1. Osmosis, Diffusion, Active Transport

2. Movements Through Cell Membranes
A. The cell membrane controls what passes through it.
B. Mechanisms of movement across the membrane may be passive, requiring no energy from the cell (diffusion, facilitated diffusion, osmosis, and filtration) or active mechanisms, requiring cellular energy (active transport, endocytosis, and exocytosis).

3. Diffusion, Osmosis and Concentration Gradient
Diffusion – the movement of a substance from a high concentration to a low concentration
Osmosis – the movement of WATER from a high concentration to a low concentration.
Concentration Gradient – the difference in concentration between a region of high concentration and a region of lower concentration

4. Passive or Active Transport:
Passive Transport - does not require cell energy
Examples: Diffusion, Facilitated diffusion and Osmosis  
Active Transport Requires cell energy (ATP)
Examples: Carrier mediated active transport, Endocytosis and Exocytosis

5. Methods of Transport:
1. Diffusion: the random movement of particles of a solute from an area of higher concentration to an area of lower concentration.
Particles always move with (down) a concentration gradient (the difference in concentrations across a membrane).
Passive transport.
Diffusion enables oxygen and carbon dioxide molecules to be exchanged between the air and the blood in the lungs, and between blood and tissue cells.

6. Equilibrium
Diffusion stops at equilibrium (when the concentrations across a membrane are equal).
The movement of molecules continues at equilibrium but the # of molecules moving across the membrane remains the same.
The rate of transport is dependent on:
1) if the material is solid, liquid or gas.
2) the size of the molecules.
3) temperature
Examples of molecules that can diffuse through the bilayer: carbon dioxide, oxygen, water but very, very slowly.

7. Diffusion through a Plasma Membrane

8. Osmosis
Osmosis: the diffusion of water through a selectively permeable membrane.
Passive transport
Water molecules move from a higher concentration OF WATER to a lower concentration OF WATER.
Water will move to where there is a greater amount of solute because there is less water there

9. Isotonic Solution
Isotonic solutions: the concentration of solute inside and outside of the cell is the same.
Isotonic:
Water in = Water out
No net movement of water.
Molecules in equilibrium.
Normal state for animal cells.
Cell in homeostasis.

10. Hypotonic Solution
Hypotonic solutions: the concentration of solute is lower outside the cell than inside the cell.
Have more water outside the cell so water moves into the cell
Causes an increase in pressure inside the cell: called turgor pressure (plants) or osmotic pressure (animals).
Increase in pressure in animal cells causes them to swell or even burst; gives plant cells shape and support.

11. Example Hypotonic Hypotonic: Water enters cell.
Cell swells and bursts (cytolysis).
Give plant cells shape and support.

12. Hypertonic Solution
Hypertonic solutions: the concentration of solute is higher outside the cell than inside the cell.
Have more water inside the cell so water moves out of the cell
Causes a drop in turgor or osmotic pressure: called plasmolysis.
Plasmolysis causes animal cells to shrivel up and plants to wilt.

13. Hypertonic Example Hypertonic: Water exits cell.
Cell shrinks (plasmolysis) due to    water loss.

14. The effects of osmotic pressure

15. Hypo, Iso, Hyper

16. The effects of osmotic pressure in a plant cell

17. Endocytosis and Exocytosis
- In endocytosis, molecules that are too large to be transported by other means are engulfed by an invagination of the cell membrane and carried into the cell surrounded by a vesicle. - Exocytosis is the reverse of endocytosis

18. Three forms of endocytosis
1. Pinocytosis is a form of endocytosis in which cells engulf liquids.
2. Phagocytosis is a form of endocytosis in which the cell takes in larger particles, such as a white blood cell engulfing a bacterium.
3.Receptor-mediated endocytosis allows the cell to take in very specific molecules (ligands) that pair up with specific receptors on the cell surface.

19. Receptor-mediated endocytosis