photosynthesis stages

Question 1

What is photophosphorylation? (1)

Answer 1

The addition of phosphate in the presence of light to produce ATP

Question 2

Describe cyclic photophosphorylation (3)

Answer 2

1. Only produces ATP,
2. Electrons from chlorophyll are passed back to PSI and are recycled,
3. No reduced NADP or O₂ is produced

Question 3

Describe non-cyclic photophosphorylation (1)

Answer 3

Produces ATP, reduced NADP, and O₂

Question 4

What happens during photoionisation of chlorophyll in the light-dependent reaction? (2)

Answer 4

1. Light energy absorbed by PSII excites electrons in chlorophyll,
2. High-energy electrons move along the electron transport chain to PSI

Question 5

What is photolysis, and what are its products? (2)

Answer 5

1. Photolysis is the splitting of water using light energy,
2. It produces protons (H⁺), electrons, and oxygen (H₂O → 2H⁺ + ½O₂)

Question 6

How is ATP produced in the light-dependent reaction? (5)

Answer 6

1. Electrons move down the electron transport chain, losing energy at each stage,
2. This energy is used to pump protons into the thylakoid space, creating a proton gradient,
3. Protons move back into the stroma via ATP synthase,
4. Producing ATP from ADP + Pi,
5. This process is called chemiosmosis

Question 7

What happens when light energy is absorbed by PSI? (2)

Answer 7

1. Electrons are excited to a higher energy level and are transferred to NADP, along with a proton (H⁺),
2. Forming reduced NADP

Question 8

Where do the products of the light-dependent reaction go? (2)

Answer 8

1. ATP and reduced NADP diffuse into the stroma,
2. Where they are used in the light-independent reaction (Calvin cycle)

Question 9

What happens during CO₂ fixation in the Calvin cycle? (3)

Answer 9

1. CO₂ combines with ribulose bisphosphate (RuBP) (5C) in the presence of the enzyme RuBisCo,
2. This forms an unstable 6C compound,
3. Which breaks down into two molecules of glycerate-3-phosphate (GP) (3C)

Question 10

How is GP converted into triose phosphate (TP)? (2)

Answer 10

1. GP is reduced to TP using reduced NADP from the light-dependent reaction and energy from ATP,
2. The resulting NADP is recycled back to the light-dependent reaction

Question 11

How is ribulose bisphosphate (RuBP) regenerated in the Calvin cycle? (2)

Answer 11

1. 5 out of 6 molecules of TP are used to regenerate RuBP using ATP,
2. The remaining 1 out of 6 TP is used to produce useful organic substances like glucose

Question 12

What substances are used in the light-dependent stage of photosynthesis? (4)

Answer 12

1. Water,
2. Inorganic phosphate,
3. ADP,
4. NADP

Question 13

What substances are used in the light-independent stage of photosynthesis? (4)

Answer 13

1. Reduced NADP,
2. ATP,
3. Carbon dioxide,
4. Ribulose bisphosphate

Question 14

What are the end products of the light-dependent stage of photosynthesis? (3)

Answer 14

1. ATP,
2. Reduced NADP,
3. Oxygen

Question 15

What are the end products of the light-independent stage of photosynthesis? (4)

Answer 15

1. NADP,
2. ADP,
3. Inorganic phosphate,
4. Carbohydrate