The antibiotic penicillin can kill invading bacteria without harming human cells because it targets bacterial :

Penicillin is a beta-lactam antibiotic that kills bacteria by specifically targeting the bacterial cell wall. Its mechanism involves inhibiting the synthesis of peptidoglycan, a structural polymer that provides strength and rigidity to the cell wall. Penicillin binds to enzymes called penicillin-binding proteins (PBPs) that cross-link peptidoglycan chains.

• Selective Toxicity: Human (animal) cells do not possess a cell wall; they only have a plasma membrane. Furthermore, humans do not produce peptidoglycan. This allows penicillin to destroy bacteria without affecting human cells.
• Lysis: When the cell wall is weakened, the high internal osmotic pressure causes the bacterial cell to burst (lysis).
• Other Options: Ribosomes (C) are targeted by antibiotics like tetracyclines, while plasma membranes (B) are targeted by polymyxins. Penicillin does not interact with chromosomes (D).