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cell respiration open response question
A student poured a solution of bromthymol blue indicator into three test tubes. Then, he placed an aquatic
plant in two of the test tubes, as shown below. He placed a stopper on each test tube and placed them all in the
dark for 24 hours. Bromthymol blue turns from blue to yellow in the presence of CO2.
Figure 9–4
1. Applying Concepts Look at Figure 9–4. Which process or processes would you expect the organisms in the
test tubes to carry out—cellular respiration, photosynthesis, or both? When would you expect each process to
occur?
2. Predicting Predict what will happen to the test tubes in Figure 9–4 after 24 hours in the dark.
3. Predicting Assume that after 24 hours in the dark, the bromthymol blue in test tubes 2 and 3 in Figure 9–4
had turned yellow. The student then placed test tube 3 in a sunny window. He left test tube 2 in the dark.
Predict what color the solution in each test tube will be after the next 24 hours. Explain your prediction in
terms of cellular respiration and/or photosynthesis.
cell respiration open response question
Answer Section
OTHER
1. ANS:
Sample answer: When exposed to light, the aquatic plants will carry out both cellular respiration and
photosynthesis. After a time in the dark, the plants will carry out only cellular respiration.
2. ANS:
The solution in test tubes 2 and 3 will turn yellow because the plants will give off CO2 from cellular
respiration but will not use it up through photosynthesis.
3. ANS:
After another 24 hours, test tube 2 will still be yellow. Test tube 3 will be blue again.
test tube 2 remained in the dark and was not able to carry out photosynthesis, so it did not use up carbon
dioxide. However, the plant in test tube 3 was in the light, where it could carry out photosynthesis. This plant
used up the carbon dioxide