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.
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.