Lysomes are membrane-bound vesicles that contain hydrolytic enzymes involved in intracellular digestion. These enzymes operate at a pH of 5 and therefore need to be enclosed within the lysosomoe - an acidic enviornment distinct from the neutral pH of the cytosol. Lysomes fuse with the endocytotic vacules, thereby breaking down the material ingested by the cell. Lysosomes also aid in renewing a cell's own components by breaking down the old ones and releasing their molecular building blocks into the cytosol for reuse.