What are Osmosis and Hypo/Hyper/Isotonic Solutions? And how do they work?
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Osmosis is the process of water moving from one place to another through a semi-permeable barrier. You can think of the barrier like a screen that allows water to pass through but not other molecules.
Hyper/hypotonic refers to the relative concentrations of molecules in the water. It’s like saying hotter or colder, it has to relate to the other component you are comparing it to. Hypertonic means more non-water molecules, hypotonic means less non-water molecules, and isotonic means that they are the same.
So imagine if you have a container of water with a semi-permeable membrane separating it into two parts.
Then you add salt to one of those parts. The part without salt (or with less salt) will be hypotonic, the part with the salt will be hypertonic. Through the process of osmosis (and physics beyond the scope of EIL5), the water will move from the hypotonic part to the hypertonic part. So in the end the half of the container that has more salt in it will have more water in it since the water moves on its own to equalize the salt concentration. Osmosis actually generates force. In the above example, the water level will be higher on the side that has the salt in it since more water moved to that side. If you measure the salt concentrations on both sides and the difference in height of the water level between both sides, you can calculate the osmotic pressure.
This is a very important concept in medicine since most of our cell membranes act as semi-permeable barriers. For example, this is why we only administer saline or other isotonic solutions in IVs. If you administered a hypotonic solution, the salts in the blood would become more diluted, then water from the blood would osmos into the cells causing them to enlarge and pop. On the other hand, if you administered a hypertonic solution, water would osmos out of the cells causing them to shrivel up.
Usually this is a bad thing, but sometimes it is actually used as a treatment. For example if someone has swelling in the brain, you can administer a hypertonic solution of saline or certain sugars that will cause fluid to move out of cells. The cells will shrink and reduce the swelling in the brain.
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