Osmotic Pressure

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drzakisadiq

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Can someone explain to me what causes an increase in osmotic pressure, or basically tell me exactly what osmotic pressure and how it builds up. I know the physiology of it and how it relates to capillaries, but I'm looking for the basic form of it. Thanks

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think of it this way...


area where there is "less" water due to ions or whatnot water will attempt to flow into the area of lesser conc, same as diffusion.

So if you have an imperimable membrane and have ions present on one side water will be at a lower conc at that side due to the presence of the ions, so water from the side with no ions will flux to the side with ions.

Actually water flows both ways but the observation is a net increase or flux to the side with more ions, thats the bases of osmotic pressure.


404bda0ea31fa916b2ae321a64d27177.png
,

where
i is the van 't Hoff factor M is the molarity R is the gas constant, where R = 0.08206 L · atm · mol-1 · K-1 T is the thermodynamic temperature (formerly called absolute temperature) van 't Hoff factor i is the number of moles of solute actually in solution per mole of solid solute added. Equivalently, i refers to the ratio of true molecular mass to calculated molecular methods by colligative methods
(thats from wiki)

be careful with the van't hoff factor something like 1 mole of NaCl will actually yeild TWO moles of ions (Na+ and Cl-)

so now if you have the typical exp with a tube bent upwards and water on each side with a membrane if you add salt to one side you will notice that the water level rises on that side, the difference between water levels on each side is the observed osmotic pressure due to water going from the hypotonic side (water with no ions) fluxing to the hypertonic side (water with ions) thus it attempts to balance the imbalance of water conc....
 
The contractile vacuole of euglena decreases its rate of contraction when the organism is transferred from fresh water to sea water. this is explained by:

a) a decrease in the osmotic pressure of the environment
b) an increase int he osmotic pressure of the environment
c) the nitrogenous wastes can remain in the cell because of a higher salt concentration outside the cell
d) excess salts are eliminated without the loss of water
e) salt inhibits the contractile apparatus

i keep picking A because in fresh water, water continually flows into the organism, so that makes me think high osmotic pressure.

so when its put into a hypertonic solution, water flows out of the organism, thus lowering the osmotic pressure on the organism, right?

can someone please explain the answer better, i may have the concept backwards :confused: thanks guys!
 
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