Name the instrument (or device) which is needed to see the microorganisms.

A microscope is the essential instrument required to observe microorganisms, as most are far too small to be seen with the naked eye. The compound light microscope, most commonly used in schools and basic laboratories, uses visible light and multiple glass lenses to magnify specimens between 40 to 1000 times their actual size, making bacteria, protozoa, fungi, and algae visible. More advanced microscopes like electron microscopes can magnify objects up to millions of times, revealing even viruses and intricate cellular details.

The invention and refinement of the microscope revolutionized biology by opening the invisible microbial world to scientific study. Dutch scientist Antonie van Leeuwenhoek is credited with developing early microscopes in the 1670s that first revealed bacteria and protozoa, which he called "animalcules." Today, microscopy remains fundamental in medical diagnosis, research, quality control in industries, and education, enabling us to identify pathogens, study cell structures, and understand the vast diversity of microscopic life.