Topic 5

Question 1

Where do
-the LDR
-the LIR
of photosynthesis occur?

Answer 1

LDR: In thylakoids of chloroplasts
LIR: In stroma of chloroplasts

Question 2

Photoionisation of chlorophyll

Answer 2

• Light energy absorbed by chlorophyll
• Electrons become excited and raise up an energy level
• Electrons released from chlorophyll

Question 3

Electron transfer chain
- what is it?
- what happens?

Answer 3

The ETC is a series of carrier proteins embedded in the thylakoid membrane.

Electrons (released from cholorophyll in photoionisation) move along the ETC and undergo a series of redox reactions and release energy at each carrier protein.

Question 4

Chemiosmosis: how is a proton concentration gradient established?

Answer 4

Energy released from electrons in the ETC is used in the active transport H+ ions (protons) from the stroma into the thylakoid space.
So there is a higher concentration of protons in the thylakoid space than in the stroma —> establishes conc. gr.

Question 5

Chemiosmosis: how is ATP produced in the LDR?

Answer 5

Protons move down their concentration gradient (from thylakoid space back into the stroma) via facilitated diffusion, through ATP synthase channel protein

ATP synthase catalyses the condensation of ADP and inorganic phosphate (Pi) to make ATP

Question 6

Photolysis of water

Answer 6

Light energy splits molecules of water
Products: oxygen, electrons, protons

Question 7

How is reduced NADP produced

Answer 7

NADP is a coenzyme that carries Hydrogen. Hydrogen reduces NADP —> NADPH

NADP picks up H+ ions (protons) and electrons (from the photolysis of water and in the electron transfer chain)

Question 8

LIR: The Calvin Cycle
- outline the main stages

Answer 8

Carbon fixation
Reduction
regeneration

Question 9

The Calvin Cycle

Answer 9

• CO2 enters cycle and reacts with RuBp
• reaction catalysed by enzyme rubisco
• forms unstable 6C intermediate —> breaks down into 2 molecules of GP
• 2x GP are reduced to 2x TP
• requires energy: from hydrolysis of 2x ATP —> ADP +Pi
  -requires 2x reduced NADP which donates H atom to reduce GP to TP
  -some TP (1C) leaves cycle —> useful organic substances
  -some TP used to regenerate RuBP

Question 10

Role of triose phosphate in Calvin Cycle

Answer 10

Some leaves cycle and is converted into useful organic substances

Some used to regenerate RuBP
- this requires energy: from the hydrolysis of ATP —>ADP + Pi

Question 11

Roles of ATP and NADPH

Answer 11

ATP: hydrolysed to provide energy to reduce GP and regenerate RuBP
NADPH: donates H (electrons in it) for reduction of GP to TP