How he discovered them:

* Microscopes: Leeuwenhoek was a skilled lens grinder and crafted powerful microscopes that could magnify objects hundreds of times.

* Pond Water Observation: He observed pond water samples under his microscope and noticed tiny, moving particles.

* Detailed Observations: He meticulously documented his observations, drawing detailed sketches of the tiny creatures he saw, which he referred to as "animalcules."

Significance of his discovery:

Leeuwenhoek's discovery of living cells in pond water was groundbreaking because it revealed the existence of a microscopic world previously unknown to humans. His observations laid the foundation for the study of microbiology and helped establish the cell theory, which states that all living organisms are made up of cells.