Final answer:
The most rapid growth of bacteria occurs in the log phase, where they actively divide and their numbers increase exponentially. This is also the phase where antibiotics such as penicillin are most effective, as bacteria are most vulnerable when they are growing and synthesizing new cell walls. Option b.
Step-by-step explanation:
The Most Rapid Growth of Bacteria
The most rapid growth of bacteria occurs during the log phase(b), which is also known as the exponential growth phase. In this phase, bacteria are actively dividing through binary fission, and their numbers increase exponentially. This phase stands in contrast with the lag phase, where cells prepare for growth but do not increase in number; the stationary phase, where the growth rate slows as resources become limited and the rate of cell division equals the rate of cell death; and the decline or death phase, where the number of live cells begins to decrease as conditions become less favorable for survival.
Effectiveness of Penicillin
Penicillin, an antibiotic that inhibits cell-wall synthesis, would be most effective during the log phase of bacterial growth since this is the stage where bacteria are actively dividing and building cell walls. Therefore, an intervention with penicillin at this stage would disrupt the bacteria's ability to synthesize new cell walls, leading to cell death.