Lab: Energy Release and Cellular Metabolism

BIOLOGY
CARBON DIOXIDE PRODUCTION
BY
GERMINATING SEEDS

INTRODUCTION:

Living things need energy to carry on most of their processes. The cells of germinating seeds oxidize carbohydrates, in the process known as cellular respiration, to provide energy for growth. In this process, carbon dioxide is released as a byproduct. The balanced equation for cellular respiration (oxidation of glucose) is as follows:

C₆H₁₂O₆ + 6 H₂O + 6 O₂ ---> energy + 6 CO₂ + 12 H₂O

The increasing concentration of carbon dioxide, in a closed environment, can be observed using a pH indicator solution. As carbon dioxide dissolves in water, it produces carbonic acid. As the carbonic acid concentration increases, the pH lowers.

In this lab, you will observe the formation of carbon dioxide by germinating seeds using bromthymol blue solution as the indicator. As more carbon dioxide is absorbed, and the pH lowers, bromthymol blue turns from blue to green to yellow.

MATERIALS:

50 Pea seeds for sprouting
2 one-quart jars with airtight lids
Beaker or small jar to soak seeds
Paper towels
2 test tubes
Bromthymol blue solution
Water

PRE-LAB:

Soak the pea seeds for 24 hours before the lab.

PROCEDURE:

1. Obtain 2 one-quart jars with airtight lids and place several layers of moist paper towels in the bottom of each jar.

2. Place 50 presoaked peas in the first jar. Fill 2 test tubes half full of bromthymol blue solution, and stand 1 tube in each jar.

3. Place the lids on the jars tightly and keep the jars on a shelf or table, undisturbed, at room temperature. Figure 1 shows the test jar, and figure 2 shows the control.

4. Observe the jars each day, and record the color changes of the bromthymol blue on your DATA TABLE. Remember, the observation after the jars are set-up, is for day zero.

DATA TABLE: Carbon Dioxide Production by Germinating Seeds.

Date Jar with Peas
(test jar) Jar without Peas
(control)

Day zero
blue
blue

ANALYSIS:

Question 1. How did the color of the bromthymol blue solution in your test jar change over time?

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Question 2. What can be inferred from the change observed in question 1?

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Question 3. Was there a color change in the control jar (the jar with no seeds)?

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Question 4. What can be inferred from the change observed in question 3?

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Question 5. Why was it necessary to have a control for this experiment?

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Date	Jar with Peas (test jar)	Jar without Peas (control)
DATA TABLE: Carbon Dioxide Production by Germinating Seeds.
Day zero	blue	blue