Describe in complete sentences the cellular environment (s) that would turn the operon ""on.""

Inducer or the ligand

Explanation:

The operon is a sequence of genes present on the DNA which is controlled by the single promoter and are activated or switched on only when required otherwise switched off.

The Operon system is influenced by the molecule present in the environment called the ligand or the inducer like lactose which when binds to the repressor molecule changes the confirmation of the repressor molecule as a result of which the repressor molecule is released from the operator site and the operon is turned on.

Thus, inducer or ligand is correct.