5.1 - Photosynthesis

Question 1

Where does the light dependent stage occur?

Answer 1

in the thylakoid membranes/grana

Question 2

Where does the light independent stage occur?

Answer 2

stroma

Question 3

Describe photolysis

Answer 3

• chlorophyll absorbs light energy to split water into oxygen, H+ and e-
• H+ and electrons used to form NADPH for LIR
• electrons passed along electron transport chain
• oxygen for respiration or diffuses out through stomata

Question 4

Describe photoionisation

Answer 4

• light energy ‘excites’ electrons in chlorophyll, where they raise up an energy level
• some energy released used to make ATP and reduced NADP in chemiosmosis

Question 5

Describe chemiosmosis

Answer 5

• electrons move along series of proteins (electron transport chain)
• release energy at each movement
• energy used to actively transport H+ ions across membrane from stroma into intermembrane space
• creates electrochemical gradient
• H+ ions diffuse through ATP synthase back into stroma
• causes ATP synthase to change in shape and energy released catalyses ATP synthesis
• H+ ion and electrons combine with co-enzyme NADP -> NADPH

Question 6

Describe the first stage of the Calvin Cycle (LIR)

Answer 6

Carbon fixation: CO2 ‘fixes’ RuBP into 2 molecules of GP
catalysed by the enzyme rubisco

Question 7

Describe the second stage of the Calvin Cycle

Answer 7

GP is reduced to triose phosphate using ATP hydrolysis and by accepting H from NADPH from LDR

Question 8

What is triose phosphate used for?

Answer 8

• to regeneration RuBP in Calvin Cycle
• converted to useful organic substances

Question 9

Describe the third stage of the Calvin Cycle

Answer 9

RuBP is regenerated using energy released from ATP hydrolysis

Question 10

Name the 3 factors which are limiting factors for photosynthesis

Answer 10

• temperature
• CO2 concentration
• light intensity
  (see graphs - temperature is different to other two)