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Surface Tension of Cells
Name: John B.
Status: Educator
Age: 40s
Location: N/A
Country: N/A
Date: February 2004
Question:
I have been reading that water has a dyne or surface tension and that cells do
not take on water if the dyne of the water is too high. Is that true and if so how can a
person lower the surface tension or water dyne so that our cells will hydrate better and
expel cellular waste. In other words, how can the dyne of water be lowered so that the
cell will take in more water?
Replies:
You have a mixup of terms here. Surface tension is the ratio of the energy required to increase
a surface area an incremental amount, i.e. (INCREASE IN ENERGY)/(INCREASE INAREA) = S.T. The
units of the surface tension, (S.T.) are (ergs/cm^2) or the equivalent units (dyne*cm). The
units of (dyne*cm) are expressed as a [FORCE(dyne)*DISTANCE(cm)]. My preference is to think
of surface tension in terms of the increase in energy per increase in area, but that is a
personal choice. The numerical value of the S.T. is identical in both cases. So where you
have used the word "dyne" in your inquiry substitute the word "surface tension".
At 25 C. the S.T. of water is about 72 erg/cm^2 which, for most liquids except metals,
is large. The surface tension is caused by hydrogen bonds formed along the surface of the
water. Much like the stretching of a balloon. If a surface active agent (SURF-ACT-ANT) is
added to the water and if it has a higher concentration at the surface than in the bulk
liquid the surface tension will decrease a lot, even at very low concentrations of
surfactant. Surfactant molecules usually have a water loving end (hydrophylic) and a
water hating end (hydrophobic), because this dual functionality tends to make them
accumulate a small excess concentration at the surface of the water. Common soap is
an example. Surfactants generally will cut the surface tension in half to one third the
value of 72 ergs/cm^2 for water.
While surface tension plays a part in the exchange processes in cells, the osmotic pressure
plays an equal and often larger part. What "drives" the osmotic pressure is a difference in
electrolyte concentration across a cell boundary. Water will tend to move from regions of
low electrolyte concentration to regions of high electrolyte concentration, and this force
(i.e. pressure = force/area) can be very large.
Vince Calder
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Update: June 2012
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