Penicillin, the first widely used antibiotic that revolutionised the treatment of bacterial infections, was discovered by which scientist?

Introduction / Context:
Penicillin is famous as the first widely used antibiotic drug, and its discovery marked a turning point in modern medicine. Before antibiotics, many bacterial infections that are now easily cured were often fatal. Recognising who discovered penicillin is a standard part of general science and biology knowledge and appears frequently in competitive exams and school tests.

Given Data / Assumptions:

• The substance in question is penicillin, an antibiotic derived from a mould.
• The discovery involved observing that a mould inhibited bacterial growth.
• The options include scientists known for vaccines, atomic models and electromagnetism.
• Only one of these names is directly tied to penicillin discovery.

Concept / Approach:
Sir Alexander Fleming, a Scottish bacteriologist, discovered penicillin in 1928 when he noticed that a mould contaminating one of his Petri dishes was killing nearby bacteria. The active substance from this mould became known as penicillin, and later researchers turned it into a practical drug. Edward Jenner is known for developing the smallpox vaccine, Niels Bohr for his atomic model and Heinrich Hertz for demonstrating electromagnetic waves. None of these scientists discovered penicillin, so Sir Alexander Fleming is the correct answer.

Step-by-Step Solution:
Step 1: Identify penicillin as an antibiotic drug produced by a mould.Step 2: Recall that Alexander Fleming discovered its antibacterial effect by chance in a laboratory.Step 3: Look at the options and find Sir Alexander Fleming listed as option C.Step 4: Recognise that Edward Jenner work relates to vaccination against smallpox, not antibiotics.Step 5: Recognise that Niels Bohr contributions are in atomic physics and that Heinrich Hertz contributions relate to electromagnetic waves.Step 6: Select Sir Alexander Fleming as the discoverer of penicillin.

Verification / Alternative check:
Biology textbooks and medical history references consistently repeat the story of Fleming Petri dish and the mould Penicillium notatum inhibiting bacterial growth. They describe how his observation led to the development of penicillin as a drug. Jenner, Bohr and Hertz names appear in entirely different chapters on vaccination, atomic theory and electromagnetic waves. Because the association between penicillin and Fleming is so strong, he is the only correct choice in this multiple choice question.

Why Other Options Are Wrong:
Edward Jenner pioneered vaccination by using material from cowpox lesions to protect against smallpox. Niels Bohr proposed the Bohr model of the atom and contributed to quantum theory. Heinrich Hertz verified the existence of electromagnetic waves predicted by Maxwell equations. These achievements are significant but unrelated to antibiotic discovery. Therefore, options A, B and D are incorrect answers to a question about penicillin discovery.

Common Pitfalls:
Candidates sometimes confuse vaccine and antibiotic discoveries because both relate to fighting disease. Others may recognise the name Jenner and pick it without paying attention to whether the substance mentioned is a vaccine or a drug. To avoid such confusion, remember simple mappings: Jenner and smallpox vaccine, Fleming and penicillin, Salk and polio vaccine. This way, you can quickly distinguish between different medical breakthroughs in MCQs.

Final Answer:
Penicillin was discovered by Sir Alexander Fleming.