Measuring how much CO2 the reaction produces we could know how well the enzyme is working with a substrate, checking thus its specificity. Materials: 5 Ignition tubes Pipette Glucose Maltose Sucrose Lactose Yeast Cotton wool Test tubes Stop watch Ruler Variables: Independent variable: substrate (glucose, starch, maltose, lactose, sucrose), enzyme (yeast), volume of substrate, volume of enzyme. Dependent: volume of CO2 released (measured in mm) Controlled variables: Temperature, pressure, time.
Method: 1- Fill 5 ignition tubes, half with yeast (2.0 ml) and half with each corresponding substrate (2.0 ml), using a pipette. 2- Quickly after the mixture is done, place the ignition tubes upside down in a test tube, helping yourself with a pen. 3- Start the stop watch once the ignition tube is upside down in the test tube, and measure the space left (this will be time 0) 4- Place some cotton wool on the top of each test tube in order to block oxygen, and therefore, for anaerobic respiration to occur.
5- Prepare one mixture with the yeast (enzyme), and with water, to act as a control. Treat the control in the same way you have done it with the samples. 6- As anaerobic respiration occurs, CO2 is released displacing the mixture of yeast and substrate into the test tube. Measure the amount of CO2 released during 20 minutes, taking a reading of the empty space inside the ignition tube every 5 minutes. 7- Repeat the experiment 3 times for statistical purposes.