A biology class is studying cellular respiration. They set up an experiment containing four flasks. Each flask is the same size, 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?

Flask Number Contents of Flask

1 1 plant

2 2 goldfish

3 1 plant and 2 goldfish

4 Nothing

A. Flasks 1 and 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.
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.
D. Flask 2 (only) because the fish produce CO2 as products of cellular respiration and do not undergo photosynthesis therefore not consuming CO2.
I got A, is this correct?