Question

Identify the electron donor for the electron transport chain in photosynthesis.

• A. Oxygen
• B. NADPH${}_2$
• C. NADP${}^{+}$
• D. Water

Answer 1

Answer: (B)

NADPH${}_2$

Photosynthesis takes place in two steps, viz; Light-dependent reaction/Light reaction and Light independent reaction/Calvin cycle/ Dark reaction.

1. During the process of Light-dependent reaction, the NADP is reduced to NADPH${}_2$ by accepting an electron from PS1. Thus becoming terminal acceptor of the electron in Light reaction. This NADPH${}_2$ is used in the dark reaction.
2. During the process of Dark reaction, this NADPH${}_2$ fuels the reaction by donating the electron. It is oxidized back to NADP by reducing 3-Phosphoglyceric acid to Glyceraldehyde-3-phosphate.

Thus NADPH${}_2$ is an electron donor in photosynthesis.