Q1 / 56 · IAT (IISER) 2026 · Biology
Which of the following processes result in development of a proton gradient across the thylakoid membrane during photosynthesis?
i. Release of protons into the lumen of the thylakoid by plastoquinone
ii. Consumption of protons in the stroma during the reduction of $\text{NADP}^+$
iii. Release of protons into the lumen of the thylakoid by ATP synthase
iv. Release of protons into the lumen of the thylakoid by water splitting reaction
i. Release of protons into the lumen of the thylakoid by plastoquinone
ii. Consumption of protons in the stroma during the reduction of $\text{NADP}^+$
iii. Release of protons into the lumen of the thylakoid by ATP synthase
iv. Release of protons into the lumen of the thylakoid by water splitting reaction
- Correct answerAi, ii and iv
- Bi, ii and iii
- Cii, iii and iv
- Di, iii and iv
Solution
During photosynthesis, the proton gradient across the thylakoid membrane is developed due to the following processes:
Plastoquinone acts as a hydrogen carrier, transferring electrons from PSII to the cytochrome $b_6f$ complex while simultaneously pumping protons from the stroma into the thylakoid lumen. This increases the proton concentration in the lumen.
The enzyme $\text{NADP}$ reductase is located on the stroma side of the membrane. The reduction of $\text{NADP}^+$ to NADPH consumes protons from the stroma, which decreases the proton concentration in the stroma.
The water splitting reaction (photolysis) occurs on the inner side of the thylakoid membrane, releasing protons directly into the lumen, further increasing the proton concentration there.
ATP synthase facilitates the movement of protons from the lumen back to the stroma to synthesize ATP. This process dissipates the proton gradient rather than developing it.
Therefore, processes i, ii, and iv are responsible for the development of the proton gradient.
Answer: i, ii and iv
Plastoquinone acts as a hydrogen carrier, transferring electrons from PSII to the cytochrome $b_6f$ complex while simultaneously pumping protons from the stroma into the thylakoid lumen. This increases the proton concentration in the lumen.
The enzyme $\text{NADP}$ reductase is located on the stroma side of the membrane. The reduction of $\text{NADP}^+$ to NADPH consumes protons from the stroma, which decreases the proton concentration in the stroma.
The water splitting reaction (photolysis) occurs on the inner side of the thylakoid membrane, releasing protons directly into the lumen, further increasing the proton concentration there.
ATP synthase facilitates the movement of protons from the lumen back to the stroma to synthesize ATP. This process dissipates the proton gradient rather than developing it.
Therefore, processes i, ii, and iv are responsible for the development of the proton gradient.
Answer: i, ii and iv
Hence, the correct answer is option: 'A'.