1. Maintaining Homeostasis
Cell Membrane
Maintaining Homeostasis

2. Function
Controls the movement of substances across the cell membrane.

3. (b) Structure of the plasma membrane
Lipid bilayer
Phospholipids
Polar heads face out to the external cell environment and to the internal cytoplasm.
Lipid tails face each other
Outside of cell
Inside of cell
Hydrophilic
region
Hydrophobic
(b) Structure of the plasma membrane
Phospholipid
Proteins
TEM of a plasma
membrane. The
plasma membrane,
here in a red blood
cell, appears as a
pair of dark bands
separated by a
light band.
(a)
0.1 µm

4. Imbedded Proteins 4 Types Carbohydrate tags identify the cell
Receptors signal changes to the cell
Enzymes assist in chemical reactions
Transport proteins move substances through the cell membrane

5. Passive Transport
Diffusion moving substances from areas of high concentration to low concentration
Osmosis moving water from a dilute concentration to a high concentration
Requires no energy

6. Active Transport Protein Pumps – move molecules through the membrane
Endocytosis – carries substances into the cell in vessicles
Exocytosis – carries substances out of the cell in vessicles
Requires energy