Lysosomes contain digestive enzymes, originating in part from the Golgi apparatus are organelles called lysosomes. They contain digestive enzymes, and they are the sites where macromolecules proteins, polysaccharides, nucleic acids, and lipids—are hydrolyzed into their monomers. Lysosomes are about 1 μm in diameter, are surrounded by a single membrane, and have a densely staining, featureless interior. There may be dozens of lysosomes in a cell, depending on its needs.
Lysosomes are sites for the breakdown of food and foreign objects taken up by the cell. These materials get into the cell by a process called phagocytosis (phago-, “eating”; cytosis, “cellular”), in which a pocket forms in the plasma membrane and eventually deepens and encloses material from outside the cell. This pocket becomes a small vesicle that breaks free of the plasma membrane to move into the cytoplasm as a phagosome containing food or other material. The phagosome fuses with a primary lysosome, forming a secondary lysosome where digestion occurs.