5.2.1: Photosynthesis

Question 1

Photosynthesis is a form of

Answer 1

autotrophic nutrition

Question 2

Compensation point

Answer 2

when rate of photosynthesis = rate of respiration

Question 3

Chloroplast adaptations

Answer 3

• Thylakoid membrane highly folded into many grana –> high SA for photosynthetic pigments, electron carriers and ATP synthase
• Photosynthetic pigments arranged into photosystems –> enables maximum adsorption of light energy
• Chloroplast DNA and 70s ribosomes –> can immediately make some of the proteins needed for photosynthesis

Question 4

What are the two stages of photosynthesis?

Answer 4

• Light-dependent stage

* Light-Independent stage

Question 5

Light dependent stage summary

Answer 5

• Energy from light absorbed, used to form ATP
• hydrogen from water used to turn NADP into reduced NADP
• oxygen is a by-product of this stage

Question 6

Light independent stage summary

Answer 6

• Hydrogens from reduced NADP combined with CO₂ to build organic molecules e.g. glucose
• ATP supplies the energy required for this

Question 7

What is a photosynthetic pigment?

Answer 7

• a pigment that absorbs light of a specific wavelength. Different pigments absorb different wavelengths of light.
• Can release excited electrons once it has absorbed light
• Used in the light-dependent stage of photosynthesis
• Located in photosystems on the thylakoid membrane

Question 8

What is a light harvesting system?

Answer 8

Photosynthetic pigments and proteins

Question 9

What is a photosystem?

Answer 9

Light harvesting system and the reaction centre

Question 10

What is the role of the light harvesting system?

Answer 10

To absorb light of different wavelengths and transfer this energy to the reaction centre.

Question 11

Non-cyclic photosphorylation uses which photosystem(s)?

Answer 11

1 and 2

Question 12

Cyclic photophosphorylation uses which photosystem(s)?

Answer 12

1

Question 13

Non-cyclic photophosphorylation produces

Answer 13

• ATP ( by chemiosmosis from ETCs 1 &2)
• Reduced NADP (from PS1 ETC)
• Oxygen as a by-product of photolysis

Question 14

Cyclic photophosphorylation produces

Answer 14

• ATP by chemiosmosis

✖️ Does not produce reduced NADP

Question 15

Photolysis (equation)

Answer 15

H₂O ⟶ 2H⁺ + 2e⁻ + ½O₂

Question 16

What happens to the e- produced in photolysis?

Answer 16

They replace the e- last from the PS2 reaction centre.

Question 17

What happens to the H⁺ produced in photolysis?

Answer 17

• Released into the lumen of the thylakoid
• Diffuse back through membrane down concentrations and electrochemical gradient (driving ATP formation in the process)
• Once H⁺ returned to stroma, combine with NADP and an e- from PS1 to form reduced NADP
• This combining with NADP removes H⁺ ions from the stroma, maintaining the proton gradient across the thylakoid membrane

Question 18

Products of the light dependent stage that are needed for the light independent stage

Answer 18

• ATP

* Reduced NADP

Question 19

Where does the light independent stage take place?

Answer 19

In the stroma of the chloroplast

Question 20

Where does the light dependent stage take place?

Answer 20

On the thylakoid membrane

Question 21

The light dependent stage uses what as a raw material?

Answer 21

Water

Question 22

The light independent stage uses what as a raw material?

Answer 22

Carbon dioxide

Question 23

Three main stages of the Calvin cycle?

Answer 23

1) Fixation
2) Reduction
3) Regeneration

Question 24

Differences between cyclic and non-cyclic photophosphorylation

Answer 24

Non-cyclic
• O₂ produced through photolysis
• Reduced NADP produced
• Uses PS1 & 2

Cyclic
• No O₂ produced
• No reduced NADP produced
• Uses PS1 only

Question 25

How many turns of the Calvin cycle are required to make one glucose molecule?

Answer 25

6
• Because per turn, 2 x TP produced
• 1 of every 6 TP goes towards glucose

Question 26

Uses of triose phosphate (TP)

Answer 26

• Starting material for synthesis of carbohydrates, lipids, amino acids
• For regeneration of RuBP

Question 27

What is Ribulose bisphosate carboxylase (RuBisCO)?

Answer 27

Enzyme that catalyses the reaction between RuBP and CO₂ to form an unstable intermediate.

Question 28

What is RuBP?

Answer 28

Ribulose bisphosphate: five carbon molecule used in the Calvin cycle.