis, so supplying 18O2 shouldnt have any effect on the photolysis of H2O.
11. C
12. C
13. A - Carbon fixation
14. B - Compensation point
15. D
16. B
17. B - DCMU is an electron acceptor, hence it prevents the ETC from functioning.
18. A
19. C
20. C - DCPIP is also an electron acceptor
21. B
22. D - Relatively high rate of photosynthesis at low light intensity, low maximum rate of photosynthesis.
23. C
24. A - Chlorophyll A donates the excited electron from water.
25. C
26. D
27. B - reduced NADP is NADPH. Don't get confused.
28. C
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Structured qns.
1(a). Location of photophosphorylation: ATP synthase in the thylakoid membrane of chloroplasts.
1(b).
Cyclic photophosphorylation:
- Only ATP produced, no NADPH produced
- Only PS I is involved
- Photolysis of water does not take place / Water is not required
- Oxygen is not produced
Non-cyclic photophosphorylation:
- Both ATP and NADPH is produced
- Both PS I and PS II involved
- Photolysis of water takes place
- Oxygen is produced as a by product
2(a) Location of Calvin cycle: Stroma of chloroplasts
2(b) Carbon fixation: RuBP + CO2 -> GP(PGA)
ATP converted to ADP: GP -> TP (PGAL) and also at the regeneration of RuBP
Reduced NADP oxidised: GP -> TP(PGAL), after ATP -> ADP
Glucose is synthesised: TP(PGAL) -> Synthesis of glucose
2(c) Role of water in light dep. stage:
- Split into protons, electrons, and oxygen by PS I
- Protons used to increase proton gradient between thylakoid lumen and stroma for the synthesis of ATP /phosphorylation of ADP to ATP
- Electrons used as energy carriers when excited ( in Photosystem II when an electron is emitted at high energies from P680, electron from photolysis fills up the electron gap, allowing cycle to continue.)
3(a)(i) NaH14CO3 - to supply 14CO2 by decomposition, 14CO2 used as radioactive marker to trace path of CO2 through the photosynthetic processes
3(a)(ii) Hot alcohol - organic solvent, dissolves membranes and chlorophyll / contents of chloroplast, extracting metabolites for chromatography. Kills cell and immobilises molecules to prevent further reaction
3(a)(iii) Photographic plate: To detect presence of 14C isotopes in the chromatograms
3(b) Light independant stage (CO2 is only involved in light indep. stage)
3(c) Glycerate-3-phosphate / 3-Phosphoglycerate / refer to notes XD
4(a)(i) Limiting factor: Light intensity
4(a)(ii) Light is saturated and is no longer a limiting factor. Other factors such as CO2 concentration and temperature becomes the limiting factor.
4(a)(iii) Light is usually present in excess in nature, hence rate of photosynthesis is limited by other factors such as concentration of CO2 and temperature, hence any change in CO2 concentration or temperature will directly affect the rate of photosynthesis. Any small variation in light intensity can thus be said to have no effect on the rate of photosynthesis.
4(b) Photosynthesis is largely enzyme controlled, hence rate of photosynthesis is proportional to rate of enzyme action. At low light intensities the light intensity is limiting, hence rate of photosynthesis is affected primarily by light intensity and not temperature. At high light intensities, light is no longer limiting, hence for the same CO2 concentration the temperature is limiting. A temperature of 25C is closer to the optimum temperature of the enzymes involved in photosynthesis than 15C. The substrate particles have more kinetic energy, leading to an increase in enzymatic activity.
4(c) Carbon dioxide is a limiting factor of photosynthesis in nature. From Fig 1, Graph A shows that the rate of photostynthesis can be increased up to 12 au in 0.4% CO2, whereas for graph C the maximum rate of photosynthesis is only at 2 au. This shows that the rate of photosynthesis can be increased up till CO2 concentrations of 0.4%, which is much higher than the atmospheric concentration of 0.035%.
4(d) - Amount of water - water is required for photolysis, generating protons and electrons for the synthesis of ATP and NADPH required by the light independent stages.
- Concentration of oxygen - oxygen is a competitive inhibitor of RuBisCO, an enzyme crucial for carbon fixation in the light independant stage / Calvin cycle. Oxygen competes with CO2 for the active site of RuBisCO, reducing the rate of photosynthesis.
- Presence of poisons/enzyme inhibitors - Poisons may affect the ETC by serving as electron acceptors, inhibiting the production of NADPH.
- Deficiency of essential ions required for chlorophyll - Unable to harvest light, reducing rate of photolysis, hence reducing rate of photosynthesis.
- Presence of pollutants - may damage leaves, ie blocking stomata or reducing transparency of epidermis, hence reducing rate of photosynthesis.
4(e) Adenosine Triphosphate (ATP) and reduced Nicotinamide Adenine Dinucleotide Phosphate (NADPH)
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Essay Qn: All in one (lazy to write individually)
- Light harvested in thylakoid membrane of chloroplasts
- Photosynthetic pigments in the photosytems such as chlorophyll b and carotenoids harvest and focus the light energy on to a pair of special chlorophyll a molecules (P680) in the reaction center of photosystem II via resonance energy transfer.
- Photolysis of water to form 2 protons, 2 electrons and oxygen by light per molecule of H20
- Oxygen released as a by product
- Hydrogen accumulates in thylakoid lumen, increases proton gradient btwn thylakoid lumen and stroma
- Electrons produced are used to replenish the electron lost by excitation from special chloroplast a
- PS II excites electrons to be received by an electron acceptor
- Transported through electron transport chain via plastoquinone, cytochrome b6f complex, plastocyanin. Energy is lost in the process.
- Reduction and oxidation of plastoquinone pumps protons into thylakoid lumen against concentration gradient, expands energy in the process, further increasing the proton gradient between the thylakoid lumen and the stroma.
- Electrons excited again in PS I by P700 in the reaction center by light energy transferred by accessory pigments
- Transferred to ferredoxin, then to NADP+ reductase
- NADP+ as final electron acceptor, forming NADPH
- Proton gradient created used to drive photophosphorylation of ADP to ATP via a catalyst, ATP synthase
- ATP and NADPH produced used to link and drive the Calvin cycle
- In the stroma, 3 molecules of Ribulose bisphosphate (RuBP) and 3 molecules of CO2, catalysed by RuBP carboxylase oxygenase (RuBisCO) to produce an unstable 6 carbon intermediate that spontaneously breaks down to form 6 molecules of Glycerate-3-phosphate (GP)
- GP is phosphorylated by ATP to form Glycerate-1,3-bisphosphate (BPG), producing ADP
- BPG is reduced by NADPH to form Glyceraldehyde-3-phosphate (G3P), producing NADP+ and an inorganic phosphate group
- ADP, NADP+ and the inorganic phosphate group are recycled in the light dependant stage
- 1 molecule of G3Pexits the cycle and is used to store chemical energy in the form of carbohydrates such as glucose or fructose, or for the synthesis of lipids, amino acids, and nucleic acids.
- The remaining 5 molecules of G3P are used to regenerate the 3 molecules of RuBP for the cycle.
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Please add on if I lack anything!!! And.. thanks to Chao Tong for correcting my mistakes =)
Jiayou for bio test!!
Cheers,
JJ
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