Final answer:
In the presence of penicillin, a bacterial cell dies because it undergoes lysis. Penicillin prevents bacteria from forming strong cell walls, leading to their swelling and bursting when in hypotonic environments. The correct answer is option b.
Step-by-step explanation:
Penicillin is an antibiotic that works by interfering with the synthesis of cell walls in bacteria, specifically targeting the enzyme responsible for the final step in building the bacterial cell wall. Because of this action, bacteria in the presence of penicillin are susceptible to lysis, which is the breaking down or bursting of the cell wall due to osmotic pressure. Without the protective structure of the cell wall, bacterial cells absorb water, swell, and ultimately lyse because they cannot maintain their structural integrity. This mechanism does not affect human cells because they do not have cell walls but rather have cell membranes.
In a hypotonic environment, where there is a higher concentration of water outside the cell than inside, a cell that lacks a rigid cell wall, like a bacterial cell influenced by penicillin, will absorb water, swell, and eventually lyse. In a hypertonic environment, cells lose water and shrivel, but in this case, bacterial cells would typically have undergone lysis before this could happen due to the prior damage to the cell wall.
Therefore, in the presence of penicillin, a cell dies because (b) it undergoes lysis.