Penicillin's Source and Use Steps:

• Identify penicillin's producer: It's derived from the mold Penicillium, a fungus.
• Recall penicillin's function: As an antibiotic, it targets bacterial cell walls to kill or inhibit bacteria.
• Match to choices: Producer is fungus; treats bacterial infections.
• Eliminate mismatches: Options with bacterium or viral don't fit.

Why D is correct:

• Penicillin is produced by the fungus Penicillium chrysogenum and treats bacterial infections by disrupting peptidoglycan synthesis in bacterial cell walls.

Why the others are wrong:

• A: Penicillin is not produced by bacteria.
• B: Penicillin is not produced by bacteria and does not treat viral infections.
• C: Penicillin treats bacterial, not viral, infections.

Final answer: D