Question

From the diagram given below which represents the Calvin cycle, name the molecules A and B.

• A. 3-phosphoglycerate - A,
  triose phosphate - B
• B. Triose phosphate - A,
  3-phosphoglycerate - B
• C. Triose phosphate -A, glucose - B
• D. Glucose - A,
  3-phosphoglycerate - B

Answer 1

The correct option is A 3-phosphoglycerate - A,

triose phosphate - B
The diagram represents Calvin cycle. All the reactions that occur during the synthesis of glucose were given in detail by Calvin. Hence it is also called Calvin cycle. The Calvin cycle includes three stages - carboxylation, reduction and regeneration.

During carboxylation or carbon dioxide fixation, RuBP (ribulose-1,5-bisphosphate) combines with carbon dioxide and forms into an unstable 6 carbon compound. The 6 carbon compound splits into two molecules of 3-PGA. Hence, molecule A is 3-phosphoglycerate (3-PGA).

Carboxylation is followed by reduction in which 3-PGA is reduced with the help of ATP and NADPH to form triose phosphate. Hence, molecule B is triose phosphate.

Triose phosphate is recycled to regenerate RuBP, the primary acceptor of carbon dioxide. Triose phosphate is also utilised in the synthesis of glucose.