Final answer:
In Phase 2 of the Calvin cycle, 3-PGA is reduced to G3P using the energy from ATP and electrons from NADPH, without the addition or removal of carbon atoms. The number of carbon atoms in G3P is the same as in 3-PGA.
Step-by-step explanation:
The statement that there is no addition or removal of carbon atoms during the reduction of 3-phosphoglycerate (3-PGA) to glyceraldehyde 3-phosphate (G3P) in Phase 2 of the Calvin cycle is indeed true. During this phase, each 3-PGA molecule receives additional electrons through a reduction reaction, using both ATP and NADPH generated from the light-dependent reactions of photosynthesis. This conversion does not add or remove carbon atoms; rather, it transforms the molecular structure by adding energy and reducing power in the form of electrons and hydrogen ions. Hence, the number of carbon atoms in G3P remains the same as in 3-PGA.
The process involves the transformation of six molecules of 3-PGA into six molecules of G3P. This reaction is catalyzed by enzymes and requires the input of energy and reduction equivalents from ATP and NADPH, which after the reaction, are converted into ADP and NADP+, respectively. These latter molecules return to the light reactions to be recharged. Additionally, this step in the Calvin cycle is crucial for the eventual production of carbohydrates, as G3P can serve as a building block for larger sugar molecules.