Question

The cytoplasm of a cell is at ph7 and the interior of an organelle is ph8

A. What is the quantitative relationship between the number of hydrogen ions present at pH 7 versus pH 8?

B. Using your knowledge of transport in cells, what is a possible mechanism for how the cytoplasm would have a lower pH than inside the organelle?

Answer 1

A pH=-log(10)[H+], from this formula we can deduct that when the number of protons is higher the pH is lower and when the number of protons is lower the pH is higher. This means there are more hydrogen ions in the cytoplasm compared to the inside of an organelle.

B Hydrogen ions are very small particles so they can easily diffuse through the plasma membrane inside the cytoplasm, resulting in a higher number of protons and a lower pH. Organelle membranes have a lower permeability for hydrogen protons so the pH is higher.