History of Cell Theory and Modern Cell Theory The Cell Overview History of Cell Theory and Modern Cell Theory

History of Cell Theory Development Robert Hooke - The first person to see cells, he was looking at cork and noted that he saw "a great many boxes. (1665) Anton van Leeuwenhock - Observed living cells in pond water, which he called "animalcules" (1673) Theodore Schwann - zoologist who observed that the tissues of animals had cells (1839) Mattias Schleiden - botanist, observed that the tissues of plants contained cells ( 1845) Rudolf Virchow - also reported that every living thing is made of up vital units, known as cells. He also predicted that cells come from other cells. (1850 )

The modern tenets of the Cell Theory include: all known living things are made up of cells. the cell is structural & functional unit of all living things. all cells come from pre-existing cells by division.          (Spontaneous Generation does not occur).   cells contains hereditary information which is passed from cell to cell during cell division. All cells are basically the same in chemical composition. all energy flow (metabolism & biochemistry) of life occurs within cells  .    

Theory! Not Law   As with any theory, its tenets are based upon previous observations and facts, which are synthesized into a coherent whole via the scientific method. The Cell Theory is no different being founded upon the observations of many. 

Exceptions to the Cell Theory 1. Viruses - are they alive ? According to the Cell Theory we have to say "no" because a virus is not a cell.  Viruses are made of two chemicals, protein & nucleic acid, but have no membranes, nucleus, or protoplasm. They appear to be alive when they reproduce after infecting a host cell. 2. Mitochondria & chloroplasts. These cell organelles (small structures inside the cell) have their own genetic material & reproduce independently from the rest of the cell.

Another exception 3. Where did the first cell come from ? According to statement #3 of the cell theory, all cells come from other living cells.  So how did the first cell ever appear ?  It's the old "chicken & egg" dilemma.  We will investigate this question (& its possible answer) in more detail during the Evolution Unit.

Tools of the Biologist 1.)Ultracentrifuge Separates things by density. Commonly used to separate cell organelles/ blood components

Tools of the Biologist 2.) Microdissection instrument Used to separate microscopic components (cell parts, bacteria)

Tools of the Biologist 3.) Cell Cultures A cell is able to reproduce into a group of cells. A cell is placed in a nutrient solution so it can reproduce. Ex: Strep Throat cultures

Tools of the Biologist 4.) Compound Light Microscope Light passes through a specimen & 2 lenses to form an image. Produces magnifications about 100 - 1,000 X. Specimens may be live or dead.

Tools of the Biologist 5.) Stereo/dissecting Microscope Produces 3-D images of living or dissected specimens. Used with larger objects where light cannot pass through

Tools of the Biologist 6.) Electron Microscope Focus beams of electrons on specimens 1000x smaller than can be viewed with Light microscope

Tools of the Biologist A.) Transmission electron microscope Produces slices of specimens

Tools of the Biologist B.) Scanning Electron Microscope Produces incredible 3-D images of entire specimen.

NANOWORLD IMAGES electron microscope image of a fruit fly's compound.