Question

Identify the electron donor for the electron transport chain in photosynthesis. $$$$
A. Oxygen
B. $NADP{H_2}$
C. $NAD{P^ + }$
D. Water

Answer 1

Plants do photosynthesis at a very slow rate in the night. They need sunlight to make their food. Conversion of sunlight to chemical energy needs electrons, ATP, NADPH, etc. they run through a cascade to produce Carbon dioxide, water, and energy. The various cycles for energy oxidation were discovered by Melvin Calvin.

Complete answer:
Photosynthesis is the process of making plant food in the presence of sunlight. This process occurs in the chlorophyll in the plastids. The photosynthesis process is done by absorbing the sunlight and converting it into chemical energy.
The process needs light to occur. It has two photosystems- light reaction and dark reaction. Dark reaction is named so as it does not require light for its working. But it does not mean it occurs at night as it just needs the products from the light reaction to occur. So both the processes occur in the daytime.
In the dark reaction, carbon dioxide is reduced to carbohydrates. It occurs in three steps- carbon fixation, reduction, and regeneration. The Calvin cycle in stroma occurs in the presence of light and the products are used in the dark reaction. This reaction occurs outside the thylakoids. The products are sugar molecules and other organic molecules that are used for the cell to function.
In the light-dependent reaction, the NADP is reduced to $NADP{H_2}$. Thus it becomes the terminal acceptor of an electron in the light-dependent reaction.
The $NADP{H_2}$ will donate the electrons to the dark reaction. It will be reduced back to the NADP by reducing 3- Phosphoglyceric acid to Glyceraldehyde- 3- Phosphate.
Option A: Oxygen: It is produced at the last as a product.
Option B: $NADP{H_2}$: This will form the donor of an electron in the dark reaction in photosynthesis.
Option C: $NAD{P^ + }$: It is oxidized in the light reaction to $NADP{H_2}$.
Option D: Water: It is the initial requirement and also the by-product.
So the answer is option B: $NADP{H_2}$

Note: Electron transport chain does the redox reactions to transfer electrons from donors to acceptors. The electrons are passed from the membrane. There are 4 complexes used in the chain are NADH-Q, succinate-Q- reductase, Complex 3 and Complex 4 (cytochrome c oxidase).