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A prokaryote, a simple cell

Cell theory is a scientific theory that is one of the foundations of biology.

The generally accepted parts of cell theory include:

• The cell is the fundamental unit of structure and function in living things.
• All organisms are made up of one or more cells.
• All cells come from pre-existing cells through cellular division.
• Cells carry genetic material passed to daughter cells during cellular division.
• All cells are essentially the same in chemical composition.
• Energy flow (metabolism and biochemistry) occurs within cells.

This theory also contains two exceptions:

1. Viruses are considered by some to be alive, yet they are not made up of cells.
2. The first cell did not originate from a preexisting cell.

The cell was first discovered and named by Robert Hooke in 1665. He remarked that it looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the dead cell walls of plant cells also known as cork^{[citation needed]}. These cell walls lacked the nucleus and other organelles found in most living cells. The first man to witness a live cell under a microscope was Anton van Leeuwenhoek, who in 1674 described the algae Spirogyra^{[citation needed]}. van Leeuwenhoek also described bacteria which he referred to as animalcules^{[citation needed]}.

Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word "cell".

The first scientist to recognize the commonality of structure in making up both plants and animals was Charles-François Brisseau de Mirbel who in 1809 stated that

The naturalist Jean-Baptiste Lamarck also recognized that living things were made of cells, extending the idea beyond plants to all living organisms saying

Both Mirbel and Lamarck saw living things as being made of cells but did not see cells as a distinct primary part of living structures but rather thought of cells as the mebranes surrounding the spaces rather than the spaces themselves.^[3]. The idea of cells were separable into individual units was proposed by Ludolph Christian Treviranus^[4] and Johann Jacob Paul Moldenhawer^[5]. All of this finally led to Henri Dutrochet formulating one of the fundamental tenets of modern cell theory by declaring that

Credit for developing Cell Theory is usually given to two scientists, Theodor Schwann, a zoologist and Matthias Jakob Schleiden, a botanist. In 1839 these two scientists suggested that cells were the basic unit of life. Their theory accepted the first two tenets of modern cell theory. However the cell theory of Schleiden differered from modern cell theory in that it proposed a method of spontaneous crystallization that he called "Free Cell Formation"^[7].

• http://fig.cox.miami.edu/~cmallery/150/unity/cell.text.htm
• http://www.biology.arizona.edu/cell_bio/tutorials/cells/cells3.html
• http://www.edu.pe.ca/vrcs/2003/courses/9science/timeline.htm
• http://www2.bc.edu/~strother/GE_146/lectures/12.html
• http://www.cellsalive.com