Question

What is the primary role of water in the "Z-scheme" of oxygenic photosynthesis?

A) Water acts as an electron acceptor.
B) Water serves as an electron donor for Photosystem I.
C) Water provides carbon dioxide for the Calvin cycle.
D) Water generates NADPH in Photosystem II.

Answer 1

Water's primary role in the Z-scheme of oxygenic photosynthesis is as an electron donor for PSII, where it is split to replace electrons, produce ATP, and release oxygen as a byproduct.

Step-by-step explanation:

The primary role of water in the "Z-scheme" of oxygenic photosynthesis is to serve as an electron donor for Photosystem II (PSII). In this process, the splitting of water molecules occurs at PSII, where the reaction center called P680 loses an electron to the primary electron acceptor. This missing electron is then replaced by a low-energy electron from water, which results in the water molecule being split into oxygen, hydrogen ions, and electrons. These electrons are then used to re-reduce P680. The hydrogen ions contribute to the electrochemical gradient used for synthesizing ATP, while the oxygen is released as a byproduct and eventually part of it escapes to the atmosphere.