What is Osmosis?
Before we do an osmosis experiment, let’s first understand what osmosis is. Osmosis is the movement of water through a semi-permeable membrane see the . During osmosis, the water moves from an area of low-concentration (i.e. where there’s only a little bit of solute) to an area of high-concentration (i.e. where a lot of solute is present).
That means that there are 2 key points to remember about Osmosis:
- It’s the movement of water.
- It requires a semi-permeable membrane.
One way you can think about this concept is that the water is trying to dilute whatever is nearby, and that there is some sort of barrier (the semi-permeable membrane) between the water and the “stuff” being diluted. The water has to be able to move through the barrier, but not the particles being diluted.
Osmosis vs Diffusion
Osmosis can be easily confused with Diffusion, especially when you are beginning your nursing studies (or if it’s been a while since you’ve studied Anatomy & Physiology!).
Unlike Osmosis, which is the movement of water through a semi-permeable membrane, diffusion is the movement of particles (solute) and doesn’t necessarily involve a semi-permeable membrane
One of the main reasons that these two processes are frequently confused is because they are often happening simultaneously in the human body. Osmosis and Diffusion are both essential processes in the body that work together to help maintain homeostasis.
One of the reasons why it’s really difficult to understand complex processes occurring in the human body is because they are invisible to the naked eye. I can’t see my blood flowing through my veins and arteries, and I can’t see how the processes of osmosis and diffusion effect that blood flow. I certainly can’t see the electrolytes that are dissolved into my blood!
That is why I believe it’s sooo much easier for nursing students to understand these concepts when we can actually SEE a real life example in action! So here’s an osmosis experiment I developed that shows the effects of hypertonic, isotonic, and hypotonic fluids on eggs. (Spoiler alert: I broke an egg! ?♀️)
(Scroll past the video for more examples of osmosis, as as well as instructions on how to do this experiment for yourself!)
How to Do Your Own Osmosis Experiment at Home
So how can you do this Osmosis Experiment for yourself? Here’s the simple plan (with some explanations of what I would do differently next time!)
Make sure you have on-hand:
- 3-4 eggs of similar size (use 4 if you’re klutzy like me and might break one!)
- 3 containers (one for each egg)
- White vinegar (enough to cover all the eggs)
- 3 Testing Fluids:
- Isotonic (Saline solution, or make your own 0.9% saline solution by mixing salt and distilled water)
- Hypotonic (I used tap water, but if I did it again I would use distilled water instead)
- Hypertonic (I used high-fructose corn syrup)
- A towel…just in case you break an egg, too 😉
Step 1: Dissolving the egg shells
Side note: Dissolving egg shells in vinegar is way fun, and worth doing even if you don’t plan on trying the rest of the experiment. Squishy raw eggs are way cool. Just don’t try to bounce them. You’ve been warned ?
In order to get your semi-permeable membrane, you need to remove the egg shells without breaking the delicate membrane underneath. The best way I’ve found to do this is by soaking them in vinegar. Simply put all the eggs in a container together, cover them with vinegar, and wait.
For the osmosis experiment in the video, I left the eggs in the vinegar for several days after the shells had dissolved. After seeing the final results, I realized that vinegar acts as a hypotonic solution to the eggs, which means that the eggs probably absorbed quite a bit of water before I even started the “official” osmosis experiment.
Next time, I would check on my eggs more frequently, and pull them out of the vinegar solution as soon as the egg shell has dissolved.
Step 2: Applying the hypertonic, hypotonic, and isotonic solutions
Place each egg in its own, individual container. Label each container with the solution you will be adding. Then pour each solution into the container until the egg is completely covered:
- Isotonic (saline solution)
- Hypotonic (distilled water)
- Hypertonic (high-fructose corn syrup)
This part of the experiment is definitely not time sensitive. Once osmosis has caused as much water movement as is possible for this set-up, it will stop and wait patiently until you have time to check it 🙂
Step 3: Evaluate your results
Remove the eggs from their solutions and compare their sizes. Did you get the same results that I did? Did the egg from your hypertonic solution shrink? Did your egg in the hypotonic solution get fatter? Is your egg from the isotonic solution still look normal egg sized?
Now let’s apply these results to nursing school. Think about the different IV solutions we use in the body. What if that egg had been a red blood cell? What would happen to a patient who got too much hypertonic IV solution?
Osmosis is a real phenomenon that has real consequences for our nursing practice, so it’s important to make sure you understand what’s going on at the molecular level.
Osmosis doesn’t only happen in our bodies (or only in eggs, for that matter). It also happens all around us everyday! Here’s some examples of osmosis in action, both inside AND outside of the body
The kidneys filter our blood and make urine. It’s a pretty complex process that involves many moving parts, but two of the major processes are osmosis and diffusion. This is a perfect example of how they work together in the human body.
Salting a Slug
The cells of slimy slugs contain a relatively large amount of water. If you were to sprinkle salt onto a slug, that water would start exiting the cells in an attempt to “dilute” the salt. If enough salt is applied, then the slug will get extremely dehydrated and die. Eww.
Pruned and Wrinkly Fingers
Ever noticed how wrinkly your fingers and toes can get after you’ve been soaking in the pool or the bathtub for too long? That’s osmosis! The water in pools and tap water generally has a lower concentration of solute than our skin cells do. This causes the water around us to try and dilute the solute in our skin.
So the next time you notice your wrinkly skin after a bath, you’ll know it’s because your carrying some of the bath water in your skin cells!
You can easily do another osmosis experiment while you’re cooking! Some recipes call for dicing, salting, and resting your veggies before cooking. When you do this, you’ll find that the salt triggers the process of osmosis. Just like the example with the slug, water from inside your veggies will start exiting in an attempt to “dilute” the salt on the surface.
Not only is this a fun experiment, but it can concentrate the flavors of your vegetables and make the final dish less watery.
When you have too many sodium ions in your blood vessels, then the water in your body will work to bring you back to homeostasis. The water can move into your blood vessels from the interstitial space, or even from your red blood cells! A little bit of movement is totally normal, but as you can imagine, you don’t want a ton of water leaving your red blood cells or they will quickly end up looking like a salted slug!!
There are many, many more examples of osmosis all around us. Share your ideas in the comments below!
(Article updated 7/21/2018, Originally published 6/26/2012)