Which stage uses light energy to synthesize ATP and NADPH?

Which stage uses light energy to synthesize ATP and NADPH?

• A. Dark stage
• B. Light dependent stage
• C. Oxygen-evolving stage
• D. Calvin cycle

Answer: (B)

The main idea here is that light energy powers the production of chemical energy carriers during the light-dependent reactions. In this stage, chlorophyll absorbs light and drives electrons through an electron transport chain in the thylakoid membranes. As the electrons flow, a proton gradient is built up and ATP synthase uses that gradient to make ATP. The electrons are also transferred to NADP+, forming NADPH. So this stage converts light energy directly into ATP and NADPH, which are then used in the next stage to build sugars. The other options don’t fit this role. The term often called the dark stage refers to the part that uses ATP and NADPH to fix carbon (the Calvin cycle) rather than producing them with light. The oxygen-evolving portion is part of the light reactions that splits water to release oxygen, but the overall synthesis of ATP and NADPH is driven by the light-dependent stage. The Calvin cycle consumes ATP and NADPH rather than producing them.

The main idea here is that light energy powers the production of chemical energy carriers during the light-dependent reactions. In this stage, chlorophyll absorbs light and drives electrons through an electron transport chain in the thylakoid membranes. As the electrons flow, a proton gradient is built up and ATP synthase uses that gradient to make ATP. The electrons are also transferred to NADP+, forming NADPH. So this stage converts light energy directly into ATP and NADPH, which are then used in the next stage to build sugars.

The other options don’t fit this role. The term often called the dark stage refers to the part that uses ATP and NADPH to fix carbon (the Calvin cycle) rather than producing them with light. The oxygen-evolving portion is part of the light reactions that splits water to release oxygen, but the overall synthesis of ATP and NADPH is driven by the light-dependent stage. The Calvin cycle consumes ATP and NADPH rather than producing them.