Question

Read the following description of Tube #4:

Tube #4 contains:

Bromothymol blue (BTB)
Carbon dioxide
Not exposed to light
No Elodea present
Initially yellow-green in color
After 24 hours, Tube #4 is still yellow-green in color. Which of the answer choices below describes why?

A. Tube #4 is still yellow-green in color because the carbon dioxide was absorbed.

B. Tube #4 is still yellow-green in color because it performed photosynthesis.

C. Tube #4 is still yellow-green in color because it was unable to perform photosynthesis.

D. Tube #4 is still yellow-green in color because carbon dioxide was released.

Answer 1

The best answer choice that describes why Tube #4 remains yellow-green in color after 24 hours is:

C. Tube #4 is still yellow-green in color because it was unable to perform photosynthesis.

**Explanation:** In Tube #4, there is no Elodea present, meaning there are no plants to perform photosynthesis, which would typically convert carbon dioxide into oxygen and glucose, and in the process, consume carbon dioxide. Since the conditions do not allow for photosynthesis, the carbon dioxide remains in the tube, and without the photosynthetic activity of the Elodea, the pH indicators (like Bromothymol blue) do not change, thus maintaining a yellow-green color.