Question

All organisms are dependent on a healthy carbon dioxide-oxygen balance. Photosynthesis and cellular respiration are key processes in maintaining this balance. Your class is conducting a lab experiment to investigate the relationship between photosynthesis and cellular respiration by observing how carbon dioxide cycles through a biological system. To conduct the experiment, each group set up four test tubes containing 30 ml distilled water and 3 ml of bromothymol blue. Bromothymol blue is a pH indicator that changes from blue (alkaline) to yellow (acid). When carbon dioxide dissolves in water, it produces carbonic acid, turning the indicator from blue to yellow. The level of CO2 was inferred from a change in the indicator color.

A snail, elodea (aquatic plant), or both were added to the tubes and they were stoppered. Tubes were placed under a grow light for 24 hours and the results recorded. The test tubes were then covered for 24 hours to produce a dark environment and the results recorded. Which statement best explains the change in Test Tube D from the light setup to the dark setup.
A) The rate of photosynthesis decreased in the dark, thus the elodea used less CO2. The elodea and snails produced less CO2 through cellular respiration, causing the CO2 to be in equilibrium, making the solution more neutral (yellow).
B) The rate of photosynthesis decreased in the dark, thus the elodea used less CO2. The elodea and snails continued to produce CO2 through cellular respiration, raising the level of CO2 in the tube, causing the solution to become more acidic (yellow).
C) The rate of photosynthesis decreased in the dark, thus the elodea used more CO2. The elodea and snails continued to consume CO2 through cellular respiration, lowering the level of CO2 in the tube, causing the solution to become more basic (yellow).
D) The rate of photosynthesis decreased in the dark, thus the elodea used less CO2. The elodea and snails continued to consume CO2 through cellular respiration, raising the level of CO2 in the tube, causing the solution to become more acidic (yellow).
Eliminate

Answer 1

Test Tube D showed more acidity (yellow color) in the dark setup due to the decrease of photosynthesis in the absence of light, while respiration continued, resulting in higher CO₂ levels and an acidic environment.

Step-by-step explanation:

The correct answer to explain the change in Test Tube D from the light setup to the dark setup is B) The rate of photosynthesis decreased in the dark, thus the elodea used less CO₂. The elodea and snails continued to produce CO₂ through cellular respiration, raising the level of CO₂ in the tube, causing the solution to become more acidic (yellow).

In the presence of light, elodea performs photosynthesis, utilizing CO₂ and releasing O₂. At the same time, both elodea and the snail respire, which consumes O₂ and produces CO₂. However, during the dark, photosynthesis does not occur because light is a necessary component for the process of photosynthesis. Nevertheless, both organisms continue to respire in the dark, contributing to the increase in CO₂ levels that leads to a more acidic environment indicated by the yellowing of the bromothymol blue solution.

Answer 2

The correct answer would be option B

The rate of photosynthesis in the plants during the dark(night) slows down but the process of cellular respiration does not depends on the light to take place.

The snail and the plant produced carbon dioxide by the process of cellular respiration at night but it was not consumed by the plants by the process of photosynthesis.

Due to this, carbon dioxide got accumulated in the solution and turned the solution more acidic ( solution turned from blue to yellow).