Final answer:
The lac operon in E.coli regulates genes that code for enzymes required for the breakdown of lactose. The lac operon is A) an inducible operon that is activated in the presence of lactose. The correct answer is A) An inducible; lactose.
Step-by-step explanation:
This means that the lac operon is only transcribed and expressed when lactose is present in the cell. The lac operon encodes the genes necessary to acquire and process lactose from the environment, breaking it down into glucose and galactose.
The lac operon is also subject to activation in the absence of glucose. When glucose levels are low or non-existent, the cAMP-CAP protein complex serves as a positive regulator to induce transcription of the lac operon. This ensures that the lac operon is only activated when glucose is scarce and lactose is available.
In conclusion, the correct answer is A) An inducible; lactose. The lac operon is an inducible operon that is activated in the presence of lactose, allowing E. coli to utilize lactose as an energy source when glucose is limited.