This fun, but gross, practical gives children a model of some of the processes that go on in our bodies when we digest our food.

What you need

Each group of children will need:

• 1/3 banana,
• 1 cream cracker,
• Paper cup with hole in the bottom,
• 50ml water,
• Clear vinegar,
• plastic sandwich bag,
• scissors,
• one leg cut from a pair of tights (or a stocking),
• paper towels,
• A plastic, paper or aluminium tray or bowl

What will you do?

• This will be messy, so you might want to cover the table with paper first.
• Pour 50 ml of clear vinegar into the plastic bag. The bag plays the role of the stomach, and the vinegar models the stomach acid.
• Break up the cream cracker and drop it into the bag.
• Break up lumps of the banana and drop them into the bag.
• Add 50 ml of water into bag to mimic saliva from your mouth.
• Squeeze the air out and seal the bag,
• Smash up this mixture with your hands for 2 or 3 minutes, this will turn the mix into a soup. This mimics the action of the stomach muscles in churning up the food.
• Tilt the bag up slightly and cut a small hole in one corner of the bag. (The corner where you’re not tipping the soup towards!)
• With the stocking held low over the tray/bowl (very important) squeeze the contents of the bag into the stocking (Which is modelling the small intestine).
• Squeeze the food through the stocking, keep squeezing the stocking to let the liquid run out.
• Eventually, cut the toe off the stocking and squeeze the waste food out into the plastic/paper cup (large intestine)
• if you can, push the waste food through the bottom of the cup onto the tray (to model going to the toilet).

Extension

You can take this experiment further and add a few squirts of different coloured food colouring to the food to mimic some of the digestive juices from the gall bladder, pancreas etc. This can also help give the waste a browner colour if you want to go for added realism!

This video I filmed for Twig Education a few years back shows what should happen.

And I’ve just added this video to YouTube too.

What will they see?

As the children carry this out, try to get them to think about what the various parts of the model is trying to represent.

They should be able to see how food turns into a soup-like liquid in the stomach (the plastic bag) which then passes into the intestines (the stocking). Within the small intestine nutrients and water pass through the wall.The liquid that ends up in the tray should be milky, which shows how the useful chemicals the body needs have passed through the wall. The large chemicals, such as fibre stay inside the intestine and are eventually passed out when we go to the toilet.