In the $lac$-operon model,lactose molecules function as:

Wild-type $E. coli$ cells are grown in a normal medium containing glucose. They are then transferred to a medium containing only lactose as the sugar source. Which of the following changes will occur?

Which of the following statements is incorrect regarding the $lac$ operon?

Given below are two statements:
Statement $I$: In lac operon,the repressor protein binds to the promoter region of the operon and prevents $\text{RNA}$ polymerase from transcribing the operon.
Statement $II$: Regulation of lac operon can also be visualized as regulation of enzyme synthesis by its substrate.
In the light of the above statements,choose the correct answer from the options given below:

In the $lac$ operon,which enzyme$(s)$ will be produced in the cell if there is a nonsense mutation in the $lac$ $y$ gene?

What is the first level of regulation of gene expression in eukaryotes?