Yeast lab. Question: how does the yeast concentration affect the rate of anaerobic respiration?? Measured by the concentration of released CO2.

Equipments and procedure:

Equipments:

• PASCO GLX with (CO2 sensor).
• 200 ml, 3 % sucrose solution.
• Variety of yeast solutions (g/ml) (2%,4%,6%,8% and 10%).
• Cylinder.
• Beaker (200 ml).
• Plastic cover.

Procedure:

• Prepare at least 5 different concentrations of yeast (2%, 4%, 6%, 8% and 10%)
• Solutions were prepared by mixing different percentages of yeast with water, one hour before initiating the experiment.
• Prepare 3% sucrose solution.
• Place 3% sucrose solution in the beaker.
• Start by adding 10 ml of 2% yeast suspension, inside the beaker containing sucrose, after shaking the solution (it is better to start by least yeast concentrations then most).
• Place CO2 sensor inside the beaker (as shown in the apparatus).
• Put the cover on the beakers opening (preferably fast),and wait for the one minute interval (while shaking the solution, when GLX is taking the reading).

Record the reading after the time has ended (the CO2 censor was calibrated at the beginning and the data collection settings was modified to collect CO2 concentration in ppm for 1 minute intervals.)

• Empty the beaker and clean it, before repeating the previous procedure.
• Repeat the same procedure for every concentration, 3 times for every single concentration and then obtain the average.
• Record the results in a proper table.
• Represent results in an explanatory graph.

Data collection and processing:

Raw data:

Table (1): initial and final readings of  CO2 evolved for every yeast concentration

Processed data:

1. The average difference was calculated by the following equation:

2. The difference between the final and initial weights was calculated by:

3. The ppm uncertainty , was given by the GLX company or provider.

Table (2): the difference between the initial and final readings CO2 evolved for every yeast concentration

The previous data can be represented by the following graph:

Graph (1): the CO2 yield vs. the yeast concentrations

Conclusion and evaluation:

Conclusion:

1. From the previous tables and graph, the results show that, as yeast concentration increases, which means that the anaerobic respiration rate increases, and thus the hypothesis is proved right.

Evaluation:

1. A problem was faced in taking volumes, since cylinders were the instrument used, which is a way of error.
2.  The cover provided didn't it the opening of the cylinder, thus producing errors.
3. Shaking the solution while reading, differed in the intensity, form one solution to the other.

Possible improvements:

1. Use more accurate equipment (pipettes and burettes…. Etc) to take the volumes of yeasts and sucrose.
2. Use an automated machine that does vibration, to make the whole intensity of shaking equal.
3. Use containers or cylinders, which have proper openings for the CO2 sensor, to get more accurate results.
4. Use another apparatus, where the sucrose will be put into a syringe, the syringe attached to a tube, which goes through the test tube, where the yeast will be put, and the tube contains a proper opening for the CO2 reader, and then when everything is set up sucrose will be pumped by the syringe and the reaction would start.