Who was first to discover evidence of microorganisms?

• A. Louis Pasteur
• B. Anton van Leeuwenhoek
• C. Robert Koch
• D. Alexander Fleming

Answer: (C)

The earliest evidence that microorganisms exist comes from Anton van Leeuwenhoek. In the 1670s he built highly magnifying single-lens microscopes and carefully examined samples such as pond water and dental plaque. From these observations he described tiny, living creatures—bacteria, protozoa, and other micro-organisms—reporting them in letters and drawings. This was the first documented proof that life exists at a microscopic scale, long before scientists connected microbes to disease or developed antibiotics. Later on, researchers like Pasteur, Koch, and Fleming expanded on this foundation in different ways, but van Leeuwenhoek is the one who first revealed that unseen life forms inhabited the world.