Why is the Calvin cycle also known as C3 photosynthesis?

A) It involves three stages: Carbon fixation, Reduction, and Regeneration of RuBP
B) It produces three molecules of G3P in each cycle
C) It utilizes three types of pigments during light absorption
D) It is the third stage in the process of photosynthesis

The Calvin cycle is known as C3 photosynthesis because the first stable product of the cycle is a 3-carbon sugar molecule, GA3P. The cycle consists of three stages: fixation, reduction, and regeneration, and it must occur three times to release one GA3P molecule.

Explanation:

The Calvin cycle is also known as C3 photosynthesis because the first stable product formed during the cycle is a 3-carbon sugar called glycerate 3-phosphate (3-PGA). It is named after the number of carbon atoms in the molecules that are involved in the cycle. The Calvin cycle is organized into three basic stages: fixation, reduction, and regeneration.

Fixation - Carbon dioxide (CO2) is attached to a five-carbon sugar named ribulose bisphosphate (RuBP) by the enzyme RuBisCO. This reaction forms two 3-PGA molecules.
Reduction - ATP and NADPH are used to convert the 3-PGA into a different 3-carbon molecule called glyceraldehyde 3-phosphate (GA3P).
Regeneration - Most of the GA3P produced is used to regenerate RuBP, enabling the cycle to continue. Only a small amount of GA3P leaves the cycle to contribute to the formation of other compounds, like glucose. For one molecule of GA3P to exit the cycle, the process must occur three times.

Since the GA3P molecule contains three carbon atoms, and it is the first stable product of photosynthesis, this process is referred to as C3 photosynthesis.