Final answer:
ATP-dependent proton pumps establish the low pH of lysosomes, creating an acidic environment that is necessary for the activity of acid hydrolases.
Step-by-step explanation:
The low pH of lysosomes is established by ATP-dependent proton pumps. These proton pumps are located in the lysosome membrane and pump protons into the lumen of the lysosome, creating an acidic environment. The acidic environment is necessary for the activity of the acid hydrolases, which are the enzymes responsible for breaking down various molecules within the lysosome.