Carbon Dioxide and Green Blue

Experiment 2: Aerobic Respiration in Beans
We will evaluate respiration in beans by comparing carbon dioxide production between germinated and nongerminated beans. As shown in the balanced equation for cellular respiration, one of the byproducts is CO2 (carbon dioxide):
C6H12O6 + 6 H2O + 6 O2 → energy + 6 CO2 + 12 H2O
We will use a carbon dioxide indicator ( bromothymol blue) to show oxygen is being consumed and carbon dioxide is being released by the beans. Bromothymol blue is an indicator that turns yellow in acidic conditions, green in neutral conditions, and blue in basic conditions. When carbon dioxide dissolves in water, carbonic acid is formed by the reaction:
H2O + CO2 → H2CO3 resulting in the formation of this weak acid. If an indicator such as bromothymol blue is present, what do you think would happen? (Hint - what color would the indicator change to?)
Materials
(6) 250 mL Beakers
24 mL Bromothymol Blue Solution, C27H28Br2O5S
100 Kidney Beans
6 Medicine Cups (small, clear, plastic cups)
15 cm Parafilm®
Permanent Marker
100 Pinto Beans

1 Pipette
6 Rubber Bands (Large. Contains latex; please handle with gloves if you have a latex allergy.)
*Water
*Paper Towels

*You Must Provide

Procedure:
1. Label two of the 250 mL beakers as Soaked: Pinto and Soaked: Kidney.
2. Fill each beaker with 200 mL water.
3. Count and transfer 50 pinto beans into the Soaked: Pinto beaker. Then, count and transfer 50 kidney beans into the Soaked: Kidney beaker. Allow the beakers to rest for 24 hours.
4. After 24 hours have passed, carefully strain the water from each beaker.
5. Place two paper towels on a flat work surface. Use the permanent marker to label one paper towel as Soaked: Pinto and the second as Soaked: Kidney.
6. Pour the soaked beans onto paper towels, keeping them sorted by bean type.
7. Label the remaining beakers as Dry: Pinto, No Pinto, Dry: Kidney, and No Kidney.
8. Place several layers of moist paper towels at the bottom of all six, 250 mL beakers.
9. Place 50 pre-soaked pinto beans into the Soaked: Pinto beaker, 50 unsoaked pinto beans into the Dry: Pinto beaker, and no beans into the No Pinto beaker.
10. Place 50 pre-soaked kidney beans into the Soaked: Kidney, 50 unsoaked kidney beans into the Dry: Kidney beaker, and no beans into the No Kidney beaker.
11. Dispense four mL of bromothymol blue solution into each of the six measuring cups. Then, place one cup inside each beaker (Figure 5).
12. Stretch Parafilm® across the top of each beaker. Secure with a rubber band to create an air-tight seal. Note: If your Parafilm® seal breaks, plastic wrap (such as Saran® wrap) can be used as a replacement.
13. Place the beakers on a shelf or table, and let sit undisturbed at room temperature.
14. Record the initial color of the bromothymol solutions and observe the jars at 30 minute intervals for three hours. Record the color of the bromothymol blue in Tables 2 and 3.
15. Let the beans and the jar sit overnight. Record your final observations in Tables 2 and 3.
Table 2: Bromothymol Blue Color Change Over Time for Pinto Bean Trial
Time
Pre-Soaked Pinto Beans
Dry Pinto Beans
No Pinto Beans
0 min Blue
Blue
Blue
30 min Bluish green Blue Blue
60 min Dark 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 Yellow Blue Blue

Table 3: Bromothymol Blue Color Change Over Time for Kidney Bean Trial
Time
Pre-Soaked Kidney Beans
Dry Kidney Beans
No Kidney Beans
0 min Blue Blue Blue
30 min Turqoise/green Blue Blue
60 min Light green
Blue
Blue
90 min Lime green Blue Blue
120 min Lime green Blue Blue
150 min Lime green Blue Blue
180 min Very Lime Green Blue Blue
24 hours Yellow Blue Blue