Question

Primary acceptor of $C{ O }_{ 2 }$ in photosynthesis is
(a)Phosphoric acid
(b)Ribulose phosphate
(c)Glucose
(d)Ribulose-1,5- biphosphate

Answer 1

Hint: The primary acceptor of carbon dioxide is an important five-carbon enzyme in the Calvin cycle and helps in carbon fixation. Magnesium ion is essential for its enzymatic activity.

Complete answer:
Ribulose-1,5- biphosphate is one of the enzymes used in the Calvin cycle. Ribulose-1,5- biphosphate helps in fixation of carbon dioxide where:
Carbon dioxide reacts with Ribulose-1,5- biphosphate to form two 3-phosphoglycerate. This reaction is highly exergonic. The reaction is catalyzed by the Ribulose-1,5- biphosphate carboxylase/ oxygenase (rubisco). Rubisco is a soluble enzyme located on the stromal surface of the thylakoid membrane of chloroplasts.

Additional Information:
-In the stroma, in addition to carbon dioxide, two other components are present to initiate the light-independent reactions: an enzyme called ribulose bisphosphate carboxylase (RUBISCO) and three molecules of ribulose bisphosphate (RUBP).
-Calvin cycle occurs in all photosynthetic plants during the dark phase of photosynthesis where it stores the ATP energy during the light reaction in the carbohydrate molecule as the food energy.

So, the correct answer is, ‘Ribulose-1,5- biphosphate.’

Note: -The Calvin cycle was first observed by Melvin Calvin in Chlorella and he was awarded a Nobel prize for this work.
-This cycle involves the main three stages: fixation, reduction, and regeneration.
-Calvin cycle is also known as the dark reaction or ${ C }_{ 3 }$ cycle or reductive pentose phosphate cycle and photosynthetic carbon reduction cycle (PCR).