1. Key Ideas
What determines the direction in which passive transport occurs?
Why is osmosis important?
How do substances move against their concentration gradients?

2. 8-2 Cell Transport

3. Cell Transport
Must move substances of varying size, electrical charge, and composition into and out of the cell
2 types of transport
Passive
Does not use energy
Moves from a high concentration to a low concentration
Active
Requires energy
Moves from a low concentration to a high concentration

5. Passive Transport- Terms
Equilibrium
Results when the concentration of a substance is the same through out a space
Concentration
The amount of a particular substance in a given volume
Concentration gradient
Occurs when one area has a higher concentration than another area does.

6. Passive Transport-Simple Diffusion
The movement of particles from regions of higher density to regions of lower density across the cell membrane.
The direction of movement depends on the concentration gradient and does not require energy.

7. Passive Transport-Simple Diffusion

9. Diffusion Facilitated Diffusion

10. Passive Transport Facilitated Diffusion
Transport proteins
Helps ions and polar molecules diffuse through the membrane
2 types
Channel proteins or pores
Carrier proteins

11. Passive Transport Facilitated Diffusion
Channel proteins or pores
Act as a tunnel through the membrane
Allow specific ions, sugars, and polar molecules to pass
Carrier
Transports substances that fit within their binding site
Results in changing the shape of the protein and the delivery of the substance to the other side of the cell

12. Passive Transport Facilitated Diffusion

13. Passive Transport: Osmosis
the diffusion of water across a selectively permeable membrane
Allows cells to maintain balance as their environment changes.

14. Passive Transport: Osmosis

15. Passive Transport: Osmosis
Water Channels
form of facilitated diffusion
Polar water molecules must rely on channel proteins in the cell membrane that only allow water molecules to pass through.

16. Passive Transport: Osmosis
Predicting Water Movement
Hypertonic
Water moves out
Hypotonic
Water moves in
Isotonic
Water diffuses in and out of the cell at an equal rate

18. Effects of Osmosis
If left unchecked, the swelling caused by a hypotonic solution could cause a cell to burst.
Ways to prevent the cell from bursting
rigid cell walls of plants and fungi prevent the cells from expanding too much.
many plants are healthiest in a hypotonic environment.
Some unicellular eukaryotes have contractile vacuoles
which collect excess water inside the cell and force the water out of the cell.
Animal cells have neither cell walls nor contractile vacuoles.
avoid swelling caused by osmosis by actively removing solutes from the cytoplasm.

19. Active Transport Review Requires energy
Moves against the concentration gradient – move from low concentration to high concentration

21. Active Transport Pumps Requires carrier proteins
Ex. sodium-potassium pump
sodium ions bind to the carrier protein
through the use of energy(ATP) changes shape releasing sodium to the outside of the membrane
while open to the outside, potassium ions bind to the carrier protein
when the pump returns to its original shape the potassium ions are released on the inside.
For every 3 sodium ions taken out there are 2 potassium ions taken in

22. Active Transport Vesicles
Allows proteins, polysaccharides, and other substances that are too large to be transported by carrier proteins
Contain the same lipid bilayer as the membrane so vesicles can easily break off and fuse with the membrane
2 types
Exocytosis
Endocytosis

23. Endocytosis
the movement of a large substance into a cell by means of a vesicle
cell membrane folds inward creating a pouch for the substance to enter
once in the pouch it pinches off and forms a vesicle
these vesicles can fuse with lysosomes and other organelles

24. Active Transport

25. Exocytosis
The movement of material out of the cell by the means of a vesicle
Reverse process of Endocytosis
Vesicles fuse with the cell membrane and releases its contents to the outside of the cell
Used to export proteins modified by the golgi apparatus

26. Active Transport