What it shows
The inside of the small intestine is covered with finger-like villi that give it a very large surface area for absorbing food. A looped towel soaks up much more water than a flat cloth of the same size, just as a villus-lined gut absorbs more.
The science
The small intestine is about 6 metres long, and its inner wall is folded and covered with millions of tiny villi, each with microvilli. This increases the surface area to roughly the size of a tennis court, so digested food passes into the blood quickly. Each villus has a network of capillaries and a lacteal. A looped towel acts the same way: the loops expose more surface to the water, so more is taken up.
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.
- A flat piece of cotton cloth, 10 cm by 10 cm
- A piece of terry towel, 10 cm by 10 cm
- Water with a few drops of food colour
- A kitchen scale that reads to 0.1 g
- A shallow dish
- A timer
- A notebook
- String or a long cloth strip for the small intestine length model
Safety
For this project: An adult must cut the cloth and supervise the scissors. Keep the scale dry.
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.
All the safety rulesStep 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.
Weigh the dry flat cloth and the dry terry towel, and write their masses.
Pour 100 mL of coloured water into the dish.
Dip the flat cloth fully for 10 seconds, lift it by a corner and let it drip for 10 seconds.
Weigh the wet cloth and subtract the dry mass to find the water absorbed.
Repeat for the terry towel, using the same dipping and dripping times.
Do each test three times and calculate the average water absorbed by each cloth.
Show your results in a bar chart and compare the absorption per piece.
On a card, sketch the lining of the small intestine with villi and label the capillary, lacteal and the absorbed food.
What you should see
The looped towel holds much more water than the flat cloth of the same size, showing how extra surface area increases absorption. The sketch links this to villi.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What are villi?
Tiny finger-like folds in the small intestine that absorb digested food.
2Why does a large surface area help absorption?
More of the digested food touches the wall at once, so more is absorbed per second.
3What carries the absorbed glucose away?
The blood in the capillaries of each villus.
4Why was the same dipping time used?
To keep the test fair.
Take it further
Measure the length of the wrinkles in a folded cloth against a flat cloth to calculate how folding increases the area.
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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