TRANSPORT ACROSS CELL
MEMBRANES
Endocytosis and Exocytosis
Learning Outcomes
B9 - Describe the structure and function of
the cell membrane:
 Describe and compare endocytosis and exocytosis
in terms of:
Method of transport (use of vesicles)
 Use of energy (active vs. passive)
 Type / size of molecule transported

Enodcytosis and Exocytosis
Exocytosis and Endocytosis
 vesicles move substances in and out of cells
 vesicles can fuse with the cell membrane (where
might they be coming from?)
 new vesicles or vacuoles can be formed from the cell
membrane
 Active (requires ATP for energy)
Exocytosis
 Vesicle inside the cell fuses with the cell
membrane (and becomes part of the
membrane)
 Contents are released to the outside
 Ex. Secretion of proteins from Golgi (ex. insulin,
enzymes), secretion of waste products
Endocytosis
 Takes substances into the cell
 Plasma membrane forms a vesicle around a
substance and takes it in
 (Note that part of the plasma membrane becomes
the vacuole)
 Pinocytosis (“cell drinking”) - liquid or small
particles taken in by tiny vesicles
 Phagocytosis (“cell eating”) – entire cells or large
food particles are taken in - ex. white blood cells take
in bacterial cells, which are then destroyed by
lysosomes
White blood cell phagocytizing bacteria
Receptor Mediated Endocytosis
 the particle being taken in first binds to a
specific receptor protein on the outside of the
cell membrane
Organelles and Membrane Working
Together