Diffusion

Diffusion Def: the movement of molecules from an area

of high concentration to an area of low concentration.

No cellular energy is involved (this is called PASSIVE)

What does passive mean?

Concentration GradientDef: A gradual change in the amount of a

specific chemical or molecule from one place to another.

Example: You would notice a concentration gradient as you walked away from the source of an odor – the smell would GRADUALLY become weaker.

A concentration gradient on a graph looks like a hill. The top of the hill is closest to the source.

Think: molecules flow from the top of the hill down…

(source) Highest concentration of molecules – close to source

Lowest concentration of molecules – farthest from source

Distance from source

Kinetic Energy of Particles causes diffusion.

Molecules are always moving due to heat energy unless they are at absolute zero

This allows the molecules to move away from the source and down the concentration gradient.

Brownian MotionBrownian Motion is a result of kinetic energy inside all particles and the name for the random motion of the particles that allows diffusion.

Very tiny particles in a liquid, when highly magnified, appear to dance aroundVibrating at randomCaused by the impact of molecules (so small you can’t see them) bumping randomly on all sides.

Brownian MotionThe first recorded observation was made in

1785 by Jan Ingenhauz using charcoal dust. [Ref: Nature, 7 June 2001 p 641]  Brown observed the movement in living particles, decided to try several other nonliving

substances to be sure there was no 'life force‘

“discovered” that the motion is a property of all microscopic matter.

Because of his 'systematic investigation' Brown wins the accolade of having the jittering motion named after him.

How Diffusion Works - AnimationWrite several bullet points about what

happens in the animation.

You should accompany those notes with pictures.

Watch and listen to it one time through, then play it again and take notes.

Dynamic Equilibrium Molecules will continue to move in the

direction of lowest concentration until concentrations are equal.

Once concentrations are equal, molecules continue to move but they move equally in all directions.

This is called dynamic equilibrium.

Diffusion to Dynamic Equilibrium

In Dynamic EquilibriumMolecules will continue to move back and forth but in equal amounts

This happens in cells becauseCell membrane usually controls movement of materials into and out of cell.

But, pores in membrane allow small molecules (water, salts, & gases) to pass through.

Example: O2Ex: many cells need O2 which is carried by

the bloodstream and is small enough to fit through pores.

50% O2

50% O2

50% O2

50% O2

bloodstreambloodstream

bloodstream

bloodstream

bloodstream

bloodstream