Which stage of photosynthesis requires ATP and NADPH?

The light-independent reactions, also known as the Calvin cycle, are the stage of photosynthesis that specifically requires ATP and NADPH. During this stage, the energy stored in ATP and the reducing power of NADPH, both produced during the light-dependent reactions, are used to convert carbon dioxide into glucose.

In the Calvin cycle, ATP provides the necessary energy to drive the reactions, while NADPH supplies the electrons needed for reducing 3-phosphoglycerate into glyceraldehyde-3-phosphate, which ultimately leads to the formation of glucose and other carbohydrates. This interdependence on the products of the light-dependent reactions highlights the integrated nature of photosynthesis.

The other stages mentioned, such as the light-dependent reactions, primarily focus on the capture of light energy and the production of ATP and NADPH, while photolysis refers specifically to the splitting of water molecules during the light-dependent reactions to release oxygen. Transpiration involves the movement of water through plants and is not directly related to the photosynthetic process itself. Hence, the focus on ATP and NADPH distinctly marks the light-independent reactions as the correct choice.