Cellular Respiration Evidence

Respiration Procedures

Procedure 1:

1. Mix ¼ tsp of yeast into 175 mL of warm (40-43 C) water in a 250 mL beaker. Stir until dissolved.
2. Label the big and small test tubes 1-5.
3. In a 250 mL beaker, mix the 1 gram packet of Equal with 100 mL of water. In another 250 mL, mix the 1 gram packet of Splenda with 100 mL of water. In another 250 mL beaker, mix half of the 4 gram packet of sugar with 200 mL of water.
4. Fill the smaller test tubes with 15 mL solution as follows:
 Tube 1: 1% glucose solution
 Tube 2: 1% sucrose solution
 Tube 3: 1% Equal solution
 Tube 4: 1% Splenda solution
 Tube 5: 1% sugar solution

5. Then, fill each tube to the top with the yeast solution.
6. Slide the corresponding larger tube over the small tube and invert it as practiced. This will mix the yeast and sugar solutions.
7. Place respirometers in the test tube rack, and measure the initial air space in the rounded bottom of the internal tube. Record these values in Table 1.
8. Allow the test tubes to sit in a warm place (~37 C) for one hour.
9. At the end of the respiration period, measure the air space in the internal tubes, and record in Table 1.

Table 1: Gas production
Tube Initial gas height (mm) Final gas height (mm) Net change
1 7 mm 8.5 mm 1.5 mm
2 7 mm 9 mm 2 mm
3 5 mm 5 mm 0 mm
4 4 mm 4 mm 0 mm
5 5 mm 6 mm 1 mm

Questions

1. Hypothesize why some substances were not metabolized, while others were. Research the chemical formula of Equal and Splenda and explain how it would affect respiration.
2. If you have evidence of respiration, Identify the gas that was produced. Suggest two methods for positively identifying this gas.
3. How do the results of this experiment relate to the role yeast plays in baking?
4. What would you expect to see if the yeasts' metabolism was slowed down? How could this be done?
5. Indicate sources of error and suggest improvement.

Procedure 2:

1. Fill two beakers with 200 mL water.
2. Soak 50 pinto beans in Beaker 1P and 50 kidney beans in Beaker 1K for 24 hours.
3. Empty the water from beakers 1P and 1K.
4. Pour the soaked beans onto paper towels, keeping them separated.
5. Label the remaining beakers: Beakers 2P, 3P, Beaker 2K, and 3K.
6. Place several layers of moist paper towels at the bottom of the 250 mL beakers.
7. Place 50 pre-soaked pinto beans into beaker 1P, 50 control pinto beans in Beaker 2P, and zero beans in Beaker 3P.
8. Place 50 pre-soaked kidney beans into beaker 1K, 50 control kidney beans in Beaker 2K, and zero beans in Beaker 3K.
9. Dispense 4 mL of bromothymol blue solution into each of the six measuring cups, and place a measuring cup inside each beaker.
10. Stretch Parafilm across the top of each beaker. Secure with a rubber band to create an airtight seal.
11. Place the beakers on a shelf or table, and let sit undisturbed at room temperature.
12. Observe the jars at 30 minute intervals for three hours, and record any color change of the bromothymol blue in Tables 2 and 3.
13. Let the beans and the jar sit overnight. Record your observation in Tables 2 and 3.

Table 2: Bromothymol blue color change over time for pinto bean experiment
Time Beaker with pre-soaked beans Beaker with un-soaked beans Beaker with no beans
0 min blue blue blue
30 min Slightly green blue blue
60 min Light green blue blue
90 min Light green blue blue
120 min Light green blue blue
150 min Light green blue blue
180 min Light green blue blue
24 hours Light green Bluish green blue

Table 3: Bromothymol blue color change over time for kidney bean experiment
Time Beaker with pre-soaked beans Beaker with un-soaked beans Beaker with no beans
0 min blue blue blue
30 min Slightly green blue blue
60 min green blue blue
90 min green blue blue
120 min green blue blue
150 min green blue blue
180 min green blue blue
24 hours green Bluish green blue

Questions

1. What evidence do you have to prove cellular respiration occurred in beans? Explain.
2. Were there differences in the rates of respiration in pinto beans vs. kidney beans? If so, why?
3. If this experiment were conducted at 0 C, what difference would you see in the rate of respiration? Why?
4. What is the mechanism driving the bromothymol blue solution color change?
5. What are the controls in this experiment, and what variables do they eliminate? Why is it important to have a control for this experiment?
6. Would you expect to find CO2 in your breath? Why?
7. What effect would large changes in temperature (e.g., 37 C vs. 45 C) have on respiration in beans? Design an experiment to test your hypothesis, complete with controls.