Transcript MEMBRANES
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 LAB? DID WE SEE DIFFUSION IN – 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“ 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 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!