In the given diagram of the lac operon,which one is the inducer?

In $Escherichia \ coli$,$lac$ operon is induced by

An organism is able to survive on a culture medium containing nutrient $A$ through an enzyme-catalyzed process: $A \xrightarrow{X} B \xrightarrow{Y} C$. $A$ mutant organism fails to survive on this medium. However,it grows when nutrient $B$ is added to the medium. Which gene of this mutant is defective?

Few genes are found in all types of cells of differentiated multicellular organisms of higher classes. These are called:

When do bacteria $NOT$ produce $\beta$-galactosidase?

Who provided the clear explanation of the $Lac$ operon?