If like me you succumb to the pleas of a ‘treat’ and end up buying a ridiculously big bag of some type of jelly sweet, that you really don’t want your kids to eat all of, then this might be an experiment for you. Although for us the actual experiment didn’t work entirely, it was fun to do. Plus it got kid M predicting and taking before and after measurements, which all felt a bit like a ‘real’ experiment.
What you need:
- Jelly worms (essential – you could do it with 2 but a few more make for a better experiment. You could use other jelly sweets but worms are quite good as they are easy to measure).
- Ruler (essential – or anything you can use for measuring).
- Bowls (essential – 2 that will fit a couple of worms).
- Salt (essential – half a teaspoon will do).
- Warm water (essential – 160ml or roughly 2/3 of a cup).
What to do:
- Measure the worms and note down their length.
- Put half the water (80ml) in each bowl. Add the salt to one of them. Give it a good stir until all the salt has dissolved. If the bowls are the same label the one with salt in it.
- Put half the worms in one bowl and half in the other.
- Wait for a few hours…
- Measure the worms again to see if they have changed.
- Get your kids to predict what will happen to the worms.
- Probably best not to use vegetarian jelly sweets like we did as the gelatine is meant to hold the worms together (ours were a bit delicate so not sure veggie gelatine is quite as effective!).
- Don’t eat the worms afterwards, especially the ones in salty water!
The science bit
So what should happen is both sets of worms increase in size. The plain water should be absorbed more than the salt water, making these worms grow bigger but ours both turned out roughly the same size. Not sure what happened with ours but there is every chance that my water was not salty enough due to an error by my little lab assistant (or most probably me!), or it could have been the vegetarian worms.
The reason the worms absorb the water is osmosis (remember that from biology/chemistry lessons at school?). Simply it’s a balance of water molecules, with them moving from an area of higher concentration (the water) to an area with less (the worm).
The book I got this from (which is a fab book) says that this experiment shows that plain water is easier for our bodies to absorb and that is why we don’t drink salt water. Plain water might be easier for our body to absorb but I am pretty sure that isn’t why we don’t drink salt water, or at least not the most important reason. If we did drink salt water (am thinking sea water in particular here) then you would end up weeing out lots of water to flush out all the excess salt, which could lead to dehydration, nausea, muscles cramps, organ failure, oh and eventually death if you kept going…
Explaining it to children
I think this experiment is a good one for getting kids to make predictions. Kid M thought they would shrink in the water, which is a fair prediction as without the gelatine they would eventually dissolve in water. She was a bit too interested in whether she could eat the worms after the experiment to think about what happened. If she had wanted to listen then I would have explained the tiny molecules of water can get in to the worms, making them grow in size. The plain water gets absorbed more than the salty water, so these worms should grow bigger.
(Inspecting them over breakfast. She still wanted to eat them even though it was about 6.30am!)
Experiment based on an activity from the fantastic 101 coolest simple science experiments book.