Final answer:
The trp operon in E. coli is repressible and can be turned off by the presence of tryptophan, while the lac operon is inducible and activated in the presence of lactose.
Step-by-step explanation:
In the E. coli bacteria, the lac operon and the trp operon utilize their respective repressor proteins to regulate gene expression, but function in different ways based on environmental conditions. The trp operon is considered repressible, meaning it is generally active but can be turned off in the presence of sufficient levels of the amino acid tryptophan. When tryptophan binds to the trp repressor, the complex then attaches to the operator, shutting down transcription. Conversely, the lac operon is considered inducible, as it is generally inactive but can be activated in the presence of lactose, which acts as an inducer by binding to the repressor and preventing it from attaching to the operator. This allows the operon to transcribe the genes needed for lactose metabolism especially when glucose levels are low. Therefore, the most accurate description of these operons is that 'B. The trp operon is repressible while the lac operon is inducible.'