Final answer:
Penicillins and cephalosporins inhibit the enzyme transpeptidase, which is essential in peptidoglycan synthesis of bacterial cell walls, causing the cells to burst.
Step-by-step explanation:
Penicillins and cephalosporins block enzymes that cross-link the glycan molecules, interrupting the completion of the cell wall. The correct answer is C. Peptidoglycan synthesis. These antibiotics function by inhibiting the enzyme transpeptidase, which is critical for the last steps of bacterial cell wall synthesis. This inhibition prevents the formation of peptide crosslinks in the peptidoglycan layer, leading to weak cell walls that cannot withstand osmotic pressure, consequently causing the bacterial cells to burst.