1. Structure and Function
Cell Membranes
Structure and Function

2. Animal Cell Membrane

3. Semi-permeable Membranes
Lipid membranes are semi-permeable, also called selectively permeable
Water moves across the membrane freely
Ions (charged particles) do not move across the membrane freely
Many large molecules do not move across the membrane freely

4. Passive Transport
Diffusion – the movement of substances from an area of higher concentration to an area of lower concentration
Osmosis – the movement of water from an area of higher water content to an area of lower water content

5. Active Transport
The movement of a substance against the concentration gradient (from lower concentration to higher concentration
Active transport requires the use of energy

6. Membrane proteins play an important role in passive and active transport

7. Very large molecules may be taken in by endocytosis

8. Exocytosis secretes substances