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 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
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.
1858
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/picturegalleries/7924099/Creepy-crawlies-Amazing-ScanningElectron-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