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8 Cards in this Set
- Front
- Back
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Magnification |
The number of times greater greater an image is than the object Enlarge the image but does not increase the level of detail |
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Resolution |
Ability to see two distinct points separately |
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Metre (m) 1 Decimetre (dm) 0.1 Centimetre (cm) 0.01 Millimetre (mm) 0.001 Micrometre (μm) 0.000 001 Nanometre (nm) 0.000 000 001 |
Ｉmage size = Actual size × Magnification |
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The light microscope |
Magnification: max ×1500 Resolution: 0.02 μm/200nm (half the wavelenght of the light)
Wide range of specimen (Euglena, Daphnia) Can't give a detailed information about internal cell structure
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Transmission electron miscroscope (TEM)
Magnification: more than ×500 000 Resolution: 0.0001μm/0.1 nm
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1, The electron beam passes through a very thin prepared sample.
2,Denser parts of the specimen absorb more electrons so it gives some contrast.
3, The final image produced is two dimensional.
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Scanning electron microscope (SEM)
Magnification: more than ×100 000 Resolution: 0.0001μm
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1, SEMs scan a sample with a beam of primary electrons that knock electrons from its surface. 2, These secondary electrons are picked up by a collector, amplified, and transmitted onto a viewing screen. 3, The image produced is 3-D, however, it only shows its outside surface only. |
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Advantages of the electron microscope
◦The resolution is 0.2nm (×1000 more than in the light microscope) ◦Therefore, it can be used to produce detailed imaes of the structures (organelles) inside cells. ◦SEM produces 3D images that can reveal the detail of contours and cellular or tissue arrangements - this is not possible using light microscope |
Limitations of the electron microscope
◦Electron beams are deflected by the molcecules in air, so samples have to be placed in a vacuum. ◦Electron microscopes are extremely expensive items. ◦Preparing samples and using an electron microscope both require a high degree of skill and training.
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Preparation for Light microscope
◦ Samples are stained with coloured stains that bind to certain chemicals on or in the specimen. e.g. Acetic Orcein stains DNA dark red. ◦Samples may be sectioned - embedded in wax; this helps with preserving structure while cutting. e.g. soft tissue such as brain |
Preparation for Electron Microscope ◦Stabilising an organism's mobile macrostructure ◦Freezing the sample very rapidly to preserve its state ◦Dehydrate it to replace the water with ethanol ◦Embed the dehydrated tissue in a solid resin ◦Sectioning using a diamond knife ◦Stain it using lead salts to scatter electrons differently so it gives contrast ◦mount it on a copper grid |
