Fun and easy science experiments for kids and adults.

Gummy bear osmosis

Grow and shrink gummy bears by placing them in water with or without sugar. An experiment about how osmosis affects the cells.

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Video

Materials

3 gummy bears
2 drinking glasses
1 spoon
Sugar
Refrigerator
Something to heat water with (for example a microwave oven or a kettle)

Step 1

Put two of the three gummy bears in a glass of cold water (in hot water they melt).

Step 2

Put the glass in the fridge (otherwise mold will start to grow). Wait for 24 hours and see how the gummy bears have grown!

Step 3

You can now shrink one of them again if you want! Pour a few centimeters (1-1 1/2 in) of boiling hot water in a glass. Dissolve as much sugar as you can (do not use too much water, because then you will need a lot of sugar). When the sugar starts to accumulate on the bottom, you are done. Let the glass cool, for example in a cold water bath (remember, in hot water gummy bears melt).

Step 4

Take one of the swollen gummy bears and place it in the sugar water. Put the glass in the fridge. Put the other swollen gummy bear in an empty glass, and also put it in the fridge.

Step 5

Wait for another 24 hours and see how the gummy bear in the sugar water have shrunk again!

Step 6

Compare your gummy bears.

Short explanation

In this demonstration, a gummy bear acts just like a cell. When it is surrounded by pure water, it absorbs water and swells, but when it surrounded by water with a lot of solutes in it, it gives off water and shrinks.

Long explanation

A cell is bounded by and held together by its cell membrane, a thin membrane only a few molecules thick. Inside the cell membrane is the cell's entire contents, which are mostly water with solutes. The cell membrane is not completely impermeable. It is permeable to some substances, such as water. What determines whether water will migrate out or in through the cell membrane is how full the surrounding water is of other chemical substances. If a cell is surrounded by pure water, water migrates into the cell and it swells. If a cell is surrounded by, for example, salt water or sugar water, water migrates out of the cell and it shrinks. It is important to note that the chemical substances that are dissolved in the water cannot travel through the cell membrane.

What determines which direction the water will travel is whether the water outside the cell contains more or less solutes than the water inside the cell. If the water inside and outside the cell contains the same amount of solutes, equilibrium has been reached and the cell no longer swells or shrinks.

This process, when water travels through a membrane that lets water through but not the chemical substances that are dissolved in the water, is called osmosis.

In fact, it doesn't matter what the solutes are. In this experiment, you used sugar, but you might as well have used salt.

Osmosis is the reason you become dehydrated if you drink salt water. Your cells will then bathe in water that is full of solutes (salt) and water will migrate out of them. The cells shrink and will lack water.

A gummy bear, or other gummy candy, consists mainly of gelatin. Then there's some water in them, as well as sugar and other additives. The gummy bear can, from an osmotic point of view, be seen as water with a whole lot of solutes in it.

The reason why you have to heat water to dissolve sugar in it, is that this makes it a lot faster. This is because the water molecules move faster at high temperature.

Experiment

This is actually already an experiment, but you can keep experimenting. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

How big will a gummy bear be after 1, 2, 4, 6, 12, 24, 48, 72 hours in water?
Does it matter if you cover the glass or not?
Is it possible to shrink a swollen gummy bear completely down to its former size again?
What other things swell in water?
What other things shrink in sugar water?

Variations

If you prefer to work with real cells, you can use raw potato. Make three equally sized potato cubes. Place one in pure water. Place the second in water saturated with sugar. Save the third in some plastic wrap. Put everything in the fridge and wait for 24 hours. The potato cube that's been in pure water will have swelled and the potato cube that's been in sugar water will have shrunk. Compare with the potato cube you saved in the plastic wrap.

From its natural state, a potato cube can be made to both swell and shrink. However, it's difficult to get a gummy candy to shrink from its normal state. To succeed with this, you need to dissolve more sugar (or something else) in the water, than there is gelatin and other dissolved chemical substances in the gummy candy. It's possible, but the difference is hardly noticeable.

So the benefits of using potato cubes are that you work with real cells and that you can both shrink and grow them. The downside is that the difference is not as big as with gummy candies.

Also try other things that consist of cells. Berries or rice, for example, will give you a noticeable difference.