The Measurement of CO2 Production from Yeast Respiration

Procedure:

1. Obtain a 15ml centrifuge tube. It should have three very small holes in the cap.

2. Partially fill a small beaker (no larger than 250 ml) with warm water. Stabilize the temperature between 35 - 40 degrees C.

3. Add 8 ml of sugar solution (5% sucrose) to the tube.

4. Keeping the cap upright, put the tube in your beaker of warm water. Keep it there for 5 minutes.

5. Now fill the centrifuge tube tube with 7% yeast solution until the tube is full. Continue to fill until the liquid is over the rim, but avoid spilling if possible.

6. Screw on the cap securely. A few drops of yeast solution will exit the small holes. This is normal.

7. Mix by inverting the tube several times, keeping your finger over the holes to prevent loss of fluid. Also confirm that the tube has no sizeable air bubbles. (A small one is acceptable).

8. Now invert the tube in your beaker of warm water. Start timing. Keep the beaker between 35 and 40 degrees for the duration of the lab. (The tube will begin to leak yeast solution out of the holes.)

9. At the end of the first three minutes, mark the bottom point where there are carbon dioxide bubbles. Include any foam as CO2. Use a wax marker.

10. Continue to take readings every 3 minutes until 30 minutes have elapsed. Mark each spot where the CO2 is found, being careful not to erase previous marks. Invert the tube once to remix the contents every third reading. Don't forget to plug the holes with your finger.

11. After you complete the experiment, record the ml of each marking on the tube. Rinse out your tubes. For markings of less than 2 ml, you can find an accurate value by using a 2 ml pipet to fill the centrifuge tube to that point and reading the value on the pipet.

Analysis

1. Using a graphing calculator, (TI 82, 83 or 85), name two lists. The first List CO2 will be used for the volume of CO2 collected. The second list, time will record when each reading was taken. Make sure each CO2 value corresponds to the correct time reading.

2. Make a scatter plot of the data with CO2 volume on the y-axis and time on the X-axis. Which value is dependent variable? Independent?

3. Enter your results into the classroom graphing calculator. Again, make sure the value for each time reading is directly across from the corresponding

To see the growth curve follow these directions (For TI-83)

Enter the values for time in L1, the corresponding values of CO2 in L2 (or name each list)

Push 2nd, Stat Plot, and turn on Plot 1. Make sure other plots are off.

Choose the scatter plot (The first entry under Type.)

The X list is L1 (or whatever you named your time list)

The Y list is L2

Next: STAT, CALC, LOGISTIC, L1, L2, VARS, Y-VARS, FUNCTION, Y1, ENTER, ENTER At this point it will take a while to calculate the curve - be patient! When done ZOOM 9 and your scatter plot should be displayed with the log growth curve.