Cell biology is the study of cells, their physiology, and how they work. It encompasses a wide range of topics from the structure and function of cell membranes to organelles, cell division, and cell death. Cell biologists use a variety of techniques to study cells, including microscopy, biochemistry, and genetics.
The field of cell biology emerged in the late 19th century when scientists began to realize that cells are the basic units of life. In 1839, German physician Matthias Jakob Schleiden proposed that all plants are made up of cells. Three years later, his compatriot Theodor Schwann extended this idea to animals. In 1855 Rudolf Virchow proposed that all living things arise from cells and that diseased tissues are simply collections of sick cells. These three men are therefore considered the fathers of modern cell biology.
Cells were first observed under the microscope in 1665 by Robert Hooke while he was studying cork through a compound microscope. He saw what looked like small compartments that he called “cells” because they reminded him of the small rooms monks lived in (cellula means “small room” in Latin). However, it was not until Anton van Leeuwenhoek improved upon the microscope design in 1674 that we began to see bacteria and other single-celled organisms in detail for the first time. Van Leeuwenhoek is therefore considered the father of microbiology.
It wasn’t until 1831 that Scottish botanist Robert Brown used a powerful new microscope to finally see plant cells clearly for what they were: tiny compartments separated by thin walls (the cell wall). This discovery led directly to Matthias Jakob Schleiden’s proposal that all plants are made up of cells just a few years later.
Theodor Schwann applied this same line reasoning to animals after observing animal tissue through a microscope in 1838 and concluding that it too was composed of individual cells separated by thin walls (the plasma membrane). Together these two men laid the foundation for modern cell theory which states that all living things are composed of one or more cells, that new cells arise from existing ones through cellular reproduction (or replication), and each cell contains hereditary information (DNA) which is passed on from generation to generation via these replicated daughter cells.