Multiple choice

The first event in the Calvin cycle is the attachment of carbon dioxide to the five carbon RuBP molecule, which ____________.

  1. forms a six carbon molecule that immediately breaks down into two three carbon PGA molecules

  2. is a reaction assisted by large quantities of RuBP carboxylase enzyme

  3. decreases cell carbon dioxide levels that increases the diffusion gradient

  4. 1, 2 and 3 are correct

  5. immediately becomes a six carbon sugar that is the base for starch, sucrose, cellulose, etc.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The Calvin cycle begins with CO2 fixation by RuBP carboxylase (Rubisco), forming an unstable 6-carbon intermediate that splits into two 3-carbon PGA molecules. This reaction is enzyme-assisted and helps maintain the diffusion gradient for CO2 uptake.

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