FROM SLUGS TO CELLS…

It’s all about balance!  Cells are constantly “trying” to maintain a balance –(a.k.a. HOMEOSTASIS)  Accomplished by 3 factors: –Diffusion –Osmosis –Cell Membrane function

DIFFUSION  Movement of any molecule into or out of the cell  Molecules move FROM areas of HIGH concentration TO areas of LOW concentration

DIFFUSION  WHEN DID WE SEE DIFFUSION IN LAB? –All lab stations involved SOMETHING moving across the cell’s membrane! –When water moved…that was a special type of diffusion…

OSMOSIS  Movement of water across a cell membrane  Water moves from where there is MORE water to where there is LESS water  How could we tell when water moved across the membrane? –"BLOB OSMOSIS“ "BLOB OSMOSIS“"BLOB OSMOSIS“  Why does the cell blow up? Why does it shrink?

HYPOTONIC SOLUTIONS  The word "HYPO" means less, in this case there are LESS SOLUTE (salt) and MORE WATER on the OUTSIDE  Water will move into the cell.  In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting  In animal cells, the cell may be in danger of bursting

HYPERTONIC SOLUTION  The word "HYPER" means more,  MORE SOLUTE (salt), LESS WATER molecules OUTSIDE the cell  WATER MOVES OUT OF THE CELL  In plant cells, the central vacuole loses water and the cells shrink, causing wilting  In animal cells, the cells also shrink.  In both cases, the cell may die.  This is why it is dangerous to drink sea water - its a myth that drinking sea water will cause you to go insane, but people marooned at sea will speed up dehydration (and death) by drinking sea water.  This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages.

SO…ARE CELLS ALWAYS SHRINKING AND SWELLING?  Not always…it’s about BALANCE!

ISOTONIC SOLUTIONS  Concentration of solute (salt) and water is EQUAL on both sides  Water will move back in forth EQUALLY but it won't have any result on the overall amount of water on either side.  "ISO" means the same, SO cell stays about the same size  Means the system is balanced…HOMEOSTASIS ACHIEVED!

WHAT’S A MEMBRANE GOT TO DO WITH IT???  Membranes Are Picky! –Not all substances diffuse across a cell membrane  Depends on the molecule’s: –Size –Charge –Shape –So…We say the membrane is SELECTIVELY PERMEABLE…like a bouncer at a club…

MEMBRANES (cont.)  Cell membranes have “parts”, too!  Glucose Glucose

SLUGS REVISITED  TYPE II:  Use the terms hypertonic, osmosis, and solute to explain why this scenario would be a “Slug Vacation Disaster.” UNDERLINE EACH TERM AS YOU USE IT!