Imagine that scientists have discovered an industrial pollutant that modifies the structure of a cell cycle checkpoint protein such that it loses its function. Cultured human cells exposed to this molecule divide at a rate double that of untreated cells. Based on these data only, one could conclude that the chemical is.

Carcinogenic

Explanation:

A carcinogenic substance is able to modify or damage the genome in a way which promotes the formation of cancerous cells. Cell cycle checkpoint proteins are very crucial for the progression of normal cell cycle. They check for any anomaly in their designated step and halt the process if it is detected. Repair mechanism is activated and cell cycle does not progress till the damage has been repaired.

Here, the pollutant alters the structure of these proteins such that they lose their function. They are not be able to stop cell cycle from progressing even if there is some damage in the genome. The cell divides and gives rise to more damaged cells. Eventually these cells lose their normal function and just keep dividing due to which their division rate becomes double of the normal rate. It can ultimately give rise to cancer which is why the chemical is carcinogenic.