During the Calvin cycle, what happens during the carbon fixation phase?

A. RuBP (ribulose bisphosphate) is regenerated.

B. G3P is produced.

C. NADPH is produced.

D. The Calvin cycle incorporates each CO₂ molecule, one at a time, by attaching it to a five-carbon sugar named ribulose bisphosphate.

E. Molecular oxygen is produced.

F. ATP is produced.

In the carbon fixation phase of the Calvin cycle, carbon dioxide is incorporated into ribulose bisphosphate (RuBP) by the enzyme RuBisCO, producing 3-phosphoglycerate (3-PGA). This process is essential for converting inorganic carbon into organic compounds that can eventually lead to glucose formation. Ultimately, this step is vital for sustaining the photosynthetic process in plants.

Explanation:

Understanding Carbon Fixation in the Calvin Cycle

During the Calvin cycle, the carbon fixation phase is crucial as it converts inorganic CO2 into an organic form. This process begins when the enzyme RuBisCO catalyzes the reaction between carbon dioxide and ribulose bisphosphate (RuBP), leading to the production of a three-carbon compound called 3-phosphoglycerate (3-PGA).

Process of Carbon Fixation

Specifically, during carbon fixation:

The enzyme RuBisCO incorporates each CO2 molecule into RuBP, creating 3-PGA.
This process occurs one CO2 molecule at a time, requiring the cycle to turn six times to produce the six-carbon sugar glucose.

As such, carbon fixation is where the carbon atoms from CO2 become part of an organic molecule framework, paving the way for the subsequent stages of the Calvin cycle.

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