When both glucose and lactose are added to the growth medium, Escherichia coli will have a growth curve that
A) does not change.
B) grows slowly and then, halfway through, grows faster.
C) grows, levels off, and then grows again.
D) grows more slowly than with glucose alone.
E) grows more quickly than with glucose alone.

Question

Quizplus · Accepted Answer

When both glucose and lactose are present, E. coli preferentially uses glucose first due to catabolite repression. Once glucose is depleted, the bacteria then start to metabolize lactose, leading to a biphasic growth curve where growth levels off as the bacteria switch from glucose to lactose metabolism, and then resumes.

When Both Glucose and Lactose Are Added to the Growth