Diffusion and Osmosis

Cells have to control what leaves and what enters the cytoplasm.

Water and solutes move according to their concentration gradient

Everything naturally moves away from where it is concentrated and towards where it is less concentrated

This natural movement is called diffusion.

Concentration gradients form when there is a difference in concentration between two placesDiffusion takes place until the

concentration reaches equilibrium

Oxygen naturally diffuses into animal cells because they use up oxygen as they turn food into energy

Carbon dioxide builds up as cells use the oxygen

The concentration of oxygen outside is higher, so the net movement of O2 is inward.

The concentration of CO2 is higher inside the cell and has a net movement outside the cell.

The cell membrane does not stop the diffusion of CO2, O2, or water molecules

CO2, O2, and H2O are smallmolecules they each move down their

individual concentration gradients until equilibrium is reached.

This makes the cell membrane semipermeable.The movement of water through

a semipermeable membrane that blocks solutes from movingis called osmosis.

Osmosis is the diffusion of water through a semipermeablemembrane

Osmosis is used by plants to lift water upward. All the plants cells must do is maintain a highersolute concentration inside their cells.

Osmosis can pull water into of a cell if the cell is placed in an environment with a lowersolute concentration

Hypotonic means lower solute concentrationanimal cells can rupture in

hypotonic environmentsplant cells are protected from

rupture by their strong cell walls

Osmosis can also pull water out of a cell if the cell is placed in an environment with a highersolute concentration

Hypertonic means higher concentration of solutes A cell placed in a hypertonic environment

will lose water and shrink.

Plant cells plasmolyze when placed in very salty water.

Isotonic means balanced Cells in an isotonic environment experience

no net flow of water due to osmosis.

The water flowing in is balanced by the water flowing out

Hypertonic = higher = dehydrating environment, cells shrink

Hypotonic = lower = bloating environment, cells swell

Isotonic = equal =homeostatic environment, cells “happy”

Solution Examples

Quick Osmosis Movie

Iodine Ziplock Experiment

Lettuce Experiment

Egg Experiment