American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

If an incubator runs out of carbon dioxide for 6 hours, what change in the media would be expected?

1. The media will turn clear

2. pH is lower in the media

3. pH is higher in the media

4. The media turns a yellow color

The correct answer is: pH is higher in the media

When an incubator runs out of carbon dioxide (CO2) for an extended period, such as 6 hours, the environment within the incubator becomes more alkaline. CO2 is a key component in maintaining the pH balance of cell culture media. Under normal conditions, the presence of CO2 contributes to the formation of carbonic acid, which helps to maintain an appropriate pH level. Without sufficient CO2, the buffering capacity of the media is disrupted, leading to a decrease in carbonic acid formation. This results in an increase in pH, making the media more alkaline. Therefore, during this situation, one would expect the pH of the media to be higher, which can be confirmed by observing that other indicators (such as phenol red, a common pH indicator in culture media) typically shift color from red (neutral pH) towards pink or violet as the pH increases. In contrast, lower pH (a more acidic environment) would not be expected due to the absence of CO2. Additionally, changes in color to a yellow hue may indicate a more acidic environment than before, which would not be a direct result of CO2 depletion, as acidosis is not induced simply by the absence of CO2 alone