Final answer:
The E. coli lac operon is inducible and requires lactose for activation while being repressed in the presence of glucose, unlike the ara operon which is activated by arabinose and regulated by the AraC protein.
Step-by-step explanation:
A major difference between the E. coli lac and ara operons is that the lac operon is an inducible operon while the ara operon is also an inducible operon but primarily involved in the metabolism of arabinose. The lac operon is unique because it requires the presence of lactose and the absence of glucose to be activated. The lac operon's regulation includes both a repressor, which inhibits transcription in the absence of lactose, and an activator, which promotes transcription when glucose levels are low, indicating lactose should be metabolized. Conversely, the ara operon is controlled by the AraC protein and is activated in the presence of arabinose. This specific differentiation in response to environmental sugars allows E. coli to efficiently adapt its metabolism to the available nutrients.