What likely caused media in the incubator to turn magenta and result in cell death?

The correct answer relates to the critical balance of carbon dioxide levels in the incubator, which directly influences the pH of the media. When CO2 levels are too low, there is an insufficient formation of carbonic acid in the media. This process leads to an increase in pH, making the media alkaline. Many cell types are sensitive to pH changes, and an alkaline environment can disrupt metabolic processes, resulting in cell death.

The observation of magenta coloration in the media indicates a change in pH, as many pH indicators, such as phenol red, change color based on the acidity or basicity of the solution. A magenta color often suggests that the environment has become too alkaline, corroborating the idea that low CO2 levels may have contributed to this issue.

In this context, excessive humidity generally would not lead to a change in media color or significantly affect cell viability in the same way that pH shifts do. Similarly, while both inadequate temperature control and high CO2 levels can impact cell growth, neither would typically cause the specific symptoms described, such as media turning magenta and resultant cell death.