what is the difference between magnification and resolution
magnification describes how many times bigger an image gets when it is put under a microscope and resolution is the microscopes ability to distinguish between two points
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what is resolution
the smallest distance that two objects can be apart wile still appearing as two objects
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advantages of light microscope
they are cheap, easy to use, they can be used to study living cells
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disadvantages of light microscope
2D image of living cells, visible light to create an image, resolution of 200nm and magnification of x2000
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how do laser scanning microscopes present an image
the laser passes over each point in the specimen and creates an image overtime
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advantages of laser scanning microscope
can show images in 3d
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disadvantages of laser scanning microscope
more expensive than light microscopes
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how do electron microscopes work
use a beam of electrons to study specimens
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how do they produce high resolution images
electrons have a higher wavelength and so can be used to create higher resolution images
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what are the two types of electron microscopes
SEM and TEM
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disadvantages of SEM
specimen must also be stained or coated with metal and placed in a vacuum, the specimen can only be prepared if dead
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advantages of SEM
image can be 3D however lower resolution than TEM
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how do SEM view the specimen
the electron beam hits the surface of the specimen and bounces off to produce the picture
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how do TEM produce image
the electron travels right through the specimen to a detector below
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advantages of TEM
higher resolution and magnification however only viewed in 2D
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differences of SEM and TEM
scanning is in 3D while transmission in 2D - SEM max magnification is x200,000 whilst TEM is x2,000,000 - SEM max resolution is 20nm whilst TEM is 0.1nm
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what is the magnification formula
magnification = image size/actual size
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why is staining used
to highlight cells in the microscope
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what stain is used for the nucleus
Acetic orcein - the dye molecule binds to the DNA
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what stain is used for starch granules and what colour does it go and can it be used for other cell structures
iodine starch granules dark purple and cell walls yellow
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Describe how a transmission electron microscope (TEM) works.
Pass a high energy beam of electrons through a thin slice of specimen. 2. More dense structures appear darker since they absorb more electrons. 3. Focus image onto fluorescent screen or photographic plate using magnetic lenses.
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Describe how light microscopes work.
Lenses focus rays of light and magnify the view of a thin slice of specimen. 2. Different structures absorb different amounts and wavelengths of light. 3. Reflected light is transmitted to the observer via the objective lens and eyepiece.
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Describe how a scanning electron microscope (SEM) works.
Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses. 2. Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
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Why do samples need to be stained for light microscopes?
Coloured dye binds to the structures. Facilitates absorption of wavelengths of light to produce image. Differential staining: contrast between heavily & lightly stained areas distinguishes structures
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State the magnification and resolution of a compound light microscope.
magnification: x 2000 resolution: 200 nm
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State the magnification and resolution of a TEM.
magnification: x 500 000 resolution: 0.5 nm
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State the magnification and resolution of an SEM.
magnification: x 500 000 resolution: 3 - 10 nm
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Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure.
Place micrometer on stage to calibrate eyepiece graticule. 2. Line up scales on graticule and micrometer. Count how many graticule divisions are in 100μm on the micrometer. 3. Length of 1 eyepiece division = 100μm / number of divisions. 4. Use calib
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What are bacterial and fungal cell walls made of?
bacteria: peptidoglycan (murein) fungi: chitin
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Other cards in this set
Card 2
Front
what is resolution
Back
the smallest distance that two objects can be apart wile still appearing as two objects
Card 3
Front
advantages of light microscope
Back
Card 4
Front
disadvantages of light microscope
Back
Card 5
Front
how do laser scanning microscopes present an image
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