Question

From which component of the light-dependent reactions does NADPH form most directly?
a. photosystem II
b. photosystem I
c. cytochrome complex
d. ATP synthase

Short answer

PSI is the molecule closest to NADP+ and the last to transfer electrons to it. As a result, option (b) Photosystem I is the correct response.

Step-by-step solution

step-1: Introduction

At PSII, a water molecule is broken down, releasing two electrons that move to PSI via the cytochrome complex. At PSI, photons are absorbed, causing electrons to be excited again and sent to NADP+ in the stroma (dark process) to be converted/reduced into NADPH.

step-2: Explanation of correct answer

Option (b) Photosystem I is the correct answer.

Because it is at the end of the "Z" scheme of the light-dependent non-cyclic process, Photosystem I is more directly related with the reduction of NADP+ to NADPH. As a result, option is the proper response (b).

step-3: Explanation of incorrect answers

Photosystem II (option a). Although Photosystem II is involved in the reduction of water molecules, it is not the most important component in the conversion of NADP+ to NADPH. As a result, this is a bad choice.

Cytochrome complex (option c). The electrons are transferred from PSII to PSI via the cytochrome complex. As a result, this is a bad choice.

ATP is option (d). Because it is engaged in ATP synthesis by proton motive force in the thylakoid membrane, ATP synthase is not directly related to NADP+ reduction to NADPH. As a result, this is a bad choice.