Question

In a lab investigation designed to demonstrate one aspect of photosynthesis, three test tubes were treated as shown above. The test tubes were then placed under a bright lamp for 24 hours. Which of the following is the best explanation for the observed color change in tube 2 ?

• A. The light bleached the solution from its original color of yellow to blue
• B. The aquatic plant produced carbon dioxide, which changed into carbonic acid and caused the color change
• C. The aquatic plant used carbon dioxide, raising the pH of the solution
• D. The plant produced oxygen during photosynthesis, which caused the color change

Answer 1

The correct option is C The aquatic plant used carbon dioxide, raising the pH of the solution

Bromothymol blue is a pH indicator. During photosynthesis, the aquatic plant used carbon dioxide, raising the pH of the solution. Due to change in pH, the colour of bromothymol changes from yellow to blue.