The number of times larger an image is compared to the original object
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How do we calculate the total magnification an optical microscope provides?
total magnification = magnifying power of the objective lens x magnifying power of the eyepiece lens
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How do we calculate the magnification of an image?
magnification = image size / actual size
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What is resolution?
The ability of an optical instrument to distinguish between two points and produce an image that shows fine detail clearly
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What are the advantages of optical microscopes?
cheap; easy to use; portable (can be used in the field); able to study the whole, live specimen
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What is the maximum magnification of an optical microscope?
x1500 (some up to x2000)
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How does a laser scanning (confocal) microscope produce a high resolution, high contrast image?
They scan an object point by point using laser light and a computer assembles an image from the pixel information and displays it on a screen
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They have depth selectivity, what does this mean?
They can focus on structures at different depths within a specimen
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Can they be used to clearly observe whole, living specimens and cells?
yes
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They can be used in many areas of biological research, how can they be used in the medical profession?
e.g. to give a swift diagnosis and therefore earlier, more effective treatment to patients with fungal corneal infection
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How do electron microscopes produce images?
A beam of fast travelling electrons are fired from a cathode and focused by magnets onto a screen or photographic plates
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What is the wavelength of electrons and what does this mean for the resolution of electron microscopes compared to that of optical microscopes?
0.004nm and this means that the resolution is much better than that of optical microscopes
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What is the magnification of transmission electron microscopes?
x2 million (new generations up to x50 million)
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What type of image does a transmission electron microscope produce?
2D black and white because the electrons pass through the specimen and are focused onto a screen/photographic plate
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How is a specimen prepared for a TEM?
The specimen is chemically fixed by being dehydrated and stained with metal salts. It is then placed in a vaccum.
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What type of image is produced by a scanning electron microscope and why?
A 3D black and white (computers can add false colour) image because the electrons are reflected from the surface of the specimen.
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How is a specimen prepared for an SEM?
It is often coated with a fine film of metal and then placed in a vaccum.
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What is the maximum magnification of an SEM?
x200, 000
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What are the disadvantages of electron microscopes?
Expensive; Large; Need a lot of training to use; specimens have to be dead because they are in a vaccum
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What is differential staining?
Stains that bind to specific cell structures, staining each structure differently so the structure can be easily identified within a single preperation
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What is methylene blue?
An all purpose stain.
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What does acetic orcein bind to?
DNA and stains chromosomes dark red.
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What does sudan red stain?
lipids
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What does eosin stain?
cytoplasm
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What does iodine stain?
Stains cell walls yellow and starch granules blue/black.
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How are permanently fixed slides prepared?
The specimen is dehydrated; embedded in wax (to prevent distortion when slicing); sections are made with a special instrument; the specimen is stained, mounted and chemically preserved
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Other cards in this set
Card 2
Front
How do we calculate the total magnification an optical microscope provides?
Back
total magnification = magnifying power of the objective lens x magnifying power of the eyepiece lens
Card 3
Front
How do we calculate the magnification of an image?
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