Thursday, May 28, 2020
Home DIY Stay-at-home science project: Enlarge gummy bears to reveal the secrets of osmosis

Stay-at-home science project: Enlarge gummy bears to reveal the secrets of osmosis

Pure water makes the bears swell up, but salt water keeps them pretty small. Why? Osmosis.

Pure water makes the bears swell up, but salt water keeps them pretty small. Why? Osmosis. (Rachel Feltman/)

Welcome to PopSci’s at-home science projects series. On weekdays at noon, we’ll be posting new projects that use ingredients you can buy at the grocery store. Show us how it went by tagging your project on social media using #popsciprojects.

Gummy bears are delicious. That’s not up for debate (though you’re welcome to eat a few to prove the hypothesis). But they’re also the perfect critters to help demonstrate a process that makes life as we know it possible: Osmosis.

Believe it or not, osmosis also happens when you drop gummy bears into water, revealing the most basic inner workings of your body’s cells. Just add water and a spoonful of salt to see it happen before your eyes.

Stats

  • <b>Time: </b>5 minutes of prep, and 3 to 9 hours of waiting
  • <b>Difficulty:</b> Easy

What you’ll need

  • Gummy bears, preferably dark in color
  • Three small bowls
  • Water
  • 2 tablespoons of salt
  • A spoon
  • Ruler (optional)
  • Kitchen scale (optional)

Instructions

1. Fill two of your bowls with cool water. Room temperature is fine, but keep away from hot water—it’ll melt your gummy bears.

2. Add the salt to the first bowl. The second should just contain water.

3. Plop one gummy bear into each bowl. Make sure they’re fully submerged. Leave the bowls somewhere they won’t be disturbed. Gummy bears are tempting—even when they’re salty and soggy!

Note: We tried different types of gummies (including the sour kind coated with mouth-puckering crystals), and we came to the conclusion that the ideal gummy bears for this experiment are dark in color and chewy instead of soft—just the classic gummy bear. A darker color will not dilute so much as to turn the gummy bear totally clear as it absorbs water, and the thicker gelatin mixture will make the candy less likely to fall apart when you take it out for observation. Also, stay away from sour gummies and those with unusual flavor additives, since they are less likely to yield the intended results.

4. Set aside a third gummy as your experimental control. We recommend you do this before you even think about eating the rest of your gummy bears. It’d be tragic to suddenly realize you ate them all and you no longer have a control for your experiment. Keep it dry.

5. Wait for three hours.

6. Check back in on your waterlogged candies. You can scoop them out with a spoon and observe them on a paper towel if you so choose, but be sure to return them to their proper bowls. Take note of how the gummies have changed—write down your observations so you can contrast them with the end results. You can check in again after the next three hours.

Optional: If your little experimenters need more of a challenge, you can have them measure the bears with rulers and/or kitchen scales, and calculate just how much size and mass the bears have lost or gained.

7. Wait another six hours. The full transformation should be complete around hour nine.

8. Retrieve your bears from their bowls. Use a small spoon and line them up on a plate or paper towel to see how much they’ve changed. The gummy in plain water should be much larger than the unsoaked candy, while the salted water should have kept its bear roughly the same size—unless it’s caused it to shrink. More on that later.

9. Fill a third bowl with cool water and a tablespoon of salt. Place the expanded, waterlogged gummy bear into it and observe it every few hours. It should get noticeably smaller as it soaks.

How it works

Osmosis is the movement of water through a semipermeable membrane—that is, a material with holes large enough to let some things in, but small enough to keep others out. In this process, water moves through the membrane without force or energy, to make water concentration versus other molecules roughly the same on either side.

This process is important in keeping us alive. The outer membrane of our cells is semipermeable and allows small molecules like water and oxygen to pass through while keeping all the cell’s organelles protected and in place. When it’s time to eliminate waste, the cell will start pushing the toxic molecules out, while absorbing water from our blood through osmosis. Once the cell has balanced its water concentration to the one outside of it, it will stop taking in more liquid, thus preventing the cell from bursting.

Gummy bears are made of gelatin and sugar, and the proteins that make up gelatin are very similar to the outer membranes of our cells. Just like them, the gummy bear’s gelatin “skin” will allow water and other small molecules to pass through while keeping larger ones contained—in this case, those larger molecules are the sugar that make gummy bears taste so good.

When you place a gummy bear into water, the sugar molecules will try to spread out and disperse evenly through the water bowl. But the gelatin membrane won’t let them out. That sugar also makes the gummy have a relatively low concentration of water compared to the liquid around it. Osmosis seeks to correct this imbalance, so water will keep pushing into the gummy and through the membrane until the concentration is the same on either side of the gelatin. This means your gummy is going to absorb lots and lots of water.

In one of our trials, extremely salty water actually made a bear shrink! From left to right: A salt-soaked bear, a dry gummy bear, and two bears soaked in water.

In one of our trials, extremely salty water actually made a bear shrink! From left to right: A salt-soaked bear, a dry gummy bear, and two bears soaked in water. (Rachel Feltman/)

In a solution of water and salt, the bowl and the bear have similar water concentrations, so the candy may stay about the same size or even shrink, if the water is salty enough. Just as the sugar in the bear lowers its water concentration, the salt in the bowl means a lower ratio of water to other molecules. As a response, the bear may push out water in order to dilute the liquid inside the bowl. If you place the water-swelled bear into a salt solution, those extra water molecules will leave the bear to lower the salt concentration in the bowl.

If you have time (and gummies) to spare, you can elaborate on this experiment by testing different salt concentrations. You can line up several bowls with increasing quantities of salt in the same amount of water. The more salt you add, the more your candy should shrink.

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