Calvin cycle

Question 1

How does carbon dioxide enter the stroma?

Answer 1

• enters the intercellular spaces w/in the spongy mesophyll of leaves by diffusion
• from atmosphere through stomata
• diffsued into cells

Question 2

What does carbon dioxide combine with?

Answer 2

• combined with a 5C molc called ribulose biphosphate (RuBP)

Question 3

what does it mean that the carbon dioxide is fixed?

Answer 3

it is incorporated into an organic molecule

Question 4

What does the fixation of carbon dioxide result in? How does this occur?

Answer 4

• enzyme ribulose biphosphate carboxylate (RuBisCO) catalyses the reaction between carbon dioxide and ribulose biphosphate
• an unstable 6C intermediate is produced
  
  • immediately breaks down to 2 3C carbon glycerate 3-phosphate (GP) molecules

Question 5

What is ribulose biphosphate carboxylase inhibited by?

Answer 5

• competitively inhibited by oxygen
• very inefficient
• a lot is needed

Question 6

WHat is each GP molecule converted to? How does this occur?

Answer 6

• converted to another 3C molc, triose phosphate (TP)
  
  • uses 2 ATP and 2 reduced NADP
  • • both supplied from the light-dependant reactions of photosynthesis

Question 7

What is triose phosphate

Answer 7

• 3C sugar, carbohydrate

Question 8

What happens to the triose phosphate?

Answer 8

• majority recycled to regenerate ribulose biphosphate so the Calvin cycle
  
  • using 1 ATP molecul
• it is the starting point for many complex biological molc
  
  • including other carbs, lipids, proteins, and nucleic acids

Question 9

Summarise the calvin cycle in 3 steps?

Answer 9

• Fixation
  
  • carbon dioxide is fixed in the first step
• reduction
  
  • GP reduced to TP by the addition of H from reduced NADP using E supplied from ATP
• regeneration
  
  • RuBP regenerated from the recycled TP

Question 10

What happens for one glucose molc to be produced?

Answer 10

• 6 CO2 molc have to enter Calvin cycle
  
  • resulting in six full turns of the cycle
• results in production of 12 TP molc
  
  • 2 of which used to make glucsose
  • 10 TP recycled t oregernate 6 RuBP molc
    
    • used in 6 turns of the cycle

Question 11

How does loss of water prevent photosynthesis?

Answer 11

• leads to closure of stomata
• oxygen builds up as the plant will continue to photosyntheise
• oxygen competitively inhibits RuBisCO
  
  • reducing production of GP
• produces toxic 2C product, convered by organic molc and energy from ATP needed
• RuBisCO has higher affinity for oxygen

Question 12

How many turns of the cycle are needed to make one hexose sugar?

Answer 12

• six
• 3 turns produces 6 triose phosphate molecules because two triose phosphate molecule are made for every CO2 molecule used
• 5/6 of the triose phosphate molecules are used to regernerate ribulose biphosphate
• therefore for 3 turns one triose phosphate molecule used to make hexose sugar
  
  • 2 triose phosphate molecule needed to form one hexose sugar
• needs 18 ATP and 12 reduced NADP