Ammonia (NH₃) is a weak base that under acidic conditions becomes protonated to the ammonium ion in the following reaction:

NH₃ + H⁺ → NH4⁺

NH₃ freely permeates biological membranes, including those of lysosomes. The lysosome is a sub-cellular organelle with a pH of about 4.5-5.0; the pH of cytoplasm is - 7.0. What is the effect on the pH of the fluid content of lysosomes when cells are exposed to ammonia? Protonated ammonia does not diffuse freely across membranes.