Transcript Planet Earth and Its Environment A 5000-million year

Patterns in Nature
Topic 3: Technological Advances and the Development of the
Cell Theory
Part of the Patterns in Nature Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
Dot Point
 Discuss the significance of the technological advances of
the cell theory
blogs.discovermagazine.com
Continued Advances in Light Microscope
Technology
Improvements to the light
microscope continued and in
the 1870’s, oil immersion
lenses were introduced by Zeiss
and Abbe, enabling a good
image up to 1500x
magnification to be seen.
optimaxonline.com
Continued Advances in Light Microscope
Technology
BY the 1980’s the top level microscopes of the time were fairly
similar in their viewing capacity to the current senior school
microscopes.
100x
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Over the next 100 years improvement of images produced by microscopes
has resulted from ongoing research into the technology
The Invention of the electron microscope
By the end of the 19th century compound microscopes had been
developed to a point where they were no longer limited by the
quality of the lens.
Cell Mitosis, Onion
root 1200x
fphoto.photoshelter.com
Their main limiting factor had become wavelength of light.
The Invention of the electron microscope
The wavelength of visible light (0.5m) limits the resolving power
of microscopes so that objects closer together than 0.45m are no
longer seen as separate objects.
quia.com
The Invention of the electron microscope
The best optical
microscopes cannot
effectively magnify larger
than 2000x. As a result,
scientists began
experimenting with other
forms of energy than light.
microscope-microscope.org
The Invention of the electron microscope
In 1933, the invention of the
transmission electron microscope
was the next great breakthrough in our
knowledge of cells. Images are produced
using a beam of electrons that could
magnify up to 12000x.
en.wikipedia.org
Ernst Ruska and Max Kroll continued working on the electron microscope
during the second world war and created an instrument that had a
magnification of 1000000x!
The Invention of the electron microscope
The basic principle of
the transmission
electron microscope
(TEM) is similar to that
of a compound
microscope, except that
the energy source
transmitted through the
specimen is a beam of
electrons instead of a
beam of light.
ccber.ucsb.edu
The Invention of the electron microscope
The electrons must pass through a vacuum (otherwise the image is
distorted) so only non-living specimens can be viewed. The
electrons are focused using electron magnets and the image is
produced on a screen where it shows up as fluorescence.
bio.mq.edu.au
The Invention of the electron microscope
The invention of the scanning electron microscopes followed
in 1955. The electron beam in this instrument causes the
specimen to emit its own electrons. This produces a three
dimensional image.
publications.nigms.nih.gov
Advantages of electron microscope
The main advantage of the TEM is the high magnification (ability to
enlarge an image) and resolution (ability to distinguish two very close
objects as separate images).
Individual Layers of a Cell
Membrane
wikispaces.psu.edu
TEM can reveal structures at a sub-cellular level. This has enabled
scientists to see organelles for the first time which has led to a better
understanding of their functions.
Disadvantages of electron microscope
The main disadvantage of
TEM’s is that living tissue
cannot be viewed. Also the
size, expense and
maintenance makes them
unavailable to the general
public and schools.
jeol.com
Techniques for preparing specimens for viewing
The preparation of tissue for viewing under microscopes has
become an integral part of microscopy. As microscopes have
evolved so has the methods and technology for preparing
specimens.
biosci.ohio-state.edu
Techniques for preparing specimens for viewing
Two main criteria must be met when preparing tissue for viewing
under the microscope:
1. The sections must be thin enough to allow light or electrons
to pass through them
2. Very thin sections of living tissue are mostly transparent, so
the structure is difficult to observe unless some contrast is
created (needed) between tissue and its background. Staining is
used to create this contrast.
healthmatters2day.blogspot.com
Techniques for preparing specimens for viewing
While preparing the tissue for viewing, the technique should
minimise the alteration of tissue from it’s living form, otherwise
what we view may be an artefact (artificial structure). To meet the
preparation criteria a four step process is used to prepare slides:
1. Fixation
2. Embedding
3. Slicing or sectioning
4. Staining
healthmatters2day.blogspot.com
Techniques for preparing specimens for viewing
Fixation
 The tissue is placed into a preservative substance that kills and
preserves the cells as closely to the living tissue as possible.
pathology.utscavma.org
Techniques for preparing specimens for viewing
Embedding
 Tissue is embedded into a hard medium (a wax or resin) to
overcome the difficulty of cutting the soft tissue into thin slices
leica-microsystems.com
Techniques for preparing specimens for viewing
Slicing or Sectioning
 A machine called a microtome (today we have ultramicrotromes) has
been invented to cut the specimens into ultra thin slices.
Thinner sections allows greater clarity the image.
nl.wikipedia.org
Techniques for preparing specimens for viewing
Staining:
 Colour is produced by a variety of stains to create a contrast
between the transparent material and its background. Heavy
metals may be used to stain tissue for viewing under the
electron microscope.
mycology.adelaide.edu.au
The electron microscope and further
developments in the cell theory
The development of the electron microscope has allowed scientists
to study the ultrastructure of cells. They are now also linked to
computers which has enabled the study of sub-cellular structures
in great detail providing evidence of their structure and function.
microscope.maggie168888.com
The electron microscope and further
developments in the cell theory
This technology is also used in the areas of genetics and ecology,
providing evidence which has resulted in modern biologists adding
a further three statements to the cell theory:
4. Cells contain hereditary information which is passed on during
cell division
5. All cells have the same basic chemical composition
6. All energy flow (resulting from chemical reactions) of life
occurs within cells.
healthmatters2day.blogspot.com
Further advances in microscopy
 Current developments in compound microscopes where the
image is linked up with computers has allowed the image to be
digitally enhanced.
 Confocal microscopes use laser light to allow a three
dimensional view of a specimen to be build up.
 Synchrotrons accelerate electrons and can be used to study
structure at an atomic level.
healthmatters2day.blogspot.com
Homework
Answer the following questions in your notebook. Be prepared
to discuss next lesson.
 Identify two technological advancements which led to the
advancement in the cell theory. Use an example for each
advancement
 Hand out Student Activity: Creating a table to compare light and
transmission microscopes.