1. Membrane Transport

2. Solute Movement across Lipid Bilayers
Materials can move across the cell membrane in different ways.
Passive transport does not require an input of energy.
Active transport requires energy to move substances across the membrane.
Small molecules and ions in solution are called solutes, have thermal energy, and are in constant, random motion.

3. Diffusion along a Concentration Gradient
A difference in solute concentrations creates a concentration gradient.
Molecules and ions move randomly when a concentration gradient exists, but there is a net movement from high- concentration regions to low-concentration regions. Diffusion along a concentration gradient increases entropy and is thus spontaneous.
Equilibrium is established once the molecules or ions are randomly distributed throughout a solution.
Molecules are still moving randomly but there is no more net movement.

4. Diffusion
Solutes in motion move from a higher concentration to one that is lower.
The direct movement of molecules and ions (solutes) is called diffusion.
Diffusion is an example of passive transport.

6. Osmosis: Passive or Active?
Water moves quickly across lipid bilayers.
The movement of water is a special case of diffusion called osmosis.
Water moves from regions of low solute concentration to regions of high solute concentration.
This movement dilutes the higher concentration, thus equalizing the concentration on both sides of the bilayer.
Osmosis only occurs across a selectively permeable membrane.

8. Osmosis and Relative Solute Concentration
The concentration of a solution outside a cell may differ from the concentration inside the cell.
An outside solution with a higher concentration is said to be hypertonic to the inside of a cell.
A solution with a lower concentration is hypotonic to the cell.
If solute concentrations are equal on the outside and inside of a cell, solutions are isotonic to each other.

9. Osmosis in Hypertonic, Hypotonic, and Isotonic Solutions
In a hypertonic solution, water will move out of the cell by osmosis and the cell will shrink.
In a hypotonic solution, water will move into the cell by osmosis and the cell will swell.
In an isotonic solution, there will be no net water movement and the cell size will remain the same.

11. Let’s practice

12. Hyper-, Hypo-, or Isotonic? (in your notes)
Use arrows to show the direction of water movement into or out of each cell.

13. Label the Plant Cell
What type of solution are they in?

14. Label the Red Blood Cells Why should you worry about this?
What type of solution are they in?

15. Membrane Proteins Affect Ions and Molecules
The transmembrane proteins that transport molecules are called transport proteins. There are three broad classes of transport proteins, each of which affects membrane permeability:
Channels
Carrier proteins or transporters
Pumps

17. Facilitated Diffusion via Channel Proteins:(Passive transport)
Cells have many different types of channel proteins in their membranes, each featuring a structure that allows it to admit a particular type of ion or small molecule.
These channels are responsible for facilitated diffusion: the passive transport of substances that would not otherwise cross the membrane.
Glucose is a building block for important macromolecules and a major energy source, but lipid bilayers are only moderately permeable to glucose.
A glucose transporter named GLUT-1 increases membrane permeability to glucose.

18. Active Transport by Pumps
Cells can transport molecules or ions against an electrochemical gradient.
This process requires energy in the form of ATP and is called active transport.
Pumps are membrane proteins that provide active transport of molecules across the membrane.
For example, the sodium-potassium pump, Na+/K+-ATPase, uses ATP to transport Na+ and K+ against their concentration gradients.

19. http://highered. mcgraw-hill

20. Secondary Active Transport
In addition to moving materials against their concentration gradients, pumps set up electrochemical gradients.
These gradients make it possible for cells to engage in secondary active transport, or cotransport.
The gradient provides the potential energy required to power the movement of a different molecule against its particular gradient.

21. Endocytosis and Exocytosis (Active transport)

22. Summary of Membrane Transport
Give examples of types of transport across the membrane.
Diffusion and facilitated diffusion are forms of ________transport and thus move materials down their concentration gradient and ________require an input of energy.
______transport moves materials against their concentration gradient and _______energy provided by _____or an electrochemical gradient.

23. Summary-homework
Intraveneous solutions must be prepared so they are isotonic to red blood cells. A 0.9% salt solution is isotonic to red blood cells.
a. Explain what would happen if you placed a red blood cell in a solution of 99.3% water and 0.7% salt.
b. Explain what would happen if you placed a red blood cell into a solution of 90% water and 10% salt.

24. 2. What would happen to a cell if placed in the following solutions
2. What would happen to a cell if placed in the following solutions? Explain in detail and illustrate.
Hypotonic
Isotonic
Hypertonic

25. Water Potential Water potential of 0 is high
-more negative number, more potential to move water
- occasionally a positive number
- determined by the solute concentration and pressure

26. Just like water moves from high concentration to low concentration (down the concentration gradient) water will move from high water potential to low water potential.
Ex: distilled water (no ions) has a water potential of 0.

27. Increase solute decrease water potential
Increase pressure increases water potential
When osmosis occurs water will move to areas where water potential is lower.
Ex: hypertonic: low H2O potential
hypotonic: high H2O potential

28. Water potential calculation
Ψ = - i C R T
i = Ionization constant (1 for sucrose)
C = Molar concentration of solute (from lab)
R = Pressure constant ( liter bars/mole K)
T = Temperature K (273 + °C of solution)
**pressure potential usually 0, do not take into account **

29. Water potential (Ψ) = pressure potential (Ψp ) + solute potential (Ψs)