Answer: the cell wall and are especially useful in controlling gram-positive bacteria
Penicillin is a group of drug/antibiotic that works by inhibiting the formation of cross-link of the peptidoglycan. Peptidoglycan is a protein that commonly found in bacteria cell wall, but it was much thicker in gram-positive bacteria. Since the drug disrupt the production of material that responsible for cell wall, it will weaken the membrane and induce lysis.
