1. Cell membranes and exchange of material
HBS 3A

2. Exchange of material Occurs at the cell membrane
Involves the intake of essential materials eg nutrients and oxygen and the removal of unwanted materials eg wastes
The processes involved include diffusion, osmosis and active transport

3. Structure of the cell membrane
Fluid mosaic model
Describe the roles of:
Phospholipids
Waterproof barrier, acts as a bubble, main constituent
Proteins
Act as carriers, receptor sites, antigens, channels
Carbohydrates
Act as receptor sites, antigens

4. Exchange of material
Small particles eg water, ions can pass through the gaps between the phospholipids
Larger molecules pass through channels in the proteins or are carried by special proteins

5. Movement of particles - diffusion
Occurs without energy
Particles will move from higher concentrations to lower concentrations

6. Movement through membranes

7. Diffusion through membranes
Membranes are differentially permeable
Permeable substances (eg small particles) move through
Impermeable substances (eg large particles) can’t move through
Movement is from areas of high concentration to areas of low concentration
Energy is not needed

8. Facilitated diffusion
Allows larger or less permeable substances to cross
Involves channel proteins
Energy is not needed

9. Osmosis Movement of water
This occurs from areas of high water concentration (low concentration of solute) to areas of low water concentration (high concentration of solute)

10. Concentration gradient
This refers to the difference in concentration across membranes
The steeper the gradient,
the greater the movement
Osmotic pressure refers to the pull of water due to concentration gradients

11. Active transport Movement against a concentration gradient.
Energy is needed

12. Ion pumps Involves special proteins that act as pumps
Allows cells to maintain ion concentrations that are very different from the external environment
Energy is used

13. Endocytosis
Movement due to folding of membrane and bringing in the trapped substances
Energy is needed
Phagocytosis – solid substances trapped
Pinocytosis – liquids are trapped

14. Exocytosis
Movement due to vacuoles moving to membrane and attaching to release contents
Energy is needed