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31 Cards in this Set
- Front
- Back
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What is an electron micrograph?
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A photograph of an image seen using an electron microscope
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Define magnification?
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The number of times larger an image appears compared with the size of the object
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Define organelles?
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Small structures within cells, each of which has a specific function.
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Define photomicrograph?
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Photograph of an image seen using an optical microscope
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Define resolution?
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The clarity of an image; the higher the resolution the clearer the image
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Where are optical microscopes commonly used?
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Schools, colleges, hospitals and research laboratories
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What are the advantages of optical microscopes?
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they are relatively cheap. Easy to use portable can be used in the field as well as in labs can be used to study whole living specimens |
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What are the disadvantages of optical microscopes?
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Rely on lenses to focus a beam of light only allow magnification up to x1500 or sometimes x2000 they have limited resolution structures closer together than 20nm diameter will appear as one object |
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How do you calculate the total magnification of an optical microscope?
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Magnifying power of the objective lens x magnifying power of the eyepiece lens
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How do laser scanning (confocal) microscopes work?
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use a laser light to scan an object and assemble the pixel information into one image (displayed on a computer screen)
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What are the advantages of using laser scanning microscopes?
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High resolution and high contrast have depth selectivity |
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How do electron microscopes work?
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Use a beam of electrons fired from a cathode and focused by magnets
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What are the features of an electron micrograph produced using a transmission electron microscope (TEM)?
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The electrons form a 2D black and white image Produce a magnification up to 2million times |
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How does a scanning electron microscope (SEM) work?
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Electrons do not pass through the specimen, cause secondary electrons to bounce off the specimen surface and be focused onto a screen.
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What are the features of an electron micrograph produced by a SEM?
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3D image with magnification from x15 to x200000 images are black and white |
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What are the disadvantages of using a TEM?
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Very large and very expensive needs skill and training to use specimen must be dehydrated and stained |
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What are the disadvantages of using a SEM?
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Specimens must be placed in a vacuum very large and very expensive needs skill and training to use |
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What is a stain?
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Coloured chemicals that bind to molecules in or on a specimen
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What is differential staining?
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Some stains bind to specific cell structures |
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What does the stain Acetic orcein bind to and what colour is it?
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Acetic orcein binds to DNA and stains chromosomes dark red |
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What does the stain Eosin bind to?
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Cytoplasm |
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What does the stain Sudan bind to? |
Lipids |
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What does the iodine in potassium iodine solution stain in cells?
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Stains the cellulose in plant cell walls yellow and starch granules blue/black |
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How are prepared and permanently fixed slides prepared?
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Specimens are dehydrated, embedded in wax to prevent distortion during slicing. Using a special instrument to make very thin slices call sections - these are stained and mounted in a special chemical to preserve them
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How can you calculate the actual size of a specimen by looking at a photomicrograph when you know the magnification?
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measure the specimen in the photomicrograph in mm. Convert into micro metres (x1000). Divide this by the magnification. |
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What is an eyepiece graticule?
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A transparent eyepiece with a small ruler etched onto it. Enables a specimen to be measured in eyepiece units. the scale represents different lengths at different magnifications. |
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How can an eyepiece graticule be calibrated?
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Each eyepiece division = length on stage graticule / length on eyepiece graticule |
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What is a prokaryotic cell?
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cells which lack membrane bound organelles and an organised nucleus
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What is a eukaryotic cell?
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cells which have a true nucleus
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What are the differences between prokaryotic and Eukaryotic cells?
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Eukaryotic have a more well developed cytoskeleton with centrioles. Prokaryotic do not have a nucleus or membrane bound organelles (e.g. mitochondria or chloroplasts). Both can have cell walls but prokaryotic is made of peptidoglycan not cellulose. Eukaryotic have larger ribosomes. Prokaryotic have naked DNA that floats free in the cytoplasm as a loop. Eukaryotic have linear chromosomes. Some prokaryotic have a protective waxy cuticle, or plasmids, or flagella, or pili. |
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How do prokaryotic cells divide?
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Binary fission (not mitosis because they don't have linear chromosomes) |
