1. Cell Structure
4A - Membranes

2. unit membrane a thin structure composed of proteins and lipids
type of membrane found around all cells
around many of the structures inside cells
the outer boundary of a cell

3. Important Property of Membranes
selectively permeable: certain molecules go through them and other molecules do not

4. Selectively Permeable
Not all membranes are permeable to the same molecules.
However water, oxygen, and carbon dioxide are small and easily passes through most membranes.

5. How does a substance pass through a unit membrane?
Passive Transport
Active Transport

6. PASSIVE TRANSPORT
the passage of substances across a membrane without the use of energy
This is the main way.

7. two main forms of passive transport
Diffusion
Osmosis

8. diffusion
the movement of molecules from an area of higher concentration to an area of lower concentration

9. diffusion
diffusion can be speeded up by such things as heat,movement, and pressure

10. the diffusion of water through a membrane
osmosis
the diffusion of water through a membrane

11. ACTIVE TRANSPORT
the passage of particles through a membrane; requires the use of cellular energy
(sometimes because of the size of the molecule being so large, or going against gradient)