The correct answer to the question is option 1: cell wall formation in bacteria.

Antibiotics are substances that are used to inhibit the growth of or destroy bacteria. Penicillin, specifically, is known as a cell wall synthesis inhibitor.

Bacteria have a cell wall which provides structural support and protection. It is made up of a complex network of peptidoglycan, a substance that gives the cell wall strength and rigidity.

Penicillin works by inhibiting the enzyme responsible for the formation of peptidoglycan, known as transpeptidase. Without transpeptidase, bacteria are unable to build and maintain their cell wall, making them more susceptible to damage and destruction.

By blocking cell wall formation, penicillin weakens the bacteria and makes it easier for the immune system or other antibiotics to effectively kill the bacteria. This helps in treating bacterial infections caused by susceptible bacteria.

Therefore, the correct answer is option 1, as penicillin blocks cell wall formation in bacteria.