1. Movement of Materials Across Membranes

2. Background Information
Most cells exist in liquid, making it easy for materials to move into and out of the cell.
Every cell membrane is selectively permeable, meaning that some substances but not others can cross them.
Particles have a tendency to move from a region where they are more numerous to a region where they are less numerous.

3. A Concentration Gradient is…
…a difference in the number of particles of a substance in two neighboring regions.
Particles tend to move down their concentration gradients (higher to lower concentration).

4. Particles of a substance tend to go from areas of higher concentration to areas of lower concentration.
True
False
It's not simply a case of movement in one direction. Particles move in both directions, but because one side has more particles to start with, they are more likely to move in one direction than the other. When both sides have the same number of particles, they are just as likely to move one way as the other way, so there will be no change in amounts - both sides will stay equal.

5. Diffusion is…
…the process by which particles of a substance move from areas of higher concentration to areas of lower concentration.
…the driving force behind the movement of materials across the plasma membrane.

7. A barrier separates two different substances.
The barrier is removed, and the substances move down their concentration gradients.
Equilibrium is reached.

10. Osmosis is…
…the diffusion of water molecules through a selectively permeable membrane from an area of greater concentration of water to an area of lesser concentration of water.

12. Based on the concept of osmosis, what would you expect to happen in this setup?
No movement of water will occur.
Water will move in both directions equally.
The net movement of water will be from side B to side A.
The net movement of water will be from side A to side B.

13. Osmosis Terminology When comparing two solutions…
…solutions with higher concentrations of solute are hypertonic
(hyper means "above").
…solutions with lower concentrations of solute are hypotonic
(hypo means “below”).
…solutions in which the concentrations are equal are isotonic
(isos means “equal”).

15. Which of the following correctly labels this setup?
left: isotonic / right: isotonic
left: isotonic / right: hypertonic
left: hypertonic / right: hypotonic
left: hypotonic / right: hypertonic

16. Imagine that the membrane shown below is impermeable to the solute molecules but permeable to water. Which way will water flow?
left to right
right to left

17. Normally, in the process of osmosis, the net flow of water molecules into or out of the cell depends upon differences in the
rate of movement of molecules inside the cell
concentration of water molecules inside and outside the cell
rate of molecular motion on either side of the cell membrane
concentration of enzymes on either side of the cell membrane

18. Facilitated Diffusion
Diffusion of a substance through a transport protein embedded in a membrane.
In facilitated diffusion, solute particles pass through a channel in a transport protein.

19. Facilitated Diffusion
Transport
Protein
Higher Concentration of Molecules
Outside Cell
Lower Concentration of Molecules
Inside Cell

20. Passive Transport
Diffusion, osmosis, and facilitated diffusion are all forms of passive transport across the plasma membrane because energy is not required for them to happen.
Like riding a bike down a hill, no energy is needed.

21. Active Transport
…involves a substance being forced through a transport protein in the plasma membrane against the concentration gradient (from lower to higher concentration).
Like riding a bike up a hill, an energy boost is required.

22. Active Transport Transport Protein Lower Concentration of Molecules
Outside Cell
Molecule to be carried
ENERGY
Higher Concentration of Molecules
Inside Cell

23. Molecule is transported to the other side of the membrane
Active Transport
Outside Cell
Molecule is transported to the other side of the membrane
Inside Cell

24. Which of the following types of transport across membranes was compared to riding a bike up a hill?
diffusion
osmosis
active transport
facilitated diffusion
Like an enzyme, a transport protein recognizes a specific solute, molecule or ion. During active transport, the protein uses energy, usually moving the solute in a direction from lesser concentration to greater concentration.

25. Diffusion Demo
Three agar blocks of various dimensions will be submerged in vinegar. The blocks have a color indicator that turns from pink to clear when the pH is acidic.
Question of the Day:
Predict which block will lose its color first. Explain the reasoning behind your prediction.

26. Endocytosis and Exocytosis
…the processes of taking material into (endocytosis) or out of (exocytosis) the cell by means of pockets of the cell membrane.

27. What process is shown here?
osmosis
exocytosis
endocytosis
facilitated diffusion

28. Osmosis Demo
Procedure: The water surrounding an Elodea leaf will be replaced with salt water.
Before the demo, write a paragraph describing what you expect to observe.
After you have observed osmosis, write a paragraph describing what you observed and what caused it to happen.
Correctly use the words equilibrium, hypertonic, hypotonic, and isotonic in your descriptions.