1. Transport Across a Membrane

2. Passive Transport
Diffusion is the movement of particles from an area of high concentration to an area of low concentration.
Ex- Food dye in a beaker of water, perfuming being sprayed in a corner and spreading throughout the entire room

3. Solutions Solutions are a mixture and contain both :
Solute- Ex- food dye, sugar, Kool-Aid
Solvent- Ex- water is the universal solvent
Within a solution, solute and solvent will move randomly until they are evenly distributed.
This state is called Dynamic Equilibrium. Water molecules are constantly moving but there is no net movement.

4. Rate of diffusion The rate of diffusion can be affected by:
Temperature
Movement of other organisms or particles in the solution
Pressure
Electrical currents
Molecule size

5. Osmosis Osmosis is the diffusion of water.
Water diffuses based on osmotic pressure.
The greater the osmotic pressure, the more likely it is that water will diffuse in that direction.

6. Isotonic Solution
The solute concentration and water concentration inside and out of the cell are equal.
No net gain or loss of water occurs.

7. Hypotonic Solution
The solute concentration in the solution is lower than the solute concentration inside the cell.
Water enters the cell.

8. Hypertonic Solution
The solute concentration is higher in the solution than the solute concentration in the cell.
Water exits the cell.

9. Facilitated Transport
Facilitated Transport is a form of passive transport.
Molecules move from a high concentration to a low concentration using carrier proteins or protein channels.

10. Can you…
Explain why both osmosis and diffusion move substances across a membrane.
Compare the energy requirements of passive and active transport.
Contrast the bulk transport of large and small substances into a cell.

11. Active Transport
Active transport moves molecules against the concentration gradient.
Molecules move from an area of low concentration to an area of high concentration.
Active transport requires energy in the form of ATP.

13. Bulk Transport Endocytosis Exocytosis
Cells take in substances by forming vesicles around the membrane. The plasma membrane invaginates around the substance and pinches off.
Phagocytosis- “cell eating”- engulfing large or solid particles
Pinocytosis- “cell drinking” engulfing liquid or small particles
Exocytosis
Intracellular vesicle fuses with the plasma membrane and secretion occurs

14. Receptor Mediated Endocytosis
Receptor protein must recognize a compatible molecule for it to be taken into the cell.
It is a selective process.
LDL receptors must function for cholesterol to be taken into the cell
Vitamins and peptide hormones also bind to specific receptors.

15. Can you… Compare facilitated transport with active transport.
Explain why active transport requires energy.
Summarize why a cell would use bulk transport rather than active transport.