Passive TransportDiffusionOsmosis

BiologyUnit - Regulation

Diffusion

• Involves the movement of molecules from an area of high concentration to an area of low concentration

• Does not require energy (ATP)

Examples of Diffusion

Diffusion

• The movement of a substance down its concentration gradient

Equilibrium

• even at equilibrium the molecules move at random

Equilibrium

OsmosisIs all

about the

movement of

WATERmolecules

Learning Osmosis

• Water molecules diffuse from an area of low solute concentration to an area of high solute concentration

Learning Osmosis

• Water molecules diffuse from an area of high water concentration to an area of low water concentration

Isotonic

• When the concentration of solutes outside and inside the cell are equal.

Hypertonic

• When the concentration of solute molecules outside the cell is higher than the concentration in the cytosol

• The solution outside the cell is hypertonic to

the cytosol                                                                                                                                                                                                                                                                                                                                                       

  

Hyper = highHypertonic

Hypotonic

• When the concentration of solute molecules outside the cell is lower than the concentration in the cytosol

• The solution outside the cell is hypotonic to

the cytosol

Hypo = lowHypotonic

Effect of  Solutions on Cells

How do cells deal with Osmosis?

1) cells in hypotonic environment unicellular freshwater organisms (paramecium)

– water constantly diffuses in– They require low concentration of water in

cytosol– need to get rid of excess

water

How do cells deal with Osmosis?

– do this with contractile vacuoles• organelles that remove water• collect water and pump it out of cell

How do cells deal with Osmosis?

2) some cells cannot compensate for changes in solute concentration

– red blood cells lose their normal shape when placed in an environment that is not isotonic to their own

Normal Cells in Isotonic Solution

Cells in Hypertonic Solution

Cells in Hypotonic Solution

                                                                                         

                                   

                       Photomicrograph of blood cells in an isotonic solution.

                                   

                       Photomicrograph of blood cellsin a hypertonic solution; the puckered effect comes from theloss of fluid from inside the cell.

                                   

                       Photomicrograph of blood cells in a hypotonic solution; thebloated effect comes from the swelling of the cell.

Alright….

Let’s

test

your

new

knowledge….

What has happened to this cell?

Explain.