Question

In an experiment, isolated chloroplasts placed in an illuminated solution with the appropriate chemicals can produce ATP synthesis. Predict what would happen to the synthesis rate if a compound is added to the solution that makes membranes freely permeable to hydrogen ions.

Short answer

Chloroplasts placed in an illuminated solution can decrease the rate of photosynthesis. The compound that is added to the solution does make the proton gradient. Without a proton gradient, ATP synthesis does not occur.

Step-by-step solution

Description of chloroplasts

Chloroplasts are the double-membrane organelles which consist of sub organelles such as stroma, grana, and thylakoids. The thylakoids are the region in which the photosynthesis process proceeds.

Description of chemiosmosis 

In plants, chemiosmosis is the process that occurs in chloroplasts as well as mitochondria. The protons are pumped from the electron transport chain that facilitates this process.

These protons are pumped outside the membrane. The ATP synthase draws this proton back into the chloroplasts for the phosphorylation of ADP into ATP.

Effect of adding a compound that makes the membrane permeable to the protons

The compound that makes the membrane freely permeable to hydrogen ions tends to make the membrane absorb the photons directly.There is no requirement for the proton gradient created by the proton pump. So, the uptake of hydrogen ions by the ATP synthase is hindered.

Hence, the compound added to the solution slows or hinders ATP production via the chemiosmosis mechanism.