Q: When a primary lysosome fuses with a food vesicle to become a secondary lysosome: A: its pH drops via active pumping of protons into its interior. The explanation for the question says that the low pH is required in order to activate the digestive enzymes. I thought the lysosome normally has a pH around 5. Does the pH have to drop even further than that, or is 5 the pH that is required to activate the enzymes? If so, does it just float around with a neutral pH the rest of the time? Thanks.