Since carbon dioxide dissolves in water to form an acid, an acid-base indicator such as bromthymol blue is used to track the acid concentration during plant photosynthesis and respiration. Bromthymol blue turns yellow in an acid solution and remains blue in a basic solution. The color change is reversible. A student used the following procedure to track carbon dioxide.
In an experiment, a student placed a solution of bromthymol blue into each of two flasks, inserted a drinking straw in each flask, and blew through the straw until the solution turned from blue to yellow. Carbon dioxide, a waste product in the student’s breath, caused the color change. The student then placed a small Elodea water plant in each flask and closed the flasks with rubber stoppers. Flask A was placed in bright sunlight, while flask B was placed in the dark for 24 hours, as shown in the figure below.
After 24 hours, the bromthymol blue in flask A had turned back to blue, while in flask B it was still yellow.
What relationship was the experiment designed to explore?
The relationship between light and:
A . the color of bromthymol blue
B . amount of liquid in the flask
C . the rate of photosynthesis
D . plant production of water
E . plant consumption of carbon dioxide
Answer: E
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