1. Passive Transport

2. Concentration- the amount of a solute dissolved in a given solvent
-Without movement across the cell membrane, wastes would build up inside and needed materials would not enter. This movement is driven by concentration differences in and out of the cell.
Concentration- the amount of a solute dissolved in a given solvent

3. Concentration Gradient
-When a substance is more concentrated in one area than another, it forms a concentration gradient, a gradual difference in concentration of a substance as a function of distance.

4. Concentration Gradient
-Molecules and ions are in constant motion because they have energy. They will naturally move from a region of high concentration to a region of less concentration.
-This is called movement down a concentration gradient. It requires no energy input to occur as the particles already have energy.

5. Passive Transport
-allows substances to pass through the cell membrane without the cell using energy

6. 3 Examples of Passive Transport
1. Diffusion 2. Facilitated Diffusion 3. Osmosis

7. Diffusion -aka simple diffusion
-when a substance spreads evenly through a
liquid or a gas

8. Substances that move by diffusion
-Diffusion is the driving force behind the movement of many substances across the cell membrane, such as the passage of small nonpolar molecules like oxygen and carbon dioxide across the phospholipid bilayer, easily slipping between phospholipids in and out of the cell.

10. Unequal Concentration….
-If there are unequal concentrations on either side of a cell membrane,

11. Equal distribution
-and the substance can cross the cell membrane, it will move where it is less concentrated until evenly distributed.

12. Equal Concentration on both sides of the membrane
-At that point, the concentration of the substance on both sides of the cell membrane is the same, and equilibrium is reached.

13. Continuing movement of particles
-Even when equilibrium is reached, particles of a solution will continue to move across the membrane in both directions.
-This is not considered diffusion because diffusion requires a concentration gradient to occur.

14. Facilitated Diffusion
-Some molecules cannot directly diffuse across the membrane, such as large molecules, charged ions, and polar molecules.

15. Facilitated Diffusion
-aka special diffusion
-substances must diffuse across the membrane through special transport proteins
-each protein only allows a specific substance to pass through the cell membrane

16. 2 types of proteins involved in facilitated diffusion
Channel Protein- faster; tubelike openings
2. Carrier proteins- bind to molecules or ions and change shape

18. Osmosis: An Example of Facilitated Diffusion
-The inside of a cell’s lipid bilayer is hydrophobic—or “water-hating.” Because of this, water molecules have a tough time passing through the cell membrane.

19. Osmosis: An Example of Facilitated Diffusion
-Many cells contain channel proteins,
known as aquaporins, tubes with hydrophilic centers, that allow water to
pass right through them.
-The more aquaporins, the
faster water moves in or out.

20. Osmosis
-the diffusion of water through a selectively permeable membrane

21. Osmosis
-For organisms to survive, they must have a way to balance the intake and loss of water.
-The net movement of water out of or into a cell exerts a force known as osmotic pressure.

22. Volume changes
-Because the plasma membrane is impermeable to some solutes, osmosis can change the volume of fluid inside a cell.

23. Water in or out?
-Placing cells in solutions of different concentrations affects whether water will enter or exit the cell; there are 3 possible types of solutions a cell can be exposed to

24. 1. Isotonic Solutions
- there is an equal amount of water and solute inside the cell as outside the cell
- when cells are placed in isotonic solutions, water will enter and exit the cell at the same rate
-cell will remain the same size

26. Iso means “equal” or “same”
-Our cells are surrounded by fluids, such as blood, that have concentrations of dissolved materials roughly equal to those in our cells. Our cells and these solutions are isotonic in relation to each other.

27. 2.Hypotonic Solutions
-when cells are placed in hypotonic solutions, water will flow into the cell because there is more solute in the cell than outside the cell
-causes the cell to swell

29. Osmotic Pressure
-Plant cells come into contact with fresh water; they are surrounded by tough cell walls that prevent the cells from expanding, even under tremendous osmotic pressure.
A plant cell holds its shape in a hypotonic solution, while an animal red blood cell does not.

30. 3.Hypertonic Solutions
-when cells are exposed to hypertonic solutions, water will flow out of the cell because there is more solute outside of the cell than inside the cell
-causes the cell to shrink

32. Hypertonic solutions and cells
-In a hypertonic solution, when water rushes out of the cell, animal cells shrink and plant cell vacuoles collapse.

33. Osmotic Pressure
-In plants, the movement of water into the cell causes the central vacuole to swell, pushing cell contents out against the cell wall.
-Since most cells in large organisms do not come in contact with fresh water, they are not in danger of bursting.