Diffusion and Osmosis

Selectively Permeable Some substances can

pass through themembrane while othercannot

Why is this important?– Cells must let in

needed materials(oxygen, food) whilegetting rid of wasteproducts.

Diffusion Molecules move from an

area of higherconcentration to anarea of lowerconcentration

What causes diffusion?– Random motion of

molecules2

3

14

WaterDissolvedmolecules

Osmosis Diffusion of water

molecules through aselectively-permeablemembrane– Dissolved molecules

(i.e. glucose, starch)are called solutes

– The liquid they aredissolved in is calledthe solvent

Effects of Osmosis on Cells

[water] = [solute]

Low [water]outside cell

High [water]outside cell

Transportation of Molecules Passive Transport

– Movement of dissolvedmolecules through amembrane WITHOUTusing cellular energy

Active Transport– Movement of molecules

through a membraneUSING cellular energy

Egg-speriment

VinegarSugarsyrup

Distilledwater

Coloredwater Cola

DietCola

Saltwater Alcohol

Demonstrate the effects of osmosis using anegg 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