Diffusion

Diffusion: molecules move from an area of high concentration to an area of low concentration.

Did you ever notice that that when a person farts, the person next to them notices first?

Diffusion doesn't just happen in liquids.

Molecules that cause odors diffuse through the air...whether the odor is your sibling's fart, or something delicious being cooked in the kitchen.

Diffusion is passive transport; it requires no energy.

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​Passive Transport

You will next watch two videos, answering questions about what you see and hear. The first video is the Amoeba Sisters' Diffusion. The second video shows you red blood cells under a microscope.

Molecules are always in motion.

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They continue to move after they have reached equilibrium.

Note: In this case, equilibrium is a balance of molecules on either side of the membrane.

Factors that affect the speed of diffusion

• Type of solvent

• Type of molecules

• Temperature (diffusion speeds up in heat)

• Distance

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​Small molecules that can diffuse through a cell membrane

​Water - H₂O

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Oxygen - O₂

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Carbon Dioxide - CO₂

​Small molecules that can diffuse through a cell membrane

​Solutions can be hypertonic, isotonic, or hypotonic to a cell.

Hypotonic solutions have a high concentration of water compared to the cell.

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In a hypotonic solution, cells can burst (explode).

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Hypotonic

Isotonic solutions have a concentration the same as the cell.

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In an isotonic solution, cells stay healthy.

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Isotonic

Hypertonic solutions have a high concentration of solute (salt, sugar) compared to the cell.

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In a hypotonic solution, cells can shrink.

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Hypertonic

Human blood: salt concentration of 0.9%

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Seawater: salt concentration of about 3.5%

Fun Fact