Photosynthesis (easy)

Question 1

Compare absorption spectrum of chl a & chl b [2]

Answer 1

D: compare peaks; give (x: wavelength, y: % light absorption)

S1: Higher absorption of blue light and red light
S2: Peaks in blue light higher than red light
S3: Least absorption of green light

Question 2

Explain the shape of the action spectrum [2]

Answer 2

1. Peaks correspond to peaks of absorption spectra
   » higher rate of photosynthesis in red and blue light
2. Region (500-600 nm) not an exact match between absorption and action spectra
   » due to accessory pigments that pass the energy via resonance to reaction centre
   » FUNCTION: widen action spectrum - absorb LE of different wavelengths

Question 3

Explain how an electron carrier inhibitor acts as an effective herbicide [3]

Answer 3

1. Electrons cannot be passed down ETC
2. No NADPH produced
3. No pumping of protons across thylakoid membrane from stroma to thylakoid lumen
   » no proton gradient&raquo_space; no chemiosmosis&raquo_space; no ATP produced
4. No CC&raquo_space; no GP&raquo_space; G3P produced for respiration

Question 4

Explain role of thylakoid membrane [3]

Answer 4

CHEMIOSMOSIS:

1. Hydrophobic core&raquo_space; impermeable to H+&raquo_space; establish H+ gradient
2. Sequential order of electron carriers&raquo_space; energy released to pump H+&raquo_space; establish H+ gradient
3. Large SA&raquo_space; many ATP synthases&raquo_space; ATP synthesis

CC:

4. Large SA&raquo_space; many NADP reductase&raquo_space; reduce NADP

Question 5

Explain how LDR is linked to LIR

Answer 5

1. NADPH - reduce GP to G3P
2. ATP - energy for reduction stage
3. ATP - regeneration of RuBP&raquo_space; continue CC

Question 6

Explain role of water [2]

Answer 6

Photolysis…

1. H+ - establish H+ gradient
2. Electrons - replace electrons lost by chl a in PS II

Question 7

Compare cyclic vs. non-cyclic photophosphorylation [3]

Answer 7

1. End-product
   » only ATP vs. ATP, NADPH, O2
2. PS involved
   » PS I only vs. PS I and II
3. Source of electrons / electron donor
   » P700 vs. water, direct electron donor is P680
4. Pathway of electrons
   » cyclical (PS I > 1st ETC > PS I) vs. 1 direction (PS II > 1st ETC > PS I > 2nd ETC)
5. Final electron acceptor
   » P700 vs. NADP+

Question 8

Explain how O2 consumption and succinic acid oxidation are linked [2]

Answer 8

1. FAD reduced to FADH2 (ELECTRONS DONATED) in breakdown of succinate
2. O2 as final electron acceptor
   » maintains flow of electrons down ETC
3. FADH2 can donate electrons to ETC
   » regenerate FAD+

Question 9

Compare SLP and OP

Answer 9

1. Role of coenzyme
   SLP - NAD+ needed for oxidation of G3P
   OP - NADH and FADH2 pass electrons to ETC
2. Enzyme
   » kinase vs. ATP synthase
3. ATP synthesis
   SLP - enzymatic transfer of phosphate from substrate to ADP via a kinase
   OP - due to diffusion of H+ down H+ gradient from IMS to MM via ATP synthase
4. Source of phosphate
   » organic molecule vs. inorganic phosphate
5. (transfer of electrons down) ETC and (generation of) H+ gradient
6. ATP yield / glucose (2 vs. 32/34)

Question 10

Explain why rate of O2 uptake can be used as an indicator of rate of respiration [2]

Answer 10

Final electron acceptor in OP

Question 11

Explain why glucose has no effect on rate of O2 uptake by ISOLATED MITOCHONDRIA [2]

Answer 11

1. No enzymes for glycolysis
2. Glucose not oxidised to pyruvate
   » no acetyl CoA produced for KC
   » no NADH/FADH2 produced to donate electrons to ETC for OP
3. Thus O2 not reduced to produce water

Question 12

Explain the different yields of ATP from glycogen and palmitic acid [2]

Answer 12

1. Palmitic acid yields higher energy
2. Palmitic acid has more C-H per mole
3. More H+ released for chemiosmosis in OP
   » produce more ATP

Question 13

Explain ATP’s “universal role as the energy currency” [4]

Answer 13

1. Immediate source of energy in most cells
   » easily hydrolysed to ADP + Pi + energy
   » used in metabolic reactions - link catabolic + anabolic reactions
   » reversible reaction&raquo_space; high turnover
2. Small, water soluble&raquo_space; diffusible around cell