Final answer:
The compounds ATP and NADPH are used to convert PGA into glyceraldehyde 3-phosphate (G3P) through a reduction reaction in photosynthesis.
Step-by-step explanation:
The high energy compounds ATP and NADPH are used to convert PGA into molecules of glyceraldehyde 3-phosphate (G3P). This process is known as a reduction reaction because it involves the gain of electrons by 3-PGA, which is the definition of reduction. The ATP provides the energy by losing its terminal phosphate atom, transforming into ADP, while NADPH loses both energy and a hydrogen atom, turning into NADP+. Both molecules, ADP and NADP+, then cycle back to the light-dependent reactions to be recharged with energy.