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

Images from Micrographia

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 Theory1838 Mattias Schleiden stated that

all plant tissues consisted of cells1839 Theodore Schwann stated that

all animal tissues consisted of cellsEach conjectured that there was a

nucleus1858 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.

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

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

Modern Microscopes

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 HistoryJansen Light MicroscopeHooke Electron MicroscopeVan LeeuwenhoekSchleiden SchwannVirchowCell TheoryResolving Power