Bromothymol blue is an indicator that can be used to determine the effects photosynthesis and cellular respiration. as more co2 is added, it turns yellow. when more o2 is added, it turns blue. a plant is placed in water while a student blows bubbles into the water with bromothymol blue. the water turns yellow. after 15 minutes, the water returns to a blue-ish color. how more o2 added, causing the water turn back to blue?