8th Grade Lab Science (Cribb & Duane)

MATERIALS

PROCEDURE

1.   Prepare a water bath for the yeast. A water bath is simply a large beaker of water at a certain temperature. This ensures that the yeast will remain at a constant and controlled temperature. To prepare the water bath, obtain some warm and cool water from your teacher. Combine the warm and cool water into the 600-mL beaker until it reaches 38 – 40°C. The beaker should be filled with about 300 – 400 mL of water. Leave the thermometer in the water bath during the course of the experiment to monitor the temperature of the water bath.

2.   Obtain four test tubes and label them G, S, F, and L.

   3.   Obtain the four sugar solutions: glucose, sucrose, fructose, and lactose.

a.    Place 2 mL of the glucose solution in test tube G.

b.    Place 2 mL of the sucrose solution in test tube S.

c.    Place 2 mL of the fructose solution in test tube F.

d.    Place 2 mL of the lactose solution in test tube L.

4.   Obtain the yeast suspension. Gently swirl the yeast suspension to mix the yeast that settles to the bottom. Put 2 mL of yeast into each of the four test tubes. Gently swirl each test tube to mix the yeast into the sugar solution.

5.   Set the four test tubes into the water bath.

6.   Incubate the test tubes for 10 minutes in the water bath. Keep the temperature of the water bath constant. If you need to add more hot or cold water, first remove as much water as you will add, or the beaker may overflow. Use a beral pipet to remove excess water. While the test tubes are incubating, proceed to Step 7.

7.   Plug the CO₂ Gas Sensor into Channel 1 of the LabPro or CBL 2 interface. Use the link cable to connect the TI Graphing Calculator to the interface. Firmly press in the cable ends.

8.   Turn on the calculator and start the DATAMATE program. Press  to reset the program.

   9.   Set up the calculator and interface for a CO₂ Gas Sensor.

a.    If the calculator displays CO2 GAS (PPM) in CH 1, proceed directly to Step 10. If it does not, continue with this step to set up your sensor manually.

b.    Select SETUP from the main screen.

c.    Press  to select CH 1.

d.    Select CO2 GAS from the SELECT SENSOR menu.

e.    Select parts per million (PPM) as the unit.

f.      Select OK to return to the main screen.

10.   When incubation is finished, use a beral pipet to place 2 mL of the sugar/yeast solution into the 250-mL respiration chamber.

11.   Place the shaft of the CO₂ Gas Sensor in the opening of the respiration chamber. Gently twist the stopper on the shaft of the CO₂ Gas Sensor into the chamber opening. Do not twist the shaft of the CO₂ Gas Sensor or you may damage it.

12.   Wait one minute, then select START to begin data collection. Data will be collected for
5 minutes.

13.   When data collection has finished, a graph of CO2 GAS VS. TIME will be displayed. Press  to return to the main screen.

14.   Remove the CO₂ Gas Sensor from the respiration chamber.

15.   Fill the respiration chamber with water and then empty it. Make sure that all yeast have been removed from the respiration chamber. Thoroughly dry the inside of the respiration chamber with a paper towel.

16.   Use a notebook or notepad to fan air across the openings in the probe shaft of the CO₂ Gas Sensor for 1 minute.

17.   Perform a linear regression to calculate the rate of respiration.

a.    Select ANALYZE from the main screen.

b.    Select CURVE FIT from the ANALYZE OPTIONS menu.

c.    Select LINEAR (CH 1 VS TIME) from the CURVE FIT menu.

d.    The linear-regression statistics for these two lists are displayed for the equation in the form:

Y=A*X+B

e.    Enter the slope, A, as the rate of respiration for the sugar tested in Table 1.

f.      Press  to view a graph of the data and the regression line.

g.    Press  to return to the ANALYZE menu.

h.    Select RETURN TO MAIN SCREEN from the ANALYZE menu.

18.   Repeat Steps 10 – 17 for each of the sugar solutions.

19.   When all sugars solutions have been tested, select QUIT from the main screen to exit the DATAMATE  program.

DATA

PROCESSING THE DATA

1.   On the chalkboard, record the respiration rates for each of the sugars you tested. When all other groups have posted their results, calculate the average rate of respiration for each sugar. Record the average rate values in Table 2.

2.   Using graph paper or Graphical Analysis, plot a bar graph of all four sugars tested. Place the respiration rates recorded in Table 1 along the y-axis, and sugar tested along the x-axis.

QUESTIONS

1.   Considering the results of this experiment, do yeast equally utilize all sugars? Explain.

2.   Hypothesize why some sugars were not metabolized while other sugars were.

3.   Why do you need to incubate the yeast before you start collecting data?

4.   Yeast live in many different environments. Make a list of some locations where yeast might naturally grow. Estimate the possible food sources at each of these locations.