Osmosis is constantly happening in our cells, but we are unable to see how it works because our cells are so tiny. In this fun and easy experiment, you will be able to discover the magic of osmosis in a cell that you can see – an egg!
What is Osmosis?
What is osmosis? How does it work
Osmosis is a process within our cells that allows water to pass through a semi-permeable membrane.
Osmosis will move water down its concentration gradient from areas of high water concentration to areas of low water concentration.
What is a Semi-Permeable Membrane?
When a cell membrane is permeable to a molecule, it will allow it to pass through and enter or leave the cell.
A semi-permeable membrane is a cell membrane that will only let some molecules move in and out of the cell (e.g. water).
However, some bigger molecules like salt are unable to pass through the cell membrane because it is not permeable to it.
Materials
- 2 Raw eggs
- 1 Large glass container
- 2 Medium glass containers
- Vinegar
- Salt
- Tap water
- Paper or notebook to write down observations
- Writing utensil
- Permanent marker
- Measuring Scale (or Ruler)
- Food Coloring (Optional)
How to Do the Osmosis Experiment with an Egg
Step 1
Fill the large glass container with vinegar and carefully place both eggs in it.
Make a prediction! What do you think the eggs will look like after 15-30 minutes of sitting in vinegar?
Step 2
Check back in 15-30 minutes and write down what you see. Just like a scientist in a lab, you should be writing down observations every time you check on your egg!
STEM Q for You: Was your prediction correct? What do the eggs look like after sitting in vinegar for 15-30 minutes? …There should be bubbles forming and your eggs may appear to be moving. The formation of bubbles are an indicator that a chemical reaction is taking place. The shells are made of calcium carbonate, which contains oxygen. As the reaction occurs, oxygen is released and sticks to the shell. This makes the egg rise up, but when it reaches the top it is exposed to air so the bubbles pop, making the egg come down.
Step 3
Let your eggs soak in the vinegar for about two days or until you can no longer see the white shells of the eggs.
Make a prediction! What do you think the eggs will look like after 2 days of sitting in vinegar?
STEM Q for You: Why are you soaking your eggs in vinegar? What does the vinegar do? … Remember, osmosis only works with a semi-permeable membrane. So, we use the vinegar to remove the hard exterior shell of the egg to get to its semi-permeable cell membrane. The acidic vinegar will react with the calcium carbonate that makes up the shell and break it down into carbon dioxide, calcium, and water. As the vinegar breaks down the calcium carbonate, the egg’s shell will disappear!
Step 4
After about two days, the shells of your eggs should be gone. If so, take your eggs out of the vinegar and gently dry it. At this point, your eggs should be looking like water balloons! Take a minute to inspect your eggs and write down observations.
STEM Q for You: Why do the eggs look like water balloons? Why have the eggs changed size?
The eggs look like water balloons because the shell has been completely dissolved, and now we are able to see the cell membrane of the egg. The eggs changed size because vinegar has a higher water concentration than the inside of the egg. Due to the process of osmosis, water moved from the vinegar to inside the egg, causing it to expand.
STEM Q for You: Why did the egg stop expanding after a point? …Osmosis moves water until an equilibrium is reached, so until the concentration of water inside the cell is about the same as the concentration of water outside the cell.
Part B: Tap Water vs. Salt Water
Step 1
Label one egg A, and label the other B.
Weigh both your eggs and jot down their masses.
If you don’t have a measuring scale, you can just use a ruler to measure the length and width of each egg.
Step 2
Fill one medium glass container with normal tap water and place egg A in it.
Fill the second medium glass container with salt water and place egg B in it.
Make sure you label your containers as well.
Add different food colouring to each container for more fun!
Step 3
Make a prediction: How do you think each egg will change after they soak in their different solutions for a day?
Let the eggs soak in their solution for about a day.
Note down observations of what you see and what you think is happening.
Step 4
After about a day, take your eggs out of the solutions and gently dry them.
Weigh (or measure) them again and write down their masses.
Note down your final observations.
Step 5
Time to examine your eggs.
Poke them, pop them, and watch the yolk as you move them around.
The STEM Behind the Fun
How did egg A (soaked in tap water) change in size and weight? Why? …Egg A should be larger in size and heavier in weight because the egg has a higher salt concentration and lower water concentration than the surrounding tap water. Hence, osmosis will cause the water from the tap water to go inside the egg to increase its water concentration until equilibrium is met. The inward movement of water will cause the egg to expand.
How did egg B (soaked in saltwater) change in size and weight? Why? …Egg B should be smaller in size and lighter in weight because the egg has a lower salt concentration and higher water concentration than the surrounding saltwater. Hence, osmosis will cause water to be drawn out of the egg to increase the water concentration of the salty solution until equilibrium is met. The outward movement of water will cause the egg to shrink.
Why is Osmosis an Important Cellular Function?
Osmosis restores balance!
It is essential to the survival of our cells because it regulates our water and ion concentrations to ensure that our cells are maintaining constant internal conditions.
Too little water will make our cells shrivel up and too much water could make our cells burst.
Think about how the eggs are similar to your cells. How might your cells change to look like our eggs when you drink or eat certain foods?
Can you think of any other cellular processes?
Some examples are: Diffusion, homeostasis, photosynthesis, cellular respiration, etc.
