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 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 test tubes were then covered and 3 ml of bromothymol blue was 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 at 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 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, making 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 solution to become more acidic (yellow). test tube contents: tube a: control; tube b: elodea; tube c: snail; tube d: elodea and snail. initial color: green; light set up: green; dark set up: yellow

Explanation:

In the dark, plants like elodea cannot perform photosynthesis which consumes carbon - dioxide. Instead, they and snails carry out cellular respiration which produces carbon - dioxide. An increase in carbon - dioxide in water forms carbonic acid, making the solution more acidic. Bromothymol blue, a pH indicator, turns yellow in acidic solutions. In Test Tube D with elodea and snail, more carbon - dioxide is produced through respiration in the dark, making the solution more acidic and turning the indicator yellow.

Answer:

D. The rate of photosynthesis decreased in the dark, thus the elodea and snails continued to consume CO₂ through cellular respiration, making the solution more acidic (yellow).