Which early microscopist is credited with discovering bacteria by observing tiny living cells through his handcrafted lenses?

Introduction / Context:
Bacteria are microscopic single celled organisms that play major roles in health, disease and the environment. The discovery of bacteria required powerful lenses and careful observation. This question asks which early microscopist is credited with first observing and describing bacteria using simple handcrafted microscopes.

Given Data / Assumptions:

• The focus is on the first discovery of bacteria, not later classification or disease links.
• The discovery involved direct observation through lenses.
• The options list several scientists from the history of biology and microbiology.
• We assume familiarity with basic names in the development of microbiology.

Concept / Approach:
Antonie van Leeuwenhoek, a Dutch tradesman and self taught scientist, made very fine single lens microscopes. In the seventeenth century he examined samples of pond water, plaque and other materials and described tiny living organisms, which included bacteria and protozoa. He sent detailed letters about these observations to the Royal Society, earning him recognition as the discoverer of bacteria and other microscopic life forms.

Step-by-Step Solution:
Step 1: Recall that Leeuwenhoek is often called the father of microbiology. Step 2: Recognise that he used powerful single lens microscopes to see what he called animalcules, many of which were bacteria. Step 3: Distinguish his role from Robert Koch and Louis Pasteur, who came later and studied specific bacterial diseases and vaccination. Step 4: Conclude that Antonie van Leeuwenhoek is the correct answer.

Verification / Alternative check:
Almost every microbiology textbook begins its historical overview by mentioning Leeuwenhoek observations of bacteria and protozoa. The names Koch and Pasteur appear later in connection with germ theory and specific pathogens. Because the question asks who discovered bacteria, not who proved the germ theory of disease, Leeuwenhoek stands out as the right choice.

Why Other Options Are Wrong:

• Robert Brown: Known for discovering the cell nucleus and describing Brownian motion, not for discovering bacteria.
• Robert Hooke: Coined the term cell when looking at cork, but did not first observe bacteria.
• Robert Koch: Demonstrated that specific bacteria cause specific diseases but lived long after bacteria were first seen.
• Louis Pasteur: Worked on fermentation and vaccination, and supported the germ theory, but did not make the first discovery of bacteria.

Common Pitfalls:
Learners sometimes choose Koch or Pasteur because they strongly associate these names with bacteria and disease. However, the question is specifically about first discovery under the microscope, which clearly belongs to Leeuwenhoek. Keeping the timeline in mind helps: Leeuwenhoek observed bacteria first, and later scientists built on his work to develop modern microbiology and medicine.

Final Answer:
Antonie van Leeuwenhoek is credited with discovering bacteria by observing them through his handcrafted microscopes.