Transcript Decent With Modification Darwin’s Theory

Psalm 119:99,100
99 I have more understanding
than all my teachers: for thy
testimonies are my
meditation.
100 I understand more than the
ancients, because I keep thy
precepts.
©2001 Timothy G. Standish
Electron
Microscopy
Timothy G. Standish, Ph. D.
©2001 Timothy G. Standish
History and Applications
Electron microscopes were developed around the
same time as the development of television sets and
utilize much of the same technology
 They take advantage of the short wavelength of
electrons. As the wavelength is shorter, higher
resolution is possible than with regular light
microscopes
 Scanning Electron Microscopes (SEM) are
analogous to dissecting microscopes
 Transmission Electron Microscopes (TEM) are
similar in principle to compound microscopes

©2001 Timothy G. Standish
A Television Monitor
Electron beam
Magnets
-Electron Gun
Vacuum
+
Phosphore coated screen
©2001 Timothy G. Standish
Scanning Electron Microscopy
 SEM
is very good for looking at surfaces
 SEM gives almost infinite depth of field
 SEM cannot show color
 With the right detectors SEM can be used to
determine the elements in a sample
 SEM can go to high magnifications, but
cannot achieve magnifications as high as
those achieved with Transmission Electron
Microscopy
©2001 Timothy G. Standish
Scanning Electron Microscope
+
…..
©2001 Timothy G. Standish
Scanning Electron Microscope
Filament
+
Magnet
“lenses”
Beam
deflector
Electrons
Focused
Electron beam
Sample
Stub
©2001 Timothy G. Standish
Scanning Electron Microscope
Filament
-
Magnet
“lenses”
Beam
deflector
Electrons
Focused
Electron beam
Electron
detector
+
Sample
…..
Stub
Reflected electrons
©2001 Timothy G. Standish
Scanning Electron Micrographs
May Fly
Head
Bee Eye
©2001 Timothy G. Standish
More S. E. Micrographs
Leaf With Bacteria
Burr
Anther
©2001 Timothy G. Standish
Transmission Electron
Microscopy
TEM allows for very high magnification due to the
short wavelength of electrons
 TEM is very good for looking inside cells, but is
not very good for studying surfaces
 Preparation of samples for TEM is time consuming
and difficult
 No natural color is possible with transmission
electron micrographs

©2001 Timothy G. Standish
Transmission Electron Microscope
Filament
-
Magnet
“lenses”
Focused
Electron beam
Beam
spreader
Ultra vacuum
Electrons
Sample
To a very
efficient pump
+
Window
Phosphore coated target
©2001 Timothy G. Standish
Transmission Electron Micrograph
Diaphragm 24,000 X
©2001 Timothy G. Standish
Transmission Electron Micrograph
Sperm Tail XS, 28,000 X
©2001 Timothy G. Standish
©2001 Timothy G. Standish