What it shows
Food travels through one long tube, the alimentary canal, and is broken down by chewing and stomach juices, then absorbed in the small intestine. The model shows the order and lengths of the parts.
The science
Digestion has two parts. Mechanical digestion is chewing and churning, and chemical digestion uses enzymes in saliva, stomach juice and the small intestine to change big food molecules into small soluble ones. The small intestine is several metres long (textbooks give about six) and folded, which gives a large area for absorbing nutrients into the blood. The large intestine absorbs water.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An old stocking or long sock for the intestine
- A zip bag for the stomach
- A wide plastic tube or a rolled plastic sheet (about 2 cm across) for the food pipe
- A cardboard body outline
- A cardboard roll or thick paper tube for the large intestine
- Cooked rice, a little curd and water as soft food
- Glue, tape, scissors and marker
- A tray to work on
Safety
For this project: An adult must help with cutting. Wash your hands after touching the food mixture and do not eat it afterwards. Throw the used mixture away the same day.
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.
Draw the outline of a body on a large piece of cardboard and mark the mouth, chest and belly.
An adult cuts two small holes in the zip bag, one at the top for the food pipe and one at the bottom corner. Fix the wide plastic tube from the mouth down to the top hole with tape.
Attach the open end of the stocking to the bottom hole of the stomach as the small intestine and coil it into the belly area.
Glue the cardboard roll at the end of the stocking as the large intestine and show an exit point.
Mash the rice with curd and water in a cup to make a soft, runny food mixture.
Pour it into the food pipe a little at a time and squeeze the stomach gently as a churning action.
Squeeze the mixture along the stocking to show peristalsis; some liquid will seep through the net of the stocking into the tray, which stands for absorption.
Label each organ and write one line about its job beside it.
What you should see
The soft mixture travels from the mouth tube to the stomach bag and through the stocking, showing the path and relative length of the digestive tract.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What is peristalsis?
The wave of muscle squeezing that pushes food along the canal.
02Where is most food absorbed?
In the small intestine.
03What does the large intestine do?
It absorbs water and forms waste.
04Why is the small intestine so long and folded?
To give a large surface for absorption.
Take it further
Measure about six metres of string and see how it fits inside a body outline when coiled.
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
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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.