photosynthesis

Question 1

What are the stages
of photosynthesis?

Answer 1

1. Light dependent reaction
   ○ Thylakoid membrane of chloroplast
2. Light independent reaction
   ○ Stroma of chloroplast

Question 2

desribe photoionisation in LDR

Answer 2

● Chlorophyll absorbs light energy which excites its electrons (higher energy level)
● So electrons are released from chlorophyll (chlorophyll becomes positively charged)

Question 3

describe what happens after photoionisation in LDR

Answer 3

Some energy from electrons released in photoionisation is conserved in the production of ATP / reduced NADP
(chemiosmotic theory):
1. Electrons move along electron transfer chain (electron carriers), releasing energy
2. This energy is used to actively pump protons from stroma into thylakoid
3. Protons move by facilitated diffusion down electrochemical gradient into stroma via ATP synthase
4. Energy used to join ADP and Pi to form ATP (photophosphorylation)
5. NADP accepts a proton and an electron to become reduced NADP

Question 4

describe photolysis of water in LDR

Answer 4

● Water splits to produce protons, electrons and oxygen (H2O → 1⁄2 O2 + 2e + 2H+
○ Electrons replace those lost from chlorophyll

Question 5

Describe the light-independent reaction of photosynthesis (Calvin cycle)

Answer 5

1. CO2 reacts with ribulose bisphosphate (RuBP)
   ○ Catalysed by the enzyme rubisco
2. Forming 2 glycerate 3-phosphate (GP) molecules
3. GP reduced to triose phosphate (TP)
   ○ Using products from light-dependent reaction - reduced NADP and energy from ATP
4. Some TP converted to useful organic substances (eg. glucose)
5. Some TP used to regenerate RuBP in the Calvin cycle (using energy from ATP)