1. 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