Testing for enzymes

Read our standard health & safety guidance

Lesson organisation

A straightforward class experiment in which the different sources of catalase are tested for their effect on hydrogen peroxide solution. This should take no more than 20 - 30 minutes.

Apparatus and chemicals

Eye protection

Each working group will require:

Conical flasks (100 cm³), 3
Measuring cylinder (25 cm³)
Bunsen burner
Wooden splint

Hydrogen peroxide solution, '5 volume' (Low hazard at this concentration) (see note 1)
Liver (small piece) (see note 2)
Potato (small piece) (see note 2)
Celery (small piece) (see note 2)

Access to:

A bucket or bin for disposal of waste materials

Technical notes

Hydrogen peroxide solution (Low hazard at concentration used) Refer to CLEAPSS Hazcard 50 and Recipe card 32

1 Hydrogen peroxide solution of '5 volume' concentration is low hazard, but it will probably need to be prepared by dilution of a more concentrated solution which may be hazardous.

2 Only small samples of liver, potato and celery are required. These should be prepared for the lesson ready to be used by students. A disposal bin or bucket for used samples should be provided to avoid these being put down the sink.

Procedure

HEALTH & SAFETY: Wear eye protection. Students must be instructed NOT to taste or eat any of the foods used in the experiment.

a Measure 25 cm³ of hydrogen peroxide solution into each of three conical flasks.

b At the same time, add a small piece of liver to the first flask, a small piece of potato to the second flask, and a small piece of celery to the third flask.

c Hold a glowing splint in the neck of each flask.

d Note the time taken before each glowing splint is re-lit by the evolved oxygen.

e Dispose of all mixtures into the bucket or bin provided.

Teaching notes

Some vegetarian students may wish to opt out of handling liver samples, and this should be respected.

Before or after the experiment, the term enzyme will need to be introduced. The term may have been met previously in biological topics, but the notion that they act as catalysts and increase the rate of reactions may be new. Similarly their nature as large protein molecules whose catalytic activity can be very specific to certain chemical reactions may be unfamiliar. The name catalase for the enzyme present in all these foodstuffs can be introduced

To show the similarity between enzymes and chemical catalysts, the teacher may wish to demonstrate (or ask the class to perform as part of the class experiment) the catalytic decomposition of hydrogen peroxide solution by manganese(IV) oxide (Harmful - refer to CLEAPSS Hazcard 60).

If students have not performed the glowing splint test for oxygen for some time, they may need reminding of how to do so by a quick demonstration by the teacher.

Health & Safety checked, April 2008

Web Links

There are many websites from the USA and Canada showing variations of this experiment, most of them relating to classes of older students investigating other factors affecting the rate of decomposition. Some show video-clips of the experiments involved, as well a giving a more detailed theoretical background. One example is:
www.coolschool.ca/lor/BI12/unit7/U07L04.htm

A website from the UK that is pitched at a similar level to this experiment, and then extends the topic in a relatively accessible manner for pre-16 students:
www.crocodile-clips.com/absorb/AC4/sample/LR1506.html

(Websites accessed June 2008)