Two products of the light stage vital for the dark stage are NADPH and ATP. Which are they?

• A. NADPH and ADP
• B. NADPH and ATP
• C. NADP+ and ATP
• D. NADPH and NADP+

Answer: (B)

In the light-dependent stage, chloroplasts generate two key energy carriers that feed the dark stage: ATP and NADPH. ATP provides the chemical energy, produced when adenosine diphosphate (ADP) plus inorganic phosphate are joined by ATP synthase using a proton gradient. NADPH supplies reducing power, formed when NADP+ accepts electrons and a proton to become NADPH. The dark stage, or Calvin cycle, uses ATP for energy and NADPH as the source of electrons to convert carbon dioxide into sugars. The other options mix up what is produced versus what is consumed: ADP is a starting material used to make ATP, not a product; NADP+ is the oxidized form that accepts electrons to become NADPH, so it isn’t produced as such. Therefore, the correct pairing is NADPH and ATP.