1. Diffusion and Osmosis

2. Selectively Permeable
Some substances can pass through the membrane while other cannot
Why is this important?
Cells must let in needed materials (oxygen, food) while getting rid of waste products.
The cell membrane also acts as a selectively permeable membrane,controlling the materials that enter and leave the cell. Molecules like water, oxygen, and carbon dioxide are able to easily pass in and out of the cell through the cell membrane while other molecules like specific proteins are strictly kept in or out of the cell.
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3. Diffusion
Molecules move from an area of higher concentration to an area of lower concentration
What causes diffusion?
Random motion of molecules
Water
Dissolved molecules 2 3 1 4
Substances move into and out of a cell by one of three methods: diffusion, osmosis, or active transport.
Diffusion is the main process by which small molecules move across the cell membrane. Diffusion is defined as the process by which molecules move from a region of higher concentration to a region of lower concentration.
Concentration is the amount of substance in a given area.

4. Osmosis
Diffusion of water molecules through a selectively-permeable membrane
Dissolved molecules (i.e. glucose, starch) are called solutes
The liquid they are dissolved in is called the solvent
Osmosis refers to the specific diffusion of water through a selectively permeable membrane. Remember that molecules tend to move from an area of higher concentration to an area of lower concentration. In osmosis, water molecules move by diffusion from an area where they are highly concentrated to an area where they are less concentrated.

5. Effects of Osmosis on Cells
[water] = [solute]
Low [water] outside cell
High [water] outside cell

6. Transportation of Molecules
Passive Transport
Movement of dissolved molecules through a membrane WITHOUT using cellular energy
Active Transport
Movement of molecules through a membrane USING cellular energy
Passive transport includes the processes of diffusion and osmosis. In both forms of passive transport, molecules tend to move from a more crowded to a less crowded area in order to achieve a balance without using energy.
Active transport is the movement of molecules from a less crowded to a more crowded area with the use of energy. Molecules are "carried" into or out of the cell using some of the cell's energy.

7. Egg-speriment
Demonstrate the effects of osmosis using an egg to model a cell
Dissolve eggshells in vinegar (weak acid)
Submerge eggs in different aqueous environments
Measure volume of liquid remaining and egg circumference to determine movement of water
Vinegar
Sugar syrup
Distilled water
Colored water
Cola
Diet Cola
Salt water
Alcohol