Photosynthesis

Question 1

Parts of the chloroplast involved in photosynthesis

Answer 1

1. Thylakoid membrane
   where photosystems located
   where photosynthetic pigments located
   ETCs located
   enzymes NADP+ reductase and ATP synthase embedded
   through which H+ ions diffuse through during chemiosmosis
2. Thylakoid space
   where chemiosmosis take place during which H+ ions build up and accumulate forming a proton gradient
3. Intergranal lamella links grana together
4. granum
   a stack of thylakoids
   5.Stroma where chemiosmosis take place
   H+ diffuse from thylakoid space to here
   where light independent stage occurs (calvin’s cycle)

Question 2

Photosynthetic pigments

Answer 2

1.Chlorophyll a (main; primary pigment) directly involved in photosynthesis
2.Chlorophyll b ( accessory pigments)
indirectly involved in photosynthesis
channels light energy absorbed to chlorophyll a
these pigments mainly absorb red and blue light
3.Carotenoids (accessory pigment)
indirectly involved in photosynthesis)
photoprotective role of absorbing and dissipating excess light energy

Question 3

Absorption spectrum

Answer 3

Rate of photosynthesis against wavelength of light with all pigments combined

Question 4

Action spectrum

Answer 4

Rate of photosynthesis against wavelength of light with different photosynthetic pigments

Question 5

Why the action spectrum and absorption spectrum looks similar but not identical

Answer 5

The presence of various other photosynthetic pigments other than chlorophyll a that can absorb wavelengths of light that chlorophyll a cannot therefore broadening the spectrum of wavelength of light at which photosynthesis can occur causes slight variations between the two graphs

Question 6

Photosystems I and II

Answer 6

PSII + PSI (non cyclic photophosphorylation)
PSII cont. P680 primary pigment mol.

PSI (cyclic photophosphorylation)
PSI cont. P700 primary pigment mol.
both located on thylakoid membrane

Question 7

Non cyclic

Answer 7

1.Photoexcitation of chloroplasts in PSII LHC
2.Photolysis of water
3. Electrons transferred down ETC 1 to PSI
ATP produced
4. Photoexcitation of chloroplasts in PSI LHC
5. Electrons transferred down ETC 2
NADPH produced

first electron donor: water
final electron acceptor NADP+

Question 8

Cyclic

Answer 8

1. Photoexcitation of chloroplasts in PSI LHC
2. Electrons from P700 to PEA to ETC 1 through cytochrome complex.
3. chemiosmosis occurs to produce ATP

first electron donor: P700
final electron acceptor: P700

Question 9

Chemiosmosis

Answer 9

1. in non cyclic/cyclic involves the cytochrome complex, H+ ions from photolysis and in cell and ATP synthase

Question 10

Light independent (Calvin’s cycle)

Answer 10

1. Carbon fixation
2. Reduction
3. Regeneration of RuBP

Question 11

Carbon fixation

Answer 11

CO2 enters the calvin cycle and combines with RuBP (5C) to form an unstable 6C cmpd that immediately splits in half to form 2 3C cmpd- 3-phosphoglycerate. This is catalysed by Rubisco

Question 12

Reduction

Answer 12

3-phosphoglycerate is phosphorylated by ATP to form 1,3 bisphosphoglycerate which is then reduced by NADPH to form triose phosphate (G3P) 5 mol used in regeneration of RuBP, 1 mol used in synthesis of sugars such as glucose

Question 13

Regeneration of RuBP

Answer 13

in last stages of calvin cycle, 5 molecules of G3P is rearranged to form RuBP and cycle repeats

Question 14

Limiting factors of photosynthesis

Answer 14

1. Light intensity
2. temperature
3. oxygen concentration
   oxygen is a competitive inhibitor of Rubisco. It competes for the active site of rubisco with CO2
4. carbon dioxide concentration
   directly affects calvin cycle
   decreased, 3PG production reduced, 1-3 BPG reduced, G3P reduced, RuBP accumulates

Question 15

Compensation point

Answer 15

Rate of photosynthesis = rate of respiration