Final answer:
Antonie van Leeuwenhoek was the first scientist to see and describe microorganisms viewed under a microscope.
Step-by-step explanation:
The scientist who was the first to see and describe microorganisms viewed under a microscope was Antonie van Leeuwenhoek. Born in the city of Delft in the Dutch Republic, van Leeuwenhoek created powerful microscopes that allowed him to observe microorganisms like bacteria and protists. In 1674, he described his observations of single-celled organisms in a series of letters to the Royal Society of London. Van Leeuwenhoek's findings were initially met with skepticism, but they were later verified, solidifying his place in the history of microbiology.