Final answer:
To synthesize 2 G3P molecules, 4 NADPH are required. This is derived from the larger process where typically 6 NADPH are used to create 6 G3P, of which 2 are used to synthesize G3P with 2 being part of the regeneration process of the cycle.
Step-by-step explanation:
To synthesize 2 molecules of glyceraldehyde 3-phosphate (G3P), a total of 4 NADPH are needed. This calculation is based on the information that converting 6 molecules of 3-phosphoglyceric acid (3-PGA) into 6 molecules of G3P requires 6 molecules of NADPH. Since the synthesis of 1 G3P molecule requires 1 NADPH, synthesizing 2 G3P molecules would naturally require 2 NADPH. But because initially we produce 6 G3P to turn into 2 G3P and regenerate more of the initial reactant (RUBP), we need 6 NADPH which get split into two groups: 4 for G3P synthesis and 2 for regeneration processes. Ultimately, the photosynthesis process is highly efficient in its use of ATP and NADPH to produce sugars like glucose, serving as a vital energy source for plants.