CELL STRUCTURE: Microscopes

What is an electron micrograph?
Photograph of an image seen using an electron microscope
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What is magnification?
The number of times larger an image appears, compared to the size of the object
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What is a photomicrograph?
Photograph of an image seen using an optical (light) microscope
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What is resolution?
The clarity of an image and the ability to distinguish between two points on an image. The higher the resolution, the clearer the image
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What are benefits of a light microscope?
Cheap, easy to use, portable, can be used in fields and labs, specimen can be alive
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What does the magnification on a light microscope tend to be?
1500X
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What is the resolution like in a light microscope?
Low, so they can't magnify any higher while giving a clear image
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How do you look at a specimen through a light microscope?
Place it on a slide, put the objective lens onto lowest magnification then look through the eyepiece lens
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How do you calculate total magnification?
total magnification = magnifying power of objective lens x magnifying power of the eyepiece lens
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How does a laser confocal scanning microscope work?
Uses lasers to scan an object point by point then uses a computer to assemble pixel information into one image on a screen
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Where are laser scanning microscopes used?
In medical professions and biological research
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What is the image produced by a laser scanning microscope like?
They have a high resolution and high contrast
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What are the two types of electron microscope?
Transmission electron microscope & scanning electron microscope
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How does a transmission electron microscope work?
A beam of electrons pass through the specimen, which is stained with metal salts. Some electrons pass through and focus on a screen/photographic plate.
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What is the magnification of a transmission electron microscope?
X2 million - developments are being made to increase this to X50 million.
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What is the electron micrograph of a TEM like?
2D and black & white
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How is the specimen for a TEM handled?
Must be chemically fixed by being dehydrated and stained
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How does a scanning electron microscope work?
Secondary electrons bounce off the specimens surface and are focused on a screen.
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What is the electron micrograph of a SEM like?
3D and black & white - but computers can add false colour
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What is the magnification of a SEM?
From x15 up to x200,000
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How must the specimen for a SEM be handled?
Has to be placed in a vacuum and is often coated with a fine film of metal
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What are some disadvantages of electron microscopes?
Very large, very expensive and need a great deal of skill and training to use them. Specimens must also be dead.
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Give some examples of specimens you can view under an optical microscope
Human blood, cheek cells, thin sections of tissue e.g. bone, leaf, root, fungal hyphae
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How can you observe an unstained, colourless specimen?
Some microscopes use light interference rather than absorbance, and some use a dark background to illuminate the specimen
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What are stains? (for staining specimens)
Chemicals that bind to molecules in/on the specimen making it easier to see
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What is differential staining?
When a stain binds to a specific cell structure
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What does iodine in potassium iodide solution stain? (in plants)
Turns cellulose in cell walls yellow
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What does iodine in potassium iodide solution stain? (in animals)
Turns starch granules blue/black
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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 acetic orcein stain?
Binds to DNA and stains chromosomes red
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What is the calculation for magnification?
Magnification = image size / actual size
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What is an eyepiece graticule?
A measuring device placed in the eyepiece and acts as a ruler when you view an object under the microscope
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What is a stage graticule?
A precise measuring device placed on the microscope stage to calibrate the value of eyepiece divisions
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Other cards in this set

Card 2

Front

What is magnification?

Back

The number of times larger an image appears, compared to the size of the object

Card 3

Front

What is a photomicrograph?

Back

Preview of the front of card 3

Card 4

Front

What is resolution?

Back

Preview of the front of card 4

Card 5

Front

What are benefits of a light microscope?

Back

Preview of the front of card 5
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