The main aim of this experiment is to investigate how varying the concentration of an enzyme will affect the activity of the enzyme trypsin in milk.

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The main aim of this experiment is to investigate how varying the concentration of an enzyme will affect the activity of the enzyme trypsin in milk.


Enzyme + Substrate                                             Product (s) + Enzyme.

Background Knowledge.

Enzymes are biological catalysts; therefore they speed up the rate of reaction in cells. Enzymes have a tremendous effect on biochemical reactions, and these reactions would take place at a very slow rate if it weren’t for these enzymes.

Basically an enzyme is a catalyst that speeds up reactions faster tan they would normally be at. Enzymes are proteins and are made up of a long chain of Amino Acids. These amino acids are strung together like beads on a necklace, and they are then folded to make very complicated shapes and sizes. Each chemical reaction has its own specific enzyme that controls it. Therefore, only a single enzyme is used to speed up that reaction.

A basic summary of enzymes’ characteristics.

i) Catalysts-         Substances that speed up chemical reactions. These reactions do not change the catalyst. So, even small amounts of an enzyme can do a big job.

ii) Protein-        Whose chemical; shape is special to the substance it works on.

iii) Specific-         Protein alone fits into the chemical shape of the enzyme; protease’, not starch or anything else. So, protein alone is digested by it.

iv) Temp. Sensitive-         Boiling destroys enzymes by altering their shape, cooling only slows down their reaction.

v) pH Sensitive-        Each enzyme has its own preferred (optimum) pH.

The enzyme that we are going to be using is called ‘Trypsin’ and it is a protease enzyme. It digests a protein called ‘casein’

Casein is what makes the milk become opaque. In our experiment we will add trypsin, and this enzyme will break down/ digest the casein into Amino acids, consequently the milk will become clear. This process happens because the casein is broken down/ digested into amino acids, which are soluble in water causing the solution to become cloudy.


For this experiment I will have 3 different variables.

  1. INDEPENDENT variable- this is a variable that cannot be changed under any measures. In this experiment, it is the concentration of the enzyme solution.

  1. DEPENDANT variable- this is the variable which is most affected by the independent variable. In this experiment, it is the rate of reaction.


  1. CONTROLLED variable- these variables will be explained in the fair test section.

Below is a list of possible variables to consider.

  • The temperature of the Reaction
  • PH of the solution. The higher the pH of the Buffer you add to the milk, the quicker the reaction shall take place.
  • Substrate concentration. This will involve using the 4% milk provided, and possibly diluting it with distilled water to produce varying sets of concentrations.
  • Enzyme concentration. This will involve using the 1% trypsin provided. Again, I could possibly dilute the 1% trypsin to various concentrations/ molarities.

I will only be keeping 1 independent variable. (i.e. I will only be changing one variable), and that is the concentration of the enzyme, which in this experiment is trypsin (1%). I have chosen to keep the independent variable of the experiment as the concentration of the enzyme because, to change/vary the concentration of the trypsin (1%) provided is very easy and can be done (with precaution) very easily and accurately.

The Preliminary Experiment

Apparatus used:

  • Enzyme solution (1% trypsin)
  • Milk (4%)
  • Measuring Cylinder
  • Beaker
  • Bench mat
  • Test tubes
  • Test tube rack
  • Distilled water
  • Sticky labels
  • Stop watch


  1. Firstly we set up the experiment, using the apparatus above
  2. We then drew out a simple table in which the results could be easily recorded.
  3. We poured 5 cm3 (as accurately as possible) of 1% enzyme solution into the test tube. We next poured out 15 cm3 (as accurately as possible) of Milk (4%) into a separate test tube.
  4. We then got the stopwatch ready, and as soon as the two solutions were poured into a single test tube, we started the stopwatch and commenced the experiment.
  5. During the course of the experiment we constantly shook the test tube to make sure that the solutions were in proper contact at all times.
  6. This action was carried out until we could see a black ruler clearly through the test tube (i.e. until the solution became clear/transparent.)
  7. Once the experiment was finished we stopped the stopwatch, recorded the time and poured the solutions into the sink.
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Diagram of apparatus used.

What did each test tube contain?

Test tube 1 contained enzyme and milk to a ratio of 1:1

Test tube 2 contained enzyme and milk to a ratio of 1:2

Test tube 3 contained enzyme and milk to a ratio of 1:3

Test tube 4 contained enzyme and milk to a ratio of 1:4


What do the results show?

As you can see, using the ...

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