Who built his own microscope and observed microorganisms, calling them 'animalcules'?

• A. Leeuwenhoek
• B. Hooke
• C. Schleiden
• D. Virchow

Answer: (A)

Observing microorganisms and naming them animalcules was a milestone achieved by Antonie van Leeuwenhoek. He built his own simple, high-magnification lenses and used them in tiny single-lens microscopes to examine pond water, dental plaque, and other samples. From these observations, he described bacteria, protozoa, sperm cells, and more, referring to them as animalcules in his letters to the Royal Society. This hands-on, lens-by-lens approach laid the groundwork for microbiology and earned him the title often given to the pioneer of tiny-life discovery. The other figures contributed important ideas later on—Hooke described cells in cork and coined the term cell, while Schleiden and Virchow advanced cell theory—but they are not the ones who first built a microscope and observed microorganisms calling them animalcules.