BIOLOGY

Tiny molecules and large oil soluble substances

Can't pass through

• Most water soluble molecules
• ions
• Polar molecules

• lipid-soluble substances
• tiny molecules
• Small uncharged molecules
• Larger water soluble substances

Diffusion is the net movement of molecules from a region of high concentration to a region of lower concentration.

Passive

concentration gradient

The solute is being diffused in the solvent

• Osmosis is the passive net movement of water through a selectively permeable membrane, from an area of high concentration (an area where there are more free molecules) to an area of less concentration (less water molecules)
• The water is diffusion along it's own conentration gradient.

When a solute is added to water, the water molecules become attached. In a dilute solution though, there are more free water molecules than a concentrated one. When a semi permeable membrane separates a dilute and concentrated solution, the free water molecules will cross the membrane in both directions. However, since there are more free water molecules in the dilute solution, there will be a net movement of water molecules from the dilute solution to the concentrated.