Sunday, February 26, 2012

Chemistry Thursday (on Sunday): Osmosis

What the heck is osmosis? "Osmosis is the movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, aiming to equalize the solute concentrations on the two sides. It may also be used to describe a physical process in which any solvent moves, without input of energy, across a semipermeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations." It's a type of passive transport, which means it doesn't require energy to make it happen.

An easier way to look at it is to think of osmosis as a process of balancing out a concentration of something. There's more of something on one side of the barrier and less on the other side, so it's an attempt to balance it out so there's relatively equal amounts of each thing on each side. In the case of the red blood cells, you can see that it's trying to balance out how much water is on each side of its membrane. It takes a little in - oops, too much - then lets some out. It will do this until the water amount is just right!

This is one of the reasons we can't drink sea water! Sea water contains high levels of salt (sodium chloride or NaCl), so much salt that our bodies can't excrete the sodium quick enough to bring our bodies into balance. The concentration of sodium in our blood reaches toxic levels, "removing water from cells and interfering with nerve conduction". (From Wikipedia) We have a seizure, then die.

Water, water, everywhere, and all the boards did shrink.
Water, water, everywhere, nor any drop to drink.
- Rime of the Ancient Mariner.

Check out the song "Rime of the Ancient Mariner" from Iron Maiden's album, Powerslave. Awesome! Completely and utterly awesome! I couldn't resist an Iron Maiden reference in a chemistry post!

This is one of the arguments for why glycerin allegedly removes water from your skin when it's not so humid outside, which is why it's Chemistry Sunday - I'm researching this claim, and realized that osmosis is an important part of understanding how our skin works!

Here's a little video on the process of osmosis!

Join me tomorrow for more fun with chemistry as we take a look at electrolytes!


p said...

Hi Susan, I'm guessing you're already planning to get into this... but I've heard conflicting things about whether the skin absorbs water during a shower or bath. It seems to me that it should absorb a small amount through osmosis (the moisture in our skin has a greater concentration of solutes than water does). But I've heard people say that skin actually loses water in the shower, which doesn't make sense to me.

I've been under the impression that our skin absorbs some water in the shower, but it evaporates off quickly after a shower unless you apply an occlusive moisturizer immediately after the shower. I found this page on winter dry skin, by the University of Iowa hospitals, which recommends moisturizing within 3 minutes of getting out of the shower:

(Incidentally, the University of Iowa page says some pretty weird stuff about the 'alcohol' content of lotions makes them drying - it seems to me that they're confusing fatty alcohols with ethanol!)

Ben said...

I'm really digging this Iron Maiden song...

Anonymous said...

So simplified!


Jip said...

Thanks for the refresher course.