3.5.1: Photosynthesis

Question 1

What are the two stages of photosynthesis?

Answer 1

-Light dependent reaction
- Light independent reaction

Question 2

Describe the LDR

Answer 2

1) Photoionisation. Chlorophyll absorbs light energy. Excites electrons.

2) Electrons moves down electron transport chain releasing energy. Energy released to forms proton electrochemical gradient.

3) Photophosphorylation. H+ ions disuse through ATP synthase providing energy to join ADP and Pi to form ATP

4) Photolysis. H2O -> 2e- + 2H+ + 1/2O2. NADP reduced by hydrogens. Electrons replaces those lost

Question 3

Where does the LDR occur?

Answer 3

Thylakoid membrane

Question 4

Where does the LIR occur?

Answer 4

stroma

Question 5

Why is LIR temperature sensitive?

Answer 5

Contains enzymes

Question 5

Describe LIR (Calvin cycle)

Answer 5

1) Fixation - RuBP combines with CO2 using the enzyme rubisco to form two GP.

2) Reduction - GP is reduced to TP using NADPH and ATP. Some TP converted into useful organic products e.g. carbohydrates, amino acids and triglycerides

3) Regeneration - Most TP is regenerated back to RuBP using energy from ATP

Question 6

What are the three limiting factors?

Answer 6

1) CO2 concentration
2) Light intensity
3) Temperature

Question 7

Describe temperature on the rate of photosynthesis

Answer 7

• Low temperature = lower rate of reaction because not enough successful collisions, not enough enzyme substrate complexes
• High temperature = enzyme denatures

Question 8

Why does CO2 limit rate of photosynthesis?

Answer 8

Reactant in Calvin cycle

Question 9

Why does light intensity limit rate of photosynthesis?

Answer 9

Light is needed in LDR for photolysis and photoionisation