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
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
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
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.