Bromothymol blue (BTB) is a pH indicator that is also used to detect carbon dioxide (CO). BTB is blue
when pH is basic and CO is low. BTB is yellow when pH is acidic and Co, is high. BTB is green when
pH is neutral. A group of students are planning to perform an investigation in which they will place
either a stalk of the aquatic plant elodea or a snail in a test tube that contains water with a neutral
pH of 7 and BTB. The students will also include a test tube that contains elodea and a snail. Observing
color change once the tubes have been placed under a growth light for several hours will allow the
students to answer which TWO of the following questions?
A. Do both elodea and snails require oxygen to survive?
B. Does elodea produce oxygen during photosynthesis?
C. Do snails respire faster when placed in a tube with elodea?
D. Do snails use the Co, produced by elodea to produce oxygen?
E. Does photosynthesis performed by elodea remove Co, from the water?
F. Does cellular respiration occur at a higher rate than photosynthesis in the tube with only elodea?