Bile and emulsification sim
Add bile (or water) to oil, shake and watch the droplets split on a microscope screen, then time lipase turning pink phenolphthalein colourless at 35 °C and plot how the time falls as the surface area grows.
Nutrition in humans: bile and fat digestion · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Bile is made in the liver, stored in the gall bladder and enters the small intestine through the bile duct. Its bile salts emulsify fats: they lower the surface tension of the fat, so it breaks into tiny droplets that stay apart in water (an emulsion). This is physical digestion: the fat is still fat, and bile is not an enzyme. Bile is also alkaline, which helps to neutralise the acid from the stomach, and these alkaline conditions suit lipase (in this tube the effect of bile's alkali is left out). Smaller droplets have a much larger surface area: area = 6V ÷ d (an extension), so halving the diameter doubles it. Lipase, from the pancreas and the small intestine, works at the surface of the droplets, so it digests emulsified fat into fatty acids and glycerol much faster. In this experiment the fatty acids neutralise the sodium carbonate, and the pink phenolphthalein turns colourless when enough has been made. The model: 0.2 cm³ of oil starts as drops about 2 mm across (about 48 of them); each shake with bile halves the droplets' diameter, down to about 2 µm. Shaking alone breaks the oil into smaller drops for a moment, but without bile they join back, to about 1 mm. Lipase's rate rises with the area and levels off: rate ∝ A ÷ (A + 60 cm²), and the pink goes in 2 min × (1 + 60 ÷ A): read to the half-minute, about 12 min with water and about 2.5 min with bile and plenty of shaking. Time moves only when you press Wait. Model limits: the halving per shake, the 60 cm² and the 2-minute scale are illustrative, chosen to match a typical class result; the microscope view shows the droplets' size at ×400 but not their true number; real bile also helps by carrying the fatty acids away in micelles.
- Boiling tube: oil on pink water (sodium carbonate and phenolphthalein)
- Water bath at 35 °C, near body temperature
- Digital microscope screen: the oil droplets at ×400
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
More biology sims
- Iodine: test for starch simAdd iodine solution to the prepared food sample.
- Leaf starch test: follow the method simBoil the leaf in water for about 1 minute, then heat it in ethanol in a water bath to remove chlorophyll.
- Limiting factors simThe rate is set by whichever requirement is in shortest supply.
- Microscope: magnification and focus simTotal magnification is eyepiece magnification multiplied by objective magnification.
- Osmosis: watch the level simA sucrose solution is separated from the surrounding solution by a membrane permeable to water but not sucrose.
- Photosynthesis: prove the conditions simStart with destarched plants, expose matched leaves to the chosen conditions, then test both leaves for starch by the same complete iodine method.