Question

The pH indicator bromothymol blue turns yellow when CO2 gas is added to a solution and blue when CO2 is removed from a solution. An experiment will test how the intensity of light affects the rate of photosynthesis in algae. Which of these should be a control for this experiment?
A. Algae that are placed in a yellow solution and keep in the direct sunlight.

B. Algae that are placed in a blue solution and kept in direct sunlight.

C. Algae that are placed in a yellow solution and kept in the dark.

D. Algae that are placed in a blue solution and kept in the dark.

Answer 1

Answer:

The correct answer would be C. Algae that are placed in a yellow solution and kept in the dark.

In a scientific experiment, a control is a variable which is kept constant or unchanged throughout the experiment.

The results of other variables are compared with the control.

It increases the reliability of an experiment.

In the above experiment, algae must be kept in dark in order to prevent photosynthesis and thus, it prevents the utilization of carbon dioxide.

Similarly, the yellow color solution would also act as control as it would help in observing if any carbon dioxide is utilized from the solution. The utilization or removal of the same would convert the solution blue in color.