In an investigation of the cycling of environmental gases, a
student placed water and bromthymol blue in each of four test
tubes as shown in the diagrams below. No additional items were
placed in tube 1, a snail was placed in tube 2, an aquatic plant
(elodea) was placed in tube 3, and both a snail and an elodea
were placed in tube 4. The tubes were then stoppered and placed
in bright light for 24 hours.
Tube 1 Tube 2 Tube 3 Tube 4
How would the solution in tube 3 change after 24 hours?
A) It would change from yellow to blue.
B) It would change from blue to brick red.
C) It would contain more oxygen.
D) It would contain less nitrogen.

In an investigation of the cycling of environmental gases, a student placed water and bromthymol blue in each of four test tubes as shown in the diagrams below. No additional items were placed in tube 1, a snail was placed in tube 2, an aquatic plant (elodea) was placed in tube 3, and both a snail and an elodea were placed in tube 4. The tubes were then stoppered and placed in bright light for 24 hours. The solution in tube 3 changes after 24 hours because it would contain less nitrogen.

The dfferent tubes are shown in the picture that I uploaded.