13 Photosynthesis

Question 1

Describe the use of chromatography to separate and identify chloroplast pigments

Answer 1

1 spot / extract, placed on, pencil line / base line / line of origin ;
2 repeat / concentrate, spot / extract ;
3 end / base, of paper, suspended / placed, in (named) solvent ;
4 mark the solvent front after, some time / paper removed / solvent moves ;
5 Rf value = distance moved by, spot / pigment / component / solute ÷ distance moved by solvent (front) ;
6 compare (R) with known R, values to identify, constituents / pigments ;
7 detail of method ;

Question 2

Explain why chloroplasts have different coloured pigments to function efficiently

Answer 2

1 pigments absorb/capture/harvest light energy
2 increases range of wavelengths that can be absorbed
3 increase, efficiency / rate, of, photosynthesis / light dependent reaction
4 e.g. of 2 pigments: chlorophyll a, xanthophyll, carotenoids, chlorophyll b

Question 3

Explain the relationship between absorption spectra and action spectra

Answer 3

1 action (spectrum) shows rate of photosynthesis for light, wavelengths / colours ;
2 absorption (spectrum) shows how much each, wavelength / colour, is absorbed ;
3 higher absorption gives higher photosynthesis ;

Question 4

Explain why temperature can be a limiting factor in photosynthesis

Answer 4

1 ref. (named) enzymes ;
2 high(er) temperature increases rate ;
3 (temperature affects) photophosphorylation / light-dependent / Calvin cycle / light-independent / ESC formation;
4 enzymes denature at, too high a temperature / very high temperature / above optimum temperature ;

Question 5

Outline how the light independent stage of photosynthesis leads to the production of carbohydrates in plant leaves

Answer 5

1 RuBP joins with CO2 to make, 6C intermediate / GP ;
2 GP to TP ;
3 (GP → TP) uses ATP and reduced NADP ;
4 TP → glucose /hexose → starch ;
5 condensation / polymerisation / glycosidic bonds ;

Question 6

Explain the adaptations of grana

Answer 6

1 thylakoid stacks or discs/ many thylakoids, for, increased or large, surface area ;
2 increased or large, surface area maximises the absorption of light (energy) / AW; Ignore trap (light energy)
mp 3-5 thylakoid membranes / grana contain
photosynthetic / named / primary / accessory, pigments to absorb light (energy) ;
4 electron carriers / ETC, to, transfer / release, energy (from excited electrons) ;
5 photosystems / antenna complex and reaction centre, are light harvesting structures ;
6 thylakoid space or lumen to, form proton gradient/ have high concentration of protons ;
7 thylakoid membrane is (relatively) impermeable, to maintain the proton gradient (for chemiosmosis) ;
8 ATP synthase to make ATP ;
9 contains oxygen-evolving complex/OEC, for the photolysis of water ;

Question 7

Outline the main features of cyclic photophosphorylation

Answer 7

1 only involves photosystem I ;
2 light energy absorbed (by accessory pigments) ;
3 passed on to, chlorophyll a / primary pigment / reaction centre ;
4 electron, excited to higher energy level / emitted from chlorophyll ;
5 collected by electron acceptor ;
6 passed along electron transport chain ;
7 ATP produced by chemiosmosis ;
8 electron returns to chlorophyll ;

Question 8

Describe an investigation using redox indicators to determine the effects of light intensity and light wavelength on the rate of photosynthesis

Answer 8

1 Hill reaction ;
2 oxidised DCPIP is blue ;
3 (DCPIP) goes colourless when reduced ;
4 method for making chloroplast, extract / suspension ;
5 ref. to buffer solution / control osmosis / control pH ;
6 expose chloroplasts + DCPIP to wavelength of light;
7 (method 1) measure time for, blue to disappear / blue-green - green / colour to match control with no DCPIP (method 2) leave for fixed time and measure with colorimeter ;
8 calculate rate as, (method 1) 1/t or
(method 2) change in colour value divided by time ;
9 test five (or more), wavelengths / colours;
10 do three repeats / calculate means :
11 plot wavelength on x-axis against, dependent variable / calculated rate, on y-axis ;

Question 9

Explain the process of non-cyclic photophosphorylation

Answer 9

1. photosystem I (PI) and photosystem II (PII) involved ;
2. light harvesting clusters ;
3. light absorbed by accessory pigments ;
4. primary pigment is chlorophyll a ;
5. energy passed to, primary pigment / chlorophyll a ;
6. electrons, excited / raised to higher energy level ;
7. (electrons) taken up by electron acceptor ;
8. (electrons) pass down electron carrier chain (to produce ATP) ;
9. PII has (water splitting) enzyme ;
10. water split into protons, electrons and oxygen ;
11. photolysis ;
12. electrons from PII pass to PI / electrons from water pass to PII ;
13. to replace those lost ; give either in relation to PI or PII
14. protons and electrons combine with NADP (to produce reduced NADP) ;