• Solution - a homogeneous mixture of 2 substances

• Solute - the dissolved substance• Solvent - the dissolving agent

Diffusion

• Random movement of molecules from an area of their higher concentration to an area of their lower concentration.

• Lighter molecules diffuse faster than heavier molecules

Diffusion occurs in both liquids and gases.Examples: sugar in water; perfume in air.

Osmosis

• Diffusion of water molecules through a semi-permeable membrane from an area of higher water concentration to an area of lower water concentration

• (An area of high water concentration has a low solute concentration, and visa versa)

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Figure 3.7 Generation of osmotic pressure by osmosis.

Solute concentrations of outside solutions relative to the inside of a cell:• Isotonic: the same solute concentration• Hypertonic: higher solute concentration• Hypotonic: Lower solute concentration

The plasma membrane is a semi-permeable membrane.The cytoplasm is completely enclosed.

Osmosis and Cells

Osmosis and cells

• In hypertonic environment, the cell shrinks. In a plant cell, this is called plasmolysis: the cell shrinks inside the cell wall.

• In hypotonic environment, the cell swells. An animal cell will burst, which is called lysis.

Differences between dialysis tubing and the cell membrane (both are selectively permeable):1. Dialysis tubing has pores. Whether or not a

molecule can cross depends only on its size.2. The cell membrane is made of a lipid bilayer.

Whether or not a molecules can cross depends on its chemical properties.

3. Proteins are embedded in the membrane, and regulate the passage of most molecules across the membrane.

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Membrane Lipids: basic structure

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The plasma membrane. (DON’T NEED TO KNOW THE DETAILS)