Enzyme Activity Lab

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Name:	________________________________	Date:	___________
Teacher:	________________________________	Period:	___________

Aim
To investigate the rate of an enzyme-controlled reaction under varying environmental conditions.

Materials
regular test tubes, colorimeter test tubes, a Spec 20 colorimeter, diluted turnip extract (1 mL of extract per 200 mL of water), guaiacol, distilled water, a stopwatch, hydrogen peroxide (H₂O₂), and a micropipette

Overview
When guaiacol and hydrogen peroxide mix in the presence of peroxidase (an enzyme found in turnips), guaiacol is oxidized and becomes a dark color. The Spec 20 colorimeter measures a change in a solution's transmittance (how well light can travel through the solution). A lower number on the Spec 20 colorimeter indicates that the transmittance of the solution has decreased, so it has become darker. By measuring the rate at which a solution's transmittance changes, you can determine the rate of the enzyme-catalyzed reaction occurring in the test tube.

Procedure

1. Fill a colorimeter test tube with distilled water. Place this test tube in the Spec 20 colorimeter and adjust the readout so that it displays a 100% transmittance.
2. Prepare four regular test tubes with the following: .2 mL of H₂O₂, .01 mL of guaiacol, and 4.7 mL of distilled water. Label these three test tubes A, B, C, and D.
3. Place 1 mL of diluted turnip extract in a colorimeter test tube with 4 mL of water. Label this tube 1. Add the contents of tube A to tube 1. Immediately place tube 1 in the colorimeter and start the stopwatch. Record the transmittance of the solution ever 20 seconds for two minutes.
4. Place .5 mL of diluted turnip extract in another colorimeter test tube with 4 mL of water. Label this tube 2. Add the contents of tube B to tube 2. Place tube 2 in the colorimeter and again record the transmittance every 20 seconds for two minutes.
5. Repeat this procedure for test tube 3 (which contains 2 mL of turnip extract) and test tube 4 (which contains 1 mL of briefly boiled turnip extract).

Observations
Record the data you gathered in the table below.

Transmittance of solutions
	0s	20s	40s	60s	80s	100s	120s
Tube 1
Tube 2
Tube 3
Tube 4

On a piece of graph paper, graph the data in this chart. Note the slope of the graph for each of the solutions. This is in indicator of how fast the reaction proceeded.

Questions

1. In which tube did the reaction proceed at the slowest rate?    ________________
   
   
2. In which tube did the reaction proceed at the fastest rate?    ________________
   
   

Conclusions
In the space below, explain exactly what caused the differences in reaction rates for each tube.

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Sources of Error
Identify any possible sources of error which may have affected the results of this experiment.

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