Question

Read the given passage.

In bacteria -galactosidase (gal) is an enzyme which is used for lactose metabolism. The human intestinal bacteria of three different groups were cultured in a medium containing glucose. At time 1, the bacteria were transferred to media containing lactose as a nutrient source instead of glucose. At time 2, the bacteria were returned to the medium containing glucose. Samples of bacteria were removed at five-minute intervals and tested for the presence of gal. The results are presented by graph.
The induction of gal production by intestinal bacteria in this way is useful because

• A. Humans do not consume foods containing lactose all the time.
• B. It prevents toxic buildup of lactic acid.
• C. The production of gal is harmful to bacteria.
• D. It prevents the bacteria from using glucose as a nutrient source.
• E. Lactose is harmful to bacteria.

Answer 1

The correct option is A Humans do not consume foods containing lactose all the time.

Lac-operon is inducible operon and is transcribed only when lactose is available. It makes the system energy effecient by not making the enzymes when they are not needed. Since human do not consume lactose containing food all time, bacteria must have shut down the -gal production.
So, the correct answer is option A.