Question

Plants require water for transpiration, metabolism, and photosynthesis. How is water used in photosynthesis?

A. as a substrate for ATP synthase
B. as an electron acceptor
C. to combine with ADP forming ATP
D. to combine with NADP+ to form NADPH
E. as an electron donor

Answer 1

In photosynthesis, water acts as an electron donor, providing electrons that are essential for the production of NADPH in the light-dependent reactions, which is subsequently used in the Calvin cycle to form carbohydrates.

Step-by-step explanation:

In photosynthesis, water is used as an electron donor. This process begins in the photosystem II reaction center, where energy from sunlight extracts electrons from water molecules.

These electrons are then transferred through the chloroplast electron transport chain to photosystem I, where they reduce NADP+ to NADPH.

This creation of NADPH is crucial for the Calvin cycle, where it is utilized along with ATP to convert carbon into carbohydrates such as glucose. Therefore, option E 'as an electron donor' correctly describes how water is used in photosynthesis.