1. Robert Hooke: In 1665, Hooke observed thin slices of cork under a microscope and described the small, box-like compartments he saw as "cells." While he didn't realize these were living units, his work was the first to describe the cellular structure of organisms.
2. Anton van Leeuwenhoek: In the late 1600s, Leeuwenhoek, using his own improved microscopes, observed and described various single-celled organisms, including bacteria, which he called "animalcules." His discoveries showed the existence of microscopic life, further supporting the idea of cells as basic units of life.
3. Theodor Schwann and Matthias Schleiden: In the 1830s, Schwann studied animal tissues and Schleiden studied plant tissues. Both independently observed that all living organisms were composed of cells. Their work, along with the contributions of others, led to the formulation of the Cell Theory, which states that all living organisms are composed of cells and that all cells arise from pre-existing cells.
