What it shows
Oil and water do not mix, but a drop of detergent makes oil spread into tiny droplets. Bile salts in the small intestine do the same job to fat, so that enzymes can work on it faster.
The science
Fat is digested by the enzyme lipase, which works only at the surface of a fat droplet. Bile, made in the liver and stored in the gallbladder, contains bile salts that act as emulsifiers: one end of each molecule likes water and the other likes fat. They break big fat globules into tiny droplets, called emulsification, which greatly increases the surface area for lipase to act on. Detergent works in the same way in this model.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Two clear glass jars with lids (or test tubes with stoppers)
- Water
- Cooking oil
- A few drops of liquid dishwashing soap
- A dropper
- A spoon
- Food colouring or turmeric powder to colour the oil
- A stopwatch and a torch or magnifier
Safety
For this project: Do not taste anything. Keep the soap away from the eyes and wash hands after the work. An adult must supervise the use of food colouring.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Pour 100 ml of water into each jar and label them A and B.
Colour two spoons of cooking oil with a pinch of turmeric and add a spoonful to each jar.
Add five drops of dishwashing soap to jar B only, as the bile model.
Cover both jars and shake each one for 10 seconds, the same for both, as if the intestine is churning.
Place both on the table and start the stopwatch. Note how the oil looks in each, large blobs or tiny droplets.
Record the time for the oil to separate into a layer in each jar, for up to 10 minutes.
Compare the sizes of droplets by holding up a torch or looking with a magnifier.
Draw a diagram showing a big fat globule with a small surface area, then many small droplets with a large surface area, and add the bile and lipase labels.
What you should see
Jar A separates into a clear oil layer within a minute or two, while jar B stays as a cloudy milky mixture of tiny droplets for much longer.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What does bile do in digestion?
It breaks big fat globules into small droplets, called emulsification.
02Does bile contain an enzyme?
No, it has bile salts and pigments, and the enzyme lipase comes from the pancreas.
03Where is bile made and stored?
Made in the liver and stored in the gallbladder.
04Why is surface area important?
More surface means more places for enzymes to touch the fat and digest it faster.
Take it further
Repeat with different amounts of soap and plot the time for separation against the number of drops.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Biology Models Guide
Make the heart, lungs, kidney, eye, cell and more, and explain them well
Science projects
Science Projects for Class 9 and 10
Models and experiments for high-school physics, chemistry and biology
Find out more about biology
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.