Final answer:
The correct option in the final answer is A. The regulation of the lac operon is important because it helps bacteria conserve energy by preventing the production of enzymes for lactose metabolism unless lactose is present and there is a need to metabolize it as an alternative energy source.
Step-by-step explanation:
The regulation of the lac operon is important in bacteria because there is no energy benefit to expressing lac operon genes when lactose is absent (Option A). The presence of lactose induces the operon to turn on, allowing E. coli to use lactose as an energy source when glucose is not available. This ensures that the cell conserves energy by not producing enzymes for lactose metabolism unless lactose is present to serve as an alternative carbon source. When lactose is not present, a repressor protein binds to the operator, blocking transcription and preventing the unnecessary production of these enzymes.
The lac operon is a typical inducible operon that is active only under specific conditions - when glucose levels are low and lactose is available. This regulatory mechanism is efficient for the cell, as it avoids the energy costs associated with synthesizing unnecessary proteins. Lactose serves not only as an inducer for the operon but also as a substrate for the enzymes produced from the lac operon genes, optimizing the bacterial cell's metabolic flexibility and energy utilization.