Understanding Cell Biology: History & Theories

Instructor: Meredith Mikell
The study of cells is one of the fields most crucial to understanding biology, even though it is a relatively new field. Here we will go through a brief history of cell biology and examine its key theories.

All Life Are Cells

All living things are made up of cells. They are the smallest unit of life. Some organisms are comprised of one cell while others are a conglomeration of many cells. Understanding cell function constantly reveals dynamic and even mystifying intricacies. Because individual cells are usually too small to see with the naked eye, the field of cell biology did not exist until the 17th century.

A First Look At Cells

We got our first look at cells when English physicist Robert Hooke made his first observations of cork cells in 1665. Microscopes had been around for about sixty years at that point, but their use wasn't directed at biological functions. Hooke took note of tiny compartments within cell walls that he described as analogous to the many rooms within a monastery. Some of Hooke's contemporaries began to identify smaller structures within plant cells, now known as organelles.

One of Hooke
microscope

During these first observations, scientists did not understand or suggest that cells make up the basic unit of all living things, or that individual cells could be individual organisms. In the 1670s, a Dutch biologist named Antonie van Leeuwenhoek observed single-celled organisms, including protists, bacteria, and human sperm. He also made significant contributions to the study of microbiology by improving the strength of microscope lenses.

Early drawings of observed cells.
early cells

Cell Theory

It took another hundred years after those first cell observations for the ubiquitous nature of cells to be fully recognized. The concept of Cell Theory holds that:

- All living things are made up of at least one cell

- The cell is the most fundamental unit of life

- Cells can only arise from existing cells

In the 1820s, French biologist Henri Milne-Edwards concluded that animal tissue could be reduced down to individual globules, but insisted that they all have the same size and shape, which was later proven otherwise. Not long after, another French scientist Francoise Raspail established one of the concepts of cell theory: that all cells arise from exiting cells. This concept was built-upon in the 1830s by Barthelemy Dumortier who witnessed binary fission under the microscope, in which a single-cell splits into two daughter cells. German biologists Matthias Schleiden and Theodor Schwann looked more closely at plant and animal cells, eventually establishing that individual cells are THE unit that comprise ALL plant and animal tissue. They are credited as the founders of Cell Theory, though as you can see, many biologists made gradual contributions to this widely-accepted concept.

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