Question

The inducer for switching on the lac operon in bacteria is

• A. Presence of lactose
• B. Number of bacteria
• C. Presence of structural genes in the bacteria
• D. Presence of sucrose
• E. Presence of RNA polymerase

Answer 1

Answer: (A)

Presence of lactose

Lactose: Regulatory gene produces a repressor and which goes to bind the inducer to form a repressor-inducer complex. This complex when fails to join the operator gene, results in gene expression of these three genes, metabolizing lactose to galactose and glucose. Hence, lactose acts as an inducer for its breakdown. Thus, the correct answer is option A.