Diffusion

Fill in the blanks on your sheet as we go through the ppt

DiffusionDiffusion is the movement of molecules from an

area of high concentration to an area of low

concentration, until evenly spread out.

Why is diffusion important?All living cells rely on diffusion to live.

They use it for:

getting raw materials for respiration (dissolved

substances and gases) removing waste products (eg. from respiration)

photosynthesis in plants (raw materials in, waste products out)

Examples…

Respiration- gas exchange

SEM photos of lung alveoli

In breathing you exchange carbon dioxide (CO2) and oxygen (O2) between

alveoli in the lungs and the blood.

This is an example of diffusion.

Respiration- in cellsfood + oxygen carbon dioxide + water + energy

Respiration & diffusion

Photosynthesis & Diffusion

Carbon dioxide

diffuses in through

the stomata

Oxygen and water diffuse

out of the stomata

carbon dioxide + water oxygen + glucose

OsmosisOsmosis is a special case of diffusion.It is the net movement of water across a selectively permeable membrane from a high concentration to a low concentration.

The cell membrane has very small holes in it. Small molecules can pass through, but larger ones cant.

We say it is selectively permeable.

Selectively permeable membrane ???

High Water Concentration,

few molecules of solute.

Dilute solution

Low Water Concentration, many

molecules of solute.

Concentrated solution

Water molecule Solute moleculeKey:

Water concentration gradient

Water movement

In osmosis water moves both ways to balance up the concentrations. The overall (net) movement is to the area of low water concentration.

Osmosis in action

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

Have a look at this video and answer the questions on the next slide:

1 Osmosis is best defined as the movement of

A) molecules from an area of high concentration to an area of lower concentration.

B) molecules from an area of low concentration to an area of higher concentration.

C) water molecules across a membrane from an area of low water to an area of higher concentration.

D) water molecules across a membrane from an area of high water concentration to an area of lower concentration.

E) water molecules inside a container.

2Which of the following will pass through a cell membrane most easily?

A) small polar molecules B) small nonpolar molecules C) large polar molecules D) large nonpolar molecules E) large neutral molecules

3 A red blood cell placed in a hypertonic medium will

A) expand. B) burst. C) shrink. D) have no change in shape. E) become a white blood cell.

4 A 5% urea solution is hypotonic to a 10% urea solution.

A) True B) False

5 If a cell is placed in an isotonic medium, there will be no net movement of water.

A) True B) False

Now let´s go outside and act it out!1. Nominate some sugar molecules

2. Everyone else is a water molecule

3. Draw a dashed line down the middle of the playground with chalk (your selectively permeable membrane!)

4. Arrange your water molecules either side of the membrane

5. Add your sugar molecules to one side and see if equilibrium can be restored by water moving in the right direction!

6. What happens if you remove some of the water molecules?