1. Diffusion, osmosis and dialysis

2. Solution
Making a saline water solution by dissolving salt (NaCl) in water. The salt is the solute and the water the solvent.

3. Concentration
These glasses containing red dye demonstrate qualitative changes in concentration. The solutions on the left are more dilute, compared to the more concentrated solutions on the right.

4. Diffusion The tendency of molecules to spread out
Molecules move from areas of their higher concentration to areas of lower concentration until equilibrium is achieved and the molecules and distributed equally.
The speed of diffusion is dependent on such factors as the temperature, the size of the molecule, and the type of medium.

5. Solute Diffusion Across the Plasma Membrane
Small, non-charged molecules can diffuse across a plasma membrane, but large molecules cannot diffuse across a membrane.
Glucose— Benedict’s reagent (small)
Starch— Iodine
(large)

6. Osmosis Special case of diffusion
Osmosis is the diffusion of water across the plasma membrane of a cell.
Water molecules follows its concentration gradient and moves from the area of higher concentration to the area of lower concentration. a.
less water (higher
percentage of solute)
more water (lower
10% 5%
<10%
>5%
solute
differentially
permeable
membrane
water b. c.
beaker
thistle
tube
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7. Tonicity
The relative concentration of solute (particles), and therefore also of solvent (water), outside the cell compare with inside the cell.
Isotonic Solution
Solute and water concentrations equal on both sides of plasma membrane
Hypotonic Solution
Concentration of solute lower than the cell
Hypertonic Solution
Concentration of solute higher than the cell

8. Osmotic effects on cells
In an hypertonic solution
Animal
cells
Plant
plasma
membrane
chloroplast
nucleus
cell
wall
Vacuoles fill with water
turgor pressure develops
chloroplasts - next to the cell wall
Vacuoles lose wate
the cytoplasm shrinks(plasmolysis)
chloroplasts- in the center of the cell
Water mainly enters the cell, which may
burst (lysis)
No net movement of water
Water mainly leaves the cell, which
shrivels (crenation)
central
vacuole
In an isotonic solution
In an hypotonic solution
No net movement of water
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9. Experiments and questions
1. Solute Diffusion across Plasma Membrane (page 48) which molecules can diffuse across the dialysis tubing, starch or glucose?
2. Osmosis (page 50) why the level of the syrup solution rises in the thistle tube?
3. Demonstration of Tonicity in Red Blood Cells (page 51)
4. Effect of Tonicity on Elodea Cells (page 52)