Cell theory, a basic principle of biology, includes three key ideas. According to cell theory, all living things are made up of cells. A cell is the basic unit of function and structure in all organisms, and all cells come from previous cells. These ideas result from the contributions of many different scientists.
Van Leeuwenhoek Invents the Microscope
The contributions of later scientists to cell theory depended on the existence of the microscope. Although compound microscopes already existed, the Dutch lensmaker Anton van Leeuwenhoek developed a much more powerful microscope in the 1600s. Compound microscopes could magnify an object about 30 times; van Leeuwenhoek's microscope provided magnifications up to 200 times. Using his microscope, van Leeuwenhoek was able to discover that individual droplets of water contained many tiny living beings. This discovery paved the way for later scientists to examine the world around them using a more powerful microscope, which led to the development of cell theory.
Robert Hooke Discovers Cells
Using the more powerful microscope invented by van Leeuwenhoek, Robert Hooke examined slices of wood, cork and plant stems. He observed that these plant materials were made up of thousands of tiny divisions or chambers. Hooke called each chamber a "cell" because they called to mind the tiny rooms that housed individual monks in the monasteries of his day. Hooke published his findings about cells in a work called "Micrographia" in 1665.
Contributions to Cell Theory in the 1800s
Cell theory continued to develop during the 1800s. Scottish scientist Robert Brown noticed in 1833 that all cells had a dark area in the approximate centre. This dark area is now called the nucleus. Five years later, the German botanist Matthias Schleiden put forth the theory that all plants are composed of cells. In 1839, the German scientist Theodor Schwann stated that animals are also composed of cells. By 1855, cell theory was complete when German physician Rudolf Virchow discovered that all cells result from the division of previously existing cells.
Contributions to Cell Theory in the 1900s
Even though basic cell theory was complete by 1855, scientists continued to study the structure and function of cells to gain new understanding of the basic building blocks of life. In 1931, Janet Plowe proved that the cell membrane is more than just an exchange of liquids between cells; it is a separate physical structure with characteristics of its own. One of the most recent significant discoveries happened in 1970 when Lynn Margoulis theorised that some organelles inside cells used to be independent organisms.
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