Planet Earth and Its Environment A 5000-million year Journey

Part of the Patterns in Nature ModuleBiology in Focus, Preliminary CourseGlenda Childrawi and Stephanie HollisPatterns in NatureTopic 3: Technological Advances and the Development of the Cell TheoryDot PointDiscuss the significance of the technological advances of the cell theory

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Continued Advances in Light Microscope TechnologyImprovements to the light microscope continued and in the 1870s, oil immersion lenses were introduced by Zeiss and Abbe, enabling a good image up to 1500x magnification to be seen.

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Continued Advances in Light Microscope TechnologyBY the 1980s the top level microscopes of the time were fairly similar in their viewing capacity to the current senior school microscopes.

Over the next 100 years improvement of images produced by microscopes has resulted from ongoing research into the technology

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100xThe Invention of the electron microscopeBy 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.

Their main limiting factor had become wavelength of light.

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Cell Mitosis, Onion root 1200xThe Invention of the electron microscopeThe wavelength of visible light (0.5m) limits the resolving power of microscopes so that objects closer together than 0.45m are no longer seen as separate objects.

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The Invention of the electron microscopeThe best optical microscopes cannot effectively magnify larger than 2000x. As a result, scientists began experimenting with other forms of energy than light.

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The Invention of the electron microscopeIn 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.

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!

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The Invention of the electron microscopeThe 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.

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The Invention of the electron microscopeThe 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.

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The Invention of the electron microscopeThe 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.

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Advantages of electron microscopeThe 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).

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.

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Individual Layers of a Cell MembraneDisadvantages of electron microscopeThe main disadvantage of TEMs is that living tissue cannot be viewed. Also the size, expense and maintenance makes them unavailable to the general public and schools.

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Techniques for preparing specimens for viewingThe 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.

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Techniques for preparing specimens for viewingTwo main criteria must be met when preparing tissue for viewing under the microscope:The sections must be thin enough to allow light or electrons to pass through themVery 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.comTechniques for preparing specimens for viewingWhile preparing the tissue for viewing, the technique should minimise the alteration of tissue from its 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:FixationEmbeddingSlicing or sectioningStaining

healthmatters2day.blogspot.comTechniques for preparing specimens for viewingFixationThe tissue is placed into a preservative substance that kills and preserves the cells as closely to the living tissue as possible.

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Techniques for preparing specimens for viewingEmbeddingTissue is embedded into a hard medium (a wax or resin) to overcome the difficulty of cutting the soft tissue into thin slices

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Techniques for preparing specimens for viewingSlicing or SectioningA 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.

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Techniques for preparing specimens for viewingStaining: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.

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The electron microscope and further developments in the cell theoryThe 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.

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The electron microscope and further developments in the cell theoryThis 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 division5. All cells have the same basic chemical composition6. All energy flow (resulting from chemical reactions) of life occurs within cells.

healthmatters2day.blogspot.comFurther advances in microscopyCurrent 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.comHomeworkAnswer 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 advancementHand out Student Activity: Creating a table to compare light and transmission microscopes.