What is bromothymol blue and how is it used to detect cellular respiration?

Bromothymol blue is a pH indicator that changes color in response to variations in acidity. In the context of cellular respiration, it is used to detect the production of carbon dioxide (CO2) by living organisms, which lowers the pH of a solution. When CO2 is produced, it reacts with water to form carbonic acid, leading to a color change in bromothymol blue from blue (alkaline) to yellow (acidic). This visual change indicates that cellular respiration is occurring and producing CO2.