Final answer:
NADPH is the product from light-dependent reactions used as a source of energy in light-independent reactions to help fix carbon dioxide into sugars in the Calvin cycle.
Step-by-step explanation:
The student's question is which product from the light-dependent reactions is used as a source of energy in the light-independent reactions. The correct answer is NADPH. In the light-dependent reactions of photosynthesis, energy from sunlight is harnessed by chlorophyll and other pigments, which results in the production of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate hydrogen). Both of these molecules are essential forms of chemical energy that the plant cell then uses during the light-independent reactions, also known as the Calvin cycle.
In the Calvin cycle, ATP provides the energy while NADPH provides the electrons required to fix carbon dioxide (CO2) into organic sugar molecules. Oxygen, which is also produced in the light-dependent reactions when water molecules are split, is not used in the Calvin cycle but is rather released as a byproduct into the atmosphere. Glucose and ADP (adenosine diphosphate) are not products of the light-dependent reactions.