Question

Can ribulose bisphosphate (RuBP) combine with both carbon dioxide and oxygen gas?

Answer 1

Hint: The Calvin cycle is a process that plants and algae use to convert carbon dioxide from the air into sugar on which the autotrophs need to grow. It is a light-independent process. The Calvin cycle has four major steps: carbon fixation, reduction phase, carbohydrate formation, and regeneration phase.

Complete answer:
To solve this question, we must know about the process of the Calvin cycle. Calvin cycle is one of the most important processes on which all living beings depend. It is the main source of energy and food. The Calvin cycle has four steps.

A $CO_2$ molecule combines with a five-carbon acceptor molecule called ribulose-1,5-bisphosphate (RuBP). This step makes a six-carbon compound that splits into two molecules of a three-carbon compound i.e 3-phosphoglyceric acid (3-PGA). Enzyme RuBP carboxylase/oxygenase also known as rubisco acts as a catalyst.

In the second stage, ATP and NADPH are used to convert the 3-PGA molecules into molecules of a three-carbon sugar i.e glyceraldehyde-3-phosphate. Some G3P molecules go to make glucose, while others must be recycled to regenerate the initial RuBP acceptor.

Thus, the enzyme Rubisco not only initiates carbon fixation in the Calvin cycle but it also combines with oxygen to initiate photo-respiration.

Additional Information: 3 ADP and 2 NADP+ are obtained during Calvin cycle. These are utilised in the light reaction.

Note: RuBP stands for ribulose bisphosphate and it's a 5-carbon compound involved in the Calvin cycle, which is part of the light-independent reactions of photosynthesis. Note that the active site of rubisco cannot distinguish the two similar substrates: O=C=O and O=O.