Final answer:
The stationary phase of bacterial growth is when the rate of cell multiplication equals the rate of cell death, leading to a constant number of live cells. Contrarily, the log phase exhibits exponential cell growth, and the death phase sees an overall decline in cell numbers due to increased mortality over cell division. Penicillin is most effective during the log phase, as bacterial cells are actively dividing.
Step-by-step explanation:
The phase of the bacterial growth curve in which the rate of multiplication equals the rate of cell death is called the stationary phase. In this phase, the total number of live cells reaches a plateau because the number of cells dividing is equivalent to the number of cells dying. The onset of the stationary phase is typically due to factors such as depletion of nutrients, accumulation of waste products, and depletion of oxygen, which limit cell growth.
The lag phase is characterized by cells adapting to their new environment and not changing in number, whereas the log phase shows exponential cell division and an increase in cell number. The death phase, on the other hand, occurs when the rate of cell death exceeds the rate of cell division, leading to a decrease in the total number of cells.
During the log phase, cells are most susceptible to antibiotics like penicillin, which inhibit cell-wall synthesis, because this is the period when bacteria are rapidly dividing and building new cell walls.