Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.
- Do not use pipettes for any other purpose.
1) Place 6 test-tubes in a rack, and label them 1-6.
2) Using a single 3ml pipette (twice) put 6 ml of alkaline milk into tubes 1-6.
3) Using a single (smaller) pipette, add 0.5 ml phenolphthalein into tubes 1 to 5 BUT NOT 6.
4) Using a single different pipette, add 1 ml bile salts into tubes 1 , 2, 3 and 6 ONLY.
5) Using yet another pipette, add 1 ml lipase into tubes 1, 2, 4 and 6 ONLY.
6) Record the colours of the contents of the tubes in the table below - in the row labelled "colour at start".
7) Transfer tubes 2-6 to a water bath at 37 °C, and leave them for some time. In the meanwhile, you have the opportunity to carry out the test procedure overleaf which will tell you more about these substances.
8) At regular intervals examine the tubes and look for signs of colour changing from pink to whitish. Record the final colours of the contents of the tubes in the table below - in the row labelled "colour at end ".
|RESULTS||colour at start||pinkish||pinkish||pinkish||pinkish||pinkish||whitish|
|colour at end||whitish||whitish||pinkish||whitish||pinkish||whitish|
Which of the "contents "above is not normally found in the human small intestine?
What is meant by the term lipolytic ?
> breaking down fats (lipids)into simpler substances
What is meant by the term emulsifying ?
> breaking (fat) droplets into smaller ones
Why do you think that the milk was made alkaline before the experiment? (2 reasons)
> because lipase acts in the
alkaline conditions of the intestine
> when the fatty acids are produced, they neutralise the alkali and cause the indicator to change colour
Whereabouts in the body is lipase produced, i.e. Which organ makes it?
Whereabouts in the body is lipase released, i.e Where does it mix with "food" to be digested?
What sort of physical conditions exist there?
>alkaline (warm, wet, etc)
Whereabouts in the body is bile produced, i.e. Which organ makes it?
Whereabouts in the body is bile stored?
> gall bladder
What do you think is the role of bile salts in this experiment?
> to emulsify fat, i.e. make droplets smaller and increase the surface area so as to make it more easily broken down by lipase
Which tube or tubes shows/show a change first?
> 2 ?
What combination of ingredients and conditions do they include?
> lipase, bile salts, warm
Compare the result from this tube with the others. Write your conclusions from this experiment. This should include answers to questions such as:
What does lipase do to the fat in milk? What other factors are needed?Are they absolutely necessary?
> In order to break down fats into fatty acids, lipase needs warmth etc, and bile salts speed it up, but are not essential.
Pour about 10 ml of sodium (or potassium) hydroxide into a boiling tube.
CARE! Wear eye protection when handling alkalies.
Add about 1 ml of copper sulphate solution; the colour should change to a deeper blue. Mix carefully. This is biuret reagent.
Place about 2.5 ml of each substance to be tested into a tube in the rack.
To each add about 2.5 ml of the blue mixture (biuret reagent) produced above.
Wait for a different colour to develop, compared with the leftover untouched mixture.
|Test substance||Resulting colour||Conclusion : substances present|
What is your general conclusion from these tests?
>The enzymes lipase and amylase are/contain protein - also milk is a protein