Question

Based on your understanding of the function of the chloroplasts, why doesturning on the light cause the pH in the solution outside the thylakoids toincrease?

Answer 1

Based on your understanding of the function of the chloroplasts, why doesturning on the light cause the pH in the solution outside the thylakoids toincrease?

A. Photoexcitation of chlorophyll caused ATP synthase to pump H+.

B. Calvin cycle produced numerous H+.

C. Illumination of chlorophyll causes electrons to flow into stroma of chloroplast.

D. Electron transfer along electron transport chain resulted in pumping of H+ from stroma to inside the thylakoid.

Answer:

D. Electron transfer along electron transport chain resulted in pumping of H+ from stroma to inside the thylakoid.

Explanation:

As chlorophyll pigments present in the thylakoid membranes of chloroplast absorb light, the transfer of electrons from the reaction center of PSII towards the electron transport chain occurs. This electron transfer also pumps some protons from stroma to the thylakoid lumen making the inside of the lumen more acidic while stroma becomes alkaline in nature. This proton concentration gradient is used to drive the process of ATP synthesis. This is why exposure to light makes the outside of thylakoids to have a higher pH.