Mr. Miller's biology class is studying cellular respiration. To model cellular respiration, they set up an experiment containing four flasks. Each flask is the same size and are stoppered and placed under a floodlight. Each flask also contains 200 mL of H20 and 2 mL of bromothymol blue. Bromothymol blue is a chemical indicator solution that changes color from blue to yellow in the presence of CO2. The students then place a plant and/or fish into each flask (except for Flask #4 which is the control group) according to the table above. Which flask(s) will turn yellow and why?

Question

Responses
A Flask 1 & 3 because these flasks contain plants that undergo photosynthesis.Flask 1 & 3 because these flasks contain plants that undergo photosynthesis.
B Flask 3 (only) because this is the only flask in which photosynthesis and cellular respiration are both taking place.Flask 3 (only) because this is the only flask in which photosynthesis and cellular respiration are both taking place.
C Flask 1 & 2 because there is only one process taking place in each of these flasks so the products do not get used up.Flask 1 & 2 because there is only one process taking place in each of these flasks so the products do not get used up.
D Flask 2 (only) because the fish produce CO2 as products of cellular respiration and do not undergo photosynthesis therefore not consuming CO2.

Answer 1

The correct answer is B. Flask 3 (only) because this is the only flask in which photosynthesis and cellular respiration are both taking place. In flask 3, the plant undergoes photosynthesis, producing oxygen and consuming carbon dioxide. The fish also undergoes cellular respiration, producing carbon dioxide and consuming oxygen. The presence of both processes in flask 3 will result in the production of carbon dioxide, causing the bromothymol blue indicator to turn yellow.