1. Osmosis & Diffusion
Packet #8
Sections 7.3 & 36.1

2. Diffusion

3. Introduction {Figure 7.11}
Atoms and molecules, above absolute zero, exhibit motion.
This random motion allows particles to move from an area of higher concentration to an area of lower concentration in an attempt to reach equilibrium.

4. Rate of Diffusion… Depends on four factors Temperature
Size of the molecule
Electrical charges
Concentration gradient

5. Categories of Diffusion I
Regular Diffusion
Movement of molecules down the concentration gradient
High to low
Facilitated Diffusion
Movement of molecules down the concentration gradient via a channel
In cells, these channels are found in proteins
More to come later
Active transport
Movement of molecules against the concentration gradient via channels and with the use of energy.

6. Osmosis
Special Case of Diffusion

7. Osmosis {Figure 7.12} Concise Definition
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Concise Definition
The diffusion of water (liquid solvent) across a selectively permeable membrane
Detailed Definition
Transfer of a liquid solvent through a semi permeable membrane, that does not allow dissolved solids (solutes) to pass from an area of high concentration to an area of low concentration

8. Osmotic Pressure, Osmotic Potential & Solute Potential

9. Osmotic Pressure Osmotic Pressure
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Osmotic Pressure
Is a measure of the tendency of water to move into a solution.
The driving force for the water and is the difference in water pressure on both sides of the membrane.
The differences in pressure provides a net pressure that is exerted by the flow of water as it moves through the semi-permeable membrane.
Class Illustration
Use students to illustrate the differences in pressure.
Five on side A and 2 on side B—most pressure going forward will be on side A giving a net pressure as the water moves from side A to side B.
If a solution is separated from pure water by a semi-permeable membrane, the pressure which must be applied to prevent osmosis is called the osmotic pressure

10. Osmotic Potential = Osmotic Pressure
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Osmotic Potential
Difference in osmotic pressure that draws water from an area of less osmotic pressure to an area of greater osmotic pressure.
The potential of a solution to pull in water
Value is always negative
The more concentrated the solution, the more negative its osmotic potential

11. Osmotic Potential = Osmotic Pressure = Solute Potential
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The presence of solutes, in the solutions, impact the direction of the movement of water.
The ability of a solution to pull in water depends on the number of solute particles present.
The higher the amount of solutes in the solution, the lower the solute potential.
The solution is more concentrated.
Remember, from previous slide, the value is always suppose to be negative.

12. Osmotic Potential = Osmotic Pressure = Solute Potential
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All three terms represent a measure of the ability of a solution to pull in water.
The value is always negative.
The more solutes present, the more negative the value.
Represented by s

13. Osmotic Potential = Osmotic Pressure = Solute Potential
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When two solutions have the same osmotic potential, they are said to be isotonic.
Where one solution has a greater osmotic potential compared to the other, it is described as being hypertonic.
i.e. It is more concentrated.
The solution with the lower osmotic potential is described as being hypotonic.
Less concentrated.

14. Pressure Potential {Figure 36.5}
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Solutions/Water are also under the influence of external pressures.
These external pressures are measure as pressure potential.
This force (pressure) is not the same as the one caused by the movement of the liquid solvent (water).
Represented by p
Negative or positive depending on conditions.

15. Water Potential Measure of the tendency of water to leave a solution.
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Measure of the tendency of water to leave a solution.
Combination of the sum of osmotic potential/solute potential and pressure potential.
 = s + p

16. Water Potential II
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When measuring the water potential of two solutions, the solution with the lower water potential receives water from the solution with higher water potential
Osmosis!

17. Friday, November 16, 2018
Cells and Osmosis

18. Pressure Potential in Plant Cells
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In plant cells, the cell contents press the plasma membrane against the cell wall—producing an external force called turgor pressure.
Results in a turgid plant cell
Pressure potential is positive
A plant cell can be considered as a solution of salts and sugars in the vacuole surrounded by a semi-permeable membrane

19. Pressure Potential in Plant Cells II
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Special plant cells that make up xylem, tissue that conducts water in plants, undergoes transpiration.
This transpiration results in a negative pressure potential.

20. Cells & Osmosis {Figure 36.6}
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21. Cells & Osmosis {Figure 7.14}
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