Which Dutch merchant made the first simple microscope with magnification around 300x to examine cloth quality, later reporting protozoa in 1674 and bacteria a few years later?

• A. Antoni van Leeuwenhoek
• B. Robert Hooke
• C. Louis Pasteur
• D. Ferdinand Cohn

Answer: (A)

Antoni van Leeuwenhoek is the figure described. He was a Dutch cloth merchant who ground and polished tiny single-lens microscopes capable of about 200–300x magnification. He used these lenses to inspect fabrics, but their power revealed living microorganisms for the first time. In 1674 he reported observing tiny moving organisms in a drop of water—protozoa—calling them animalcules. A few years after that, he described bacteria as well, making him the first to document both groups of microorganisms. This combination of profession, instrument type, magnification, and the timing of protozoa then bacteria observations matches him uniquely. Other scientists mentioned—Hooke, Pasteur, Cohn—fit different eras, instrument approaches, or discoveries.