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.
Imagine pure distilled water. Now imagine dissolving salts in it. You could put a tiny bit, a larger pinch or an entire bowl of salt and dissolve in the water.
Now, due to complex chemical and physical reactions, if you separate two chambers of water by a semi-permeable membrane, and the chambers have water of different salt concentration, water naturally goes from low tonicity to high tonicity until they equal in concentration.
Ancient microbes exploit this, and this is literally how life on earth functions. Cell membranes are semi permeable and allow nutrient exchange using osmosis (I’m ELI5ing here).
The chamber with higher concentration is called hypertonic and the one with lower concentration is hypotonic. They both eventually become isotonic (equal concentration) if left undisturbed.
I made one crucial simplification by calling the above tonic instead of osmolar, but in ELI5 context, it should be hopefully okay.
Finally, we also use the reverse of the osmosis process to purify water from sea water. Basically, we can use electricity to force the reverse flow of water from high sanity to low salinity to end up with pure water. RO treatment plants use this principle.
https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/osmosis
Osmosis is water moving across a semi-permeable membrane. You can picture it as water wanting to even things out. Matter doesn’t “like” to be scrunched up, it wants to spread out if it has enough energy.
If you have a wall that only lets water through, water will want to go dilute the dissolved solids like salt or sugar. In biology the iso is in reference to a typical cell. If you stick a cell in a super salty solution, the water in the cell will leave. If you stick a cell in pure water, the water will go in. A classic demonstration is egg in vinegar: https://onelittleproject.com/egg-in-vinegar-experiment/
Water is unique. It will move to regions where there’s less water so because there’s less water there.
Let’s say you put a red blood cell into distilled water. Distilled water is pure water, like 100% water. The rbc, while having a large content of water, will have a lower water content, and thus distill water will enter the rbc and eventually cause it to burst
If by chance put a rack load of salt into the distilled water, it is no longer just pure water (as it’s now salt water). If it just happens that you but so much salt into the water, that now if you put a rbc into the salt water, the water content of the rbc would be greater in the rbc rather than the salt water. As said before, water will move to regions where there’s less water, so water would leave the rbc and enter the salt wayer, causing the rbc to shrivel
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