User:Jvbishop/celltheorydraft

A prokaryote, a simple cell

Cell theory is a scientific theory that is one of the foundations of modern biology. Cell theory is considered the first of the great paradigms of biology, later joined by the theories of Evolution and Heredity. Cell theory was developed gradually through the later parts of the 18th century and the beginning of the 19th century. Credit for the formualation that of cell theory is often given to a Theodor Schwann, and Matthias Jakob Schleiden, however all parts of the theory had been discovered by previous scientists. In its simplest form, Cell theory can be summarized as saying that:

 1. All living organisms are composed of one or more cells.
 2. Cells are the most basic unit for function and structure of all organisms.
 3. All cells come from cells that already exist.
 4. The life of any organism depends on the combined effort of all its cells.

Modern Cell Theory

Cell theory deals with the nature of the cell and its role and importance in life. Cell theory as currently accepted can be broken into several different postulates and two exemptions.

Postulates

The cell is the fundamental unit of structure and function in living things.

This postulate states that the cell is a contained independent structure. Every cell had its own independent existence, i.e. carried out its own respiration, metabolism, etc., and, most importantly, had the ability to reproduce. This was the idea two German biologists called Matthias Schleiden and Theodor Schwann who proposed the idea in 1838.

All organisms are made up of one or more cells.

Definition of orgasnism

All cells come from pre-existing cells through cellular division. Cells recieve genetic material from their progenitor cells.

All cells have as their origin a biologic creation through cellular division. All cells carry hereditary information in the form of DNA and RNA which can be transmitted to the daughter cells.

All cells are essentially the same in chemical composition. Energy flow (metabolism and biochemistry) occurs within cells.

This postulates that all cells are made of the same basic building blocks of life. The main building block is the protein, a complex organic molecule, made of several amino acids. Virtually all cellular machinery is made of proteins. Other main chemical components of cells include carbohydrates, lipids, and

Exceptions

Viruses are considered by some to be alive, yet they are not made up of cells

The view that viruses are alive is a conscientious one and not held by the majority of virologists. For those that do hold that viruses are alive they view viruses as an exemption to the accepted version of cell theory.

The first cell did not originate from a preexisting cell

This referers to a theory known as abiogenesis.

History of Cell Theory

Scientific theories are generally the result of many observations made be many scientists. Cell theory is no different. Credit for a theory is often given to the first researcher who postulates the theory in such a way so as to gain wide acceptance for the theory among scientists. Many discoveries went into the forming of cell theory but it was not until the Release of Theodor Schwann's {book name}.

The cell was first discovered and named by Robert Hooke in 1663. 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. 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. van Leeuwenhoek also described bacteria which he referred to as animalcules.

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

“ Plants are made up of cells, all parts of which are in continuity and form one and the same membranous tissue ”

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

“ Thus every living body is essentially a mass of cellular tissue ”

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 membranes surrounding the spaces rather than the spaces themselves.. The idea of cells were separable into individual units was proposed by Ludolph Christian Treviranus and Johann Jacob Paul Moldenhawer. All of this finally led to Henri Dutrochet formulating one of the fundamental tenets of modern cell theory by declaring that

“ The cell is the fundamental element of organization ”

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 suggestesd 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".

Rudolph Virchow

External links

• 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