DIFFUSION & OSMOSIS

Diffusion: the gradual spreading out of molecules Molecules spread from areas of high concentration to areas of low concentration

Osmosis: a special TYPE of diffusion Osmosis is the diffusion of WATER through a membrane

3 Types of Solutions: Hypertonic Solution: Solution that has a lower concentration of water and a higher concentration of solutes than in the cell Water moves from high to low so… water will move out of the cell Cell shrinks called PLASMOLYSIS

3 Types of Solutions: 2. Hypotonic Solution: Solution that has a higher concentration of water and lower concentration of solutes than in the cell Water moves from high to low so… water will move into the cell Cell GROWS called CYTOLYSIS

3 Types of Solutions: 3. Isotonic Solution: Solution outside the cell has the same concentration of water as inside the cell Water moves into and out of the cell at the same rate No net gain or loss of water

WATER ALWAYS MOVES FROM HYPOTONIC TO HYPERTONIC

Cell membranes are….. Selectively Permeable (semi-permeable) -some things can get in/out, others can’t Analogy – like a screen on a window!

If you put a cell into a hypertonic solution, There’s more water inside the cell than there is outside the cell Water will move out of the cell 94% water, 6% solutes This will keep going on until the two solutions are balanced 95% water, 5% solutes If the cell loses water, it will Shrink (plasmolysis)

If you put a cell into a hypotonic solution There’s more water outside the cell than there is inside the cell 95% water, 5% solutes Water will move into the cell 94% water, 6% solutes This will keep going on until the two solutions are balanced Cell takes in water, it will grow = cytolysis

Osmosis video

CHECK YOUR UNDERSTANDING What happens to a cell in a HYPERTONIC solution? What happens to a cell in a HYPOTONIC solution? What happens to a cell in an ISOTONIC solution? Explain, using osmosis terms, why you should never drink sea water Explain, using osmosis terms, why leftover salad gets wilted if it already has salad dressing on it

Plant cells – don’t burst – protected by cell wall turgor pressure builds up

Single-celled pond creatures – don’t burst collect water into contractile vacuoles and spit it back out

How do cells get the stuff they need? If they can’t get it by diffusion, they may have to use energy to collect certain molecules ACTIVE TRANSPORT