Cell Discovery & Cell Theory

It all started with an invention. The first microscope Zacharias Jansen, 1595, Middleburg, Holland It launched great leaps in Astronomy and Biology. Some of the first great observations with it were made by

Robert Hooke (1635-1703) Designed microscopes Discovered and documented the first cells in 1665 Named them after the cells in which a monk sleeps.

Robert Hooke (1635-1703) Released book of detailed drawings and observations: Micrographia, 1665 Drawing of Flea Hooke had a life-long rivalry with Sir Isaac Newton. Newton worked hard to destroy his reputation during and after his death. Much of Hooke s work was destroyed even his gravesite is still unknown.

Images from Micrographia

Antony van Leeuwenhoek (1632-1723) A tradesman from Holland who became fascinated with Hooke s book Discovered bacteria, protists, sperm cells, blood cells, nematodes, etc. Became an expert lens grinder and made over 500 simple microscopes Acute eyesight and lens grinding skill let him build microscopes that were capable of 200X magnification

Cell Theory 1838 Mattias Schleiden stated that all plant tissues consisted of cells 1839 Theodore Schwann stated that all animal tissues consisted of cells Each conjectured that there was a nucleus 1858 Rudolf Virchow combined the two ideas and added that all cells come from pre-existing cells, formulating the Cell Theory

Rudolf Virchow 1858 Cell Theory All living things are composed of one or more cells In organisms, cells are the basic units of structure and function. All cells are produced only from existing cells.

What is a Theory?

Definition Common Cultural Definition: A hypothesis proposed as an explanation; hence, a mere speculation as an individual viewpoint. Example: I have a theory that the Skyline Football Team will win state because of the number of seniors on the team. Problem: There is very limited if no evidence to back this statement up. It is more of a hypothesis.

Definition Scientific Definition: An explanation for facts or phenomena that has been confirmed or established by observation or experiments of many types and over many years. It is accepted as accounting for the known facts. With new technology and increasing knowledge, some theories get stronger. Examples: The Cell Theory The Theory of Evolution

Just a Theory? It means that it is the BEST explanation we have for why something happens. Putting just in front of a theory diminishes the true value of a scientific theory.

Theory vs Law Scientific Laws describe WHAT is happening. Examples include: Newton s Laws of Gravity, Kepler s Laws of Planetary Motion, Law of Conservation of Energy, Laws of Thermodynamics. Scientific Theories explain WHY something happens. Examples include: The Big Bang Theory, Cell Theory, Theory of Relativity, Theory of Evolution

Modern Microscopes Some of the light microscopes here are capable of 1000x magnification. That is about the limit of a light microscope s magnification without losing clarity (called Resolving Power). Due to the width of visible light s wavelength The electron microscope was introduced in the 1950s and uses the wavelength of electrons to increase the resolving power by 100x. Approx. 100,000x magnification!! Cell Biology advanced rapidly as cellular organelles were clearly seen for the first time.

Resolving Power

Modern Microscopes Transmission Electron Microscope (TEM) magnifies a slice of a sample. (Rabbit trachea cilia) Scanning Electron Microscope (SEM) shows 3D image of the Rabbit trachea cilia

A few limitations of electron microscopes Specimen must be placed in a vacuum and is typically coated with a conductive metal like gold. Consequently you can t look at living specimens under electron microscopes. All images produced are black and white, so you can t distinguish colors. Pictures are usually colored in digitally later.

Other Cool SEM pictures http://www.telegraph.co.uk/science/picture- galleries/7924099/creepy-crawlies-amazing-scanning- Electron-Microscope-pictures-of-insects-and-spiders.html

Carbon atoms bonded to hydrogen

Fruit fly with four eyes under an SEM

Vocabulary: Cell History Jansen Hooke Van Leeuwenhoek Schleiden Schwann Virchow Cell Theory Resolving Power Light Microscope Electron Microscope