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Choose an experiment:

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Rates - Colorimetry
Amylase
Aquarium
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Lipase & fat
Food energy
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Lipase and fat - Measuring the rate of the enzyme lipase 
Fats, such as the fats in milk, need to be digested by your body. They are broken down into fatty acids and glycerol by an enzyme called lipase. You can do this in the lab if you mix lipase and fat together and measure the pH, or acidity, of the mixture. data logger with a pH sensor and electrode to take the readings for us.  

The chemicals you need

Connect two pH sensors to the data logger. 

One possible setup

Pour 5 cm3 of milk into each of  two boiling tubes. The pH will be roughly neutral, add sodium carbonate solution until both milks are pH 8.5 - 9. We do this because the enzyme works better in alkali. Then add a drop of bile (washing up detergent - see picture) to one tube, add  5cm3 lipase to both tubes, stir and place the tubes in a water bath. Leave for 30 minutes 


One possible result and a very good one.

Here is a good result - collected by a couple of beginners - very lucky ones at that. Join in the fun and answer these questions*

a) why is one graph different from the other? Try to explain the shape of the graphs?

b) why are the starting points of the graphs similar? 

c) why are the ending points of the graphs similar? 

d) what can you say about the closeness of the starting points of the graphs? 

e) what do you think about this idea: we used the software to subtract 0.2 pH units from every point on the red line. Here is the result, shown on a new brown line:

Result after applying twiddle factor

A variation of the experiment is to use different strengths of lipase suspension - in fact the chemicals illustrated above. Here is the result of measuring two tubes - 1% and 2% lipase. Which line is which below:   

Another good result from St John's in Leatherhead - the graph scales have been greatly magnified for the photograph hence the noisiness. The software shown is PASCO Data Studio used with a Science Workshop 500 interface.   

Your turn: if you have some data logging software you ought to be able to analyse the data from our experiment.

lipase.sid - right click to download this SID (CSV) file into your data logging software.

lipase.csv - right click to download this CSV file into your software (e.g. for Excel)

lipase.txt - right click to download this TAB delimited file (e.g. for PASCO Data Studio)

 

Activities in this section adapted from The IT in Science book of Data logging and Control. © IT in Science and may be reproduced as needed for use within your school.

 

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