Diffusion and Osmosis

• Diffusion - the tendency of molecules to move from a higher concentration to a lower concentration until equilibrium is reached.

Higher concentration on the left

Equilizing outEqual on right & left

Fully diffused

Diffusion video

Passive Transport • Diffusion across a semi-permeable

membrane (ex: cell membrane).

• Cell does not use any energy for diffusion. It goes through the cell membrane without it opening up.

• Examples – water, alcohol, O2 and CO2,

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• Osmosis - The diffusion of water • Cell membrane doesn’t open up, just goes through.

Only works with very small particles.

Osmosis VideoQuickTime™ and a

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Hypertonic Solution

• Solution with a higher concentration of solute and a lower concentration of water.

• Makes the cell shrivel. Example: adding salt water

Video Link

Hypotonic Solution

• Solution with a lower solute concentration and a higher water concentration.

• More water moves in than out. Cell bloats. Example: Being in the bath too long causes wrinkled fingers.

Video link

Isotonic Solution

• Equal amount of water goes in and out of cell.

Video link

Effect on living cells

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Active Transport• Cell uses energy to move things in and out. Example:

food molecules• Cell membrane actually opens and closes.

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Active Transport Video

Exocytosis & Endocytosis

Endocytosis (substances “enter” the cell).

Ex: Food molecules

Exocytosis (molecules “exit” the cell.

Ex: Waste products