11.4 Bulk Transport

Figure 11.20: Phagocytosis by a Phagocyte

Phagocytosis (from the Greek word phagein [meaning “to eat”] and cytos [meaning “cell”]) refers to the uptake of an organism or some other fragment of organic matter (see figure 11.20).

Pinocytosis (from the Greek word pinein [meaning “to drink”]) refers to the intake of liquid.

In receptor-mediated endocytosis, molecules first bind to specific receptors in the plasma membrane. These molecules have a conformation that snugly fits into the receptor.

11.4.1 Exocytosis

Figure 11.21: Exocytosis in a Cell

Exocytosis (see figure 11.21) is the reverse of endocytosis - it is the discharge of material from vesicles at the cell surface.

In figure 11.21, proteins and other molecules are secreted from cells in small packets called vesicles. The vesicles fuse with the plasma membrane and release their contents outside the cell (like mentioned previously).