We will see in Chapter 15 that endosomes, which are membrane-enclosed intracellular organelles, need an acidic lumen in order to function. Acidification is achieved by an $\mathrm{H}^{+}$ pump in the endosomal membrane, which also contains $\mathrm{Cl}^{-}$ channels. If the channels do not function properly (e.g., because of a mutation in the genes encoding the channel proteins), acidification is also impaired.
A. Can you explain how Cl' channels might help acidification?
B. According to your explanation, would the Cl- channels be absolutely required to lower the pH inside the endosome?