Question

Ribulose biphosphate (RuBP), the molecule that CO₂ is attached to (fixed) in the cycle must continually _________.

1) be regenerated
2) be broken down
3) be converted to glucose
4) be released into the atmosphere

Answer 1

RuBP must continually be regenerated for the Calvin cycle to sustain photosynthesis, allowing more CO₂ to be fixed. This regeneration uses additional ATP and involves the conversion of glyceraldehyde-3-phosphate (G3P) back into RuBP.

Step-by-step explanation:

In the process of photosynthesis, Ribulose biphosphate (RuBP) must continually be regenerated. This regeneration is critical for the Calvin cycle to continue functioning, allowing for more CO₂ to be fixed. During the Calvin cycle, RuBP is combined with CO₂ in a reaction catalyzed by the enzyme RuBisCO, resulting in the formation of 3-phosphoglycerate (3-PGA). Subsequently, ATP and NADPH are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), from which glucose is synthesized. The excess G3P molecules that are not used in glucose production are involved in the regeneration of RuBP, consuming additional ATP in the process. This continuous regeneration is essential for photosynthesis to sustain a continuous intake and fixation of CO₂.