Question

A group of students are examining both photosynthesis and respiration by the aquatic plant Elodea. A piece of an Elodea plant is placed in a solution of water containing the pH indicator bromothymol blue. Bromothymol blue is different colors at various pH ranges as shown in the table.



Color of Bromothymol Blue at Various pH Ranges

pH Range Color
above 7.6 blue
below 6.0 yellow
between 6.0-7.6 green


When CO2 is produced, carbonic acid forms in the solution causing the pH to become more acidic. When CO2 is consumed, carbonic acid levels decrease, and the pH becomes more basic.



Which TWO effects will photosynthesis and respiration have on the solution containing the Elodea?



A.
The solution will look yellow when Elodea is respiring because it is using CO2.

B.
The solution will look blue when Elodea is respiring because it is producing CO2.

C.
The solution will look yellow when Elodea is respiring because it is producing CO2.

D.
The solution will look blue when Elodea is photosynthesizing because it is using CO2.

E.
The solution will look yellow when Elodea is photosynthesizing because it is using CO2.

F.
The solution will look blue when Elodea is photosynthesizing because it is producing CO2.

Answer 1

Correct answers: C and D.

Explanation: Respiration produces CO2, which forms carbonic acid and lowers pH → bromothymol blue turns yellow (C). Photosynthesis consumes CO2, reducing carbonic acid and raising pH → bromothymol blue turns blue (D).