Question

The creation of proton gradient across thylakoid membrane is a result of
A. Decrease in proton number in stroma
B. Decrease in pH number in the lumen
C. Accumulation of protons in the lumen
D. All of the above

Answer 1

Hint:Within the mitochondrial membrane, a high-energy electron is passed along an electron transport chain. The energy released pumps hydrogen out of the vacuum of the matrix. The gradient created by this pushes hydrogen back through the membrane, through ATP synthase. When this occurs, ATP synthase synthesizes ATP from ADP by the action of enzymes.

Complete Answer:
Pigments of light-harvesting complex channel light energy to PSII and PSI in chloroplasts. Light energy is used to separate the electron from the PSII, beginning the progression through the electron transport chain.
As electrons travel through the photosystems, protons are transferred through the membrane. This is because the primary receptor of the electron, which is situated on the outer side of the membrane, passes the electron not to an electron transporter, but to a H transporter. This molecule extracts the proton from the stroma when transmitting the electron. While this molecule transfers on the electron to the electron carrier on the inside of the membrane, the proton is emitted on the inside or on the lumen side of the membrane. The NADP reductase enzyme is found on the stroma side of the membrane. Along with electrons coming from the PS I acceptor, protons are required to reduce NADP+ to NADPH H+. These protons are supplied from the stroma. Thus, within the chloroplast, the number of protons in the stroma decreases, while the number of protons increases in the lumen. This induces a proton gradient through the thylakoid membrane, as well as an observable decline in pH in the lumen.

Thus, the correct answer is option ‘D’ i.e., All of the above.

Note: During the transport of electrons, the participating protein complexes push the protons out of the matrix into the intermembrane space. This produces a concentration gradient of protons that is used by another protein complex called ATP synthase to produce the synthesis of the ATP energy carrier molecule.