Which molecule produced in the light-dependent stage carries reducing power to the dark reactions?

Which molecule produced in the light-dependent stage carries reducing power to the dark reactions?

• A. NADH
• B. ATP
• C. Oxygen
• D. NADPH carries reducing power to the dark stage

Answer: (D)

The key idea is that reducing power—electrons and hydrogen used to reduce carbon compounds in the Calvin cycle—comes from NADPH. In the light-dependent reactions, light energy drives the transfer of electrons to NADP+, producing NADPH. This molecule then travels to the stroma and donates its electrons to the carbon-fixing steps, providing the reducing equivalents needed to convert carbon dioxide into sugars. ATP is also produced in the light reactions to supply energy for these steps, but it does not carry reducing power. Oxygen is released as a by-product of water splitting, not used as a reducing carrier. So, the molecule that carries the reducing power to the dark reactions is NADPH.

The key idea is that reducing power—electrons and hydrogen used to reduce carbon compounds in the Calvin cycle—comes from NADPH. In the light-dependent reactions, light energy drives the transfer of electrons to NADP+, producing NADPH. This molecule then travels to the stroma and donates its electrons to the carbon-fixing steps, providing the reducing equivalents needed to convert carbon dioxide into sugars. ATP is also produced in the light reactions to supply energy for these steps, but it does not carry reducing power. Oxygen is released as a by-product of water splitting, not used as a reducing carrier. So, the molecule that carries the reducing power to the dark reactions is NADPH.