Final answer:
The suspension of isolated chloroplasts becomes alkaline due to the increase in proton concentration.
Step-by-step explanation:
The suspension of isolated chloroplasts becomes alkaline due to the increase in proton concentration.
In the process of photosynthesis, the chloroplast electron transport chain moves protons across the thylakoid membrane into the lumen. This leads to a high concentration of protons in the lumen, resulting in an alkaline environment.
The net result of the movement of protons is a low pH in the thylakoid lumen and a high pH in the stroma.