Cell Theory Guided Notes

Cell Theory Guided Notes The cell theory is one of the key principles that underpins all of Biology. It is now universally accepted that all living organisms are made up of one or more cells, and that these are the most basic structure all living organisms. Today, cell theory has six core principles. 1. All living organisms are made up of cells. 2. The cell is the basic unit of life. 3. A new cell comes from a pre-existing cell. 4. All hereditary information is passed from a parent cell to a daughter cell during cellular reproduction. 5. All cells have similar chemical composition. 6. Energy flow occurs within cells. The Discovery of Cells The invention of the microscope was responsible for the eventual discovery of the cell and the formulation of the Cell Theory. The first breakthrough came from Robert Hooke in 1665 who made a compound microscope and used it to observe and draw pieces of cork. Hooke saw symmetrical borders in what appeared to be tiny holes in the cork he referred to these as cells. What Hooke actually saw without realizing were the empty cell walls of plant cells. He coined the name cell from the Latin word „cella‟ which is a small room where monks live. (Left) Robert Hooke's detailed drawing showing the cell walls of plant cells. (Right) Hooke's compound microscope. Cell Theory Guided Notes Later, Antonie van Leeuwenhoek (1638), after observing the same minute structures as Hooke, further explored cells and observed mobile objects. This discovery led him to believe that these were living organisms since movement is a characteristic of life. Leuwenhoek called these tiny creatures “animalcules,” which were actually bacteria and protozoa. Leuweenhoek also made many other discoveries such as identifying red blood cells and bacteria. He was also the first to observe fertilization and report that it required the sperm cell to enter the egg cell. This would be the key to disproving the theory of spontaneous generation. Leeuwenhoek’s detailed animalcule drawings. Approximately one hundred years later, Henri Dutrochet claimed that cell was the fundamental element of life. This also made it clear that the cell is also a physiological unit as well as a structural unit. In 1804, JHF Link and Karl Rudolphi further contributed to the nature of cells, proving that cells have independent cell walls. Cell Theory Guided Notes The History of Cell Theory The cell theory came about much later than the initial discovery of cells, having been first suggested by the German scientists Matthias Schleiden and Theodor Schwann in 1838 and 1839. Schleiden undertook miscroscopic research on plants and was the first to describe their cellular structure including the presence of the plant cell nucleus. Schwann built on Schleiden‟s work and in 1839 described the cellular structure of animal cells. Having previously studied a range of animal tissues including nerves, muscles and blood vessels, Schwann was able to observe and record the different properties of the cells in these structures. Left: Theodor Schwann Right: Matthias Schleiden Schwann eventually published his work on cells which drew three main conclusions regarding cell theory. These were: 1. The cell is the fundamental structure of life, 2. All organisms are made up of cells, and 3. Cells are formed through spontaneous generation. While the first two conclusion are true, are a part of the basic theory which underpins cell biology today, the concept of spontaneous generation was later disproved and rejected. Rudolph Virchow, after years of studying cell reproduction,eventually concluded that cells arise only from preexisting cells. With the evolution of modern molecular biology, the theory of cells has been expanded to cover concepts of heredity, cell energy production, and the study of the different structural components of cells. Cell Theory Guided Notes Cell Theory Timeline 1665 1670 1831 1838 1839 1840 1845 1855 • Robert Hooke observed tiny partitions when he viewed a piece of cork using his primitive compound microscope. He called these tiny partitions 'cells' and published his findings in his famous work, Micrographia. •Antonie van Leeuwenhoek saw tiny mobile objects in a drop of pond water with his microscope. •Leeuwenhoek made high quality lenses that could magnify objects more than 200x allowing him to view other mobile organisms such as bacteria and protozoa. •Robert Brown discovered the presence of a nucleus in plant cells. • Jakob Schleiden concluded that plant tissues are composed of cells and that the cell is the building block of plant matter. • Theodor Schwann concluded that animal tissues are made of animal cells. •Schwann published the first version of the cell theory. • Albrecht Von Roelliker discovered that the sperm and egg are also cells. • Carl Heinrich Braun defined the cell as the basic unit of life. • Rudolf Virchow hypothesized that cells must come from a pre-existing cell based on Brown's observation and Karl Nageli's study of cell division.