Energy Transfers in and Between Organisms: Photosynthesis - Light-Independent Reactions

Question 1

What is the light-independent reaction also known as?

Answer 1

• The Calvin cycle

Question 2

Where does the light-independent reaction occur?

Answer 2

• Stroma of chloroplasts

Question 3

What are the products of the Calvin cycle?

Answer 3

• Triose phosphate

- Ribulose bisphosphate (5-carbon compound)

Question 4

What are the main stages of the Calvin cycle?

Answer 4

• Formation of glycerate 3-phosphate
• Formation of triose phosphate
• Regeneration of ribulose bisphosphate

Question 5

Draw the Calvin cycle

Answer 5

Question 6

What happens during the formation of glycerate 3-phosphate?

Answer 6

• Carbon dioxide diffuses into the stroma of the chloroplast
• CO2 reacts with ribulose bisphosphate (RuBP) to form an unstable 6-carbon compound
• This reaction is catalysed by enzyme rubisco
• This unstable compound quickly breaks down into two molecules of a 3-carbon compound called glycerate 3-phosphate (GP)

Question 7

What happens during the formation of triose phosphate?

Answer 7

• 2 Glycerate 3-phosphates (GP) are reduced to 2 triose phosphates (TP)
• 2NADPH is recycled to 2NADP, by giving away an electron each - requires H+ ions
• 2ATP are hydrolysed
• 1/6 TP is converted into organic substances (e.g glucose) and 5/6 continues in Calvin cycle to regenerate RuBP

Question 8

Where does the energy used to reduce GP into TP come from?

Answer 8

• 2ATP from light-dependent reaction are hydrolysed to reduce 2GPs into 2TPs

Question 9

Where do the H+ ions used to turn NADPH to NADP come from?

Answer 9

• Comes from photolysis in the light-dependent reaction

Question 10

What happens during the regeneration of ribulose bisphosphate?

Answer 10

• 5/6 molecules of TP produced in cycle are used to regenerate RuBP
• 2 TP molecules needed to produce 1 RuBP (5C) and another useful organic compound (1C)
• 1 ATP is hydrolysed for every RuBP molecule made