Background Information
Yeast is a fungi
Formula
Yeast is able to respire in Glucose because the shape of its active site matches the shape of the Glucose molecule. This type of reaction where a molecule is broken down into smaller pieces is called an Anabolic Reaction.
Apparatus.
1. 250 cm3 Glass Beakers
2. Glass Thistle Funnel
3. Graduated Measuring Cylinder
4. Cork Borer
5. 250 cm3 Glass Cylinders.
6. Digital Stop clock
7. Scalpel
8. Glucose solutions of different concentrations
9. Plastic rule.
10. Safety Goggles.
11.yeast
Method
To test out how the concentration of Glucose affects the rate of reaction first set up the apparatus and prepare the different concentrations of Glucose as below:
1. Using the cork borer, take a sample of potato, cut this piece in cm intervals using the scalpel and plastic rule. Then cut these a further 2 sections, so there is now 5 sections per 1cm piece of potato. Using distilled water; allow the potato discs to stick to the side of the glass Thistle Funnel.
2. Fill a beaker with about 4cm of the pre-made measured solution of Glucose and using the graduated measuring cylinder, completely fill the 10 cm3 cylinder with the same solution.
3. Immerse the thistle funnel into the beaker with the steam below the surface of the Glucose over the funnel stem.
4. Measure the volume of oxygen evolved in a time of 5mins.
5. Repeat the procedure with the other Glucose solutions. Be aware not to contaminate each solutions with one another, this will cause inaccurate results.
6. Repeat all he tests at least three times (Time dependent) so that an average can be obtained. Repeating the experiments several times will help to produce better and more accurate results, as any inaccuracies in one experiment should be compensated for by the other experiments. Note all the results in a table such as the one below.
This gives the rate in cm3 of oxygen produced in the time of 5 minutes, this is because I am timing how much oxygen gas is given off in the space of 5 minutes for the various concentrations of Glucose.
From these results, a graph can be plotted with concentration on the x-axis and the volume of gas released on the y-axis.
To ensure this experiment is completed as fairly as possible, all the variables except for the concentration of Glucose must be kept the same for all experiments. Variables that must not be altered include:
Temperature
- Yeast Concentration
- Dimensions of potato
- Air pressure
Humidity.
When measuring the volumes of water and Glucose, the measurement should be taken from a 90-degree angle to avoid parallax error.
Predictions
I predict that as the substrate concentration increases, the rate of reaction will go up at a directionally proportional rate until the solution becomes saturated with the substrate Glucose. When this saturation point is reached, then adding extra substrate will make no difference.
The rate steadily increases when more substrate is added because more of the active sites of the enzyme are being used which results in more reactions so the amount of Oxygen released in a given time is higher. Once the amount of substrate molecules added exceeds the number of active sites available then the rate of reaction will no longer go up. This is due to the maximum number of reactions being done at once, so any extra substrate molecules have to wait until some of the active sites become available.
