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24 Cards in this Set
- Front
- Back
How do you prepare a dry mount? |
•Solid specimens viewed whole or cut into thin slides with a thin blade •Specimen placed on top of the slide in the centre •Cover slip placed ontop |
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How is a wet mount prepared |
•Specimens suspended in liquid •Cover slip placed on at an angle |
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How is a squash slide prepared |
•Wet mount first prepared •A lens tissue used to gently press down the cover slip |
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How is a smear slide prepared? |
•Edge of a slide used to smear the sample •Cover slip then placed over the sample |
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Bright field microscopy |
Sample is illuminated from below and viewed from above |
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Wide-field microscopy |
Whole sample is illuminated at once |
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In basic light microscopy why do cells tend to have a low contrast? |
Cells do not absorb a lot of light |
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How do stains increase contrast and therefore allow them to be distinguishable |
•Different stains take up stains differently •increased contrast allows components to become visible so they can be identified |
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How do you prepare for staining? |
•Sample must be placed in slide and allowed to airdry •Is then heat fixed by being passed through the flame •Specimen will adhere to the slide and take up the stain |
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Give two examples of positively charged dyes and how do they work? |
•Crystal violet or methyl blue •Attracted to negatively charged materials in cytoplasm •Leads to staining of components |
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Give two examples of negatively charged dyes and how do they work? |
•Nigrosin and congo red •Repelled by negatively charged cytosol •Stays outside cells, leaving them unstained •Stand out against stained background |
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What is differential staining? |
•A technique that allows the differentiation of two types of organisms that would otherwise be hard to identify •Can also differentiate between different organelles of a single organism within a tissue sample |
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What is gram stain technique? |
•Used to seperate bacteria into two groups, gram positive and gram negative |
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How do you prepare for gram staining |
•Crystal violet forst applied to bacteria on a slide •Then iodine is applied which fixed the dye •Slide is washed with alcohol |
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After preparing for gram staining how do you distinguish the bacteria? |
•Gram positive bacteria retain the crystal violet stain and appear blue or purple under a microscope •Gram negative bacteria have thin cells walls and lose the stain |
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What happens to gram negative bacteria after they lose the crystal violet stain? |
•They are stained with safranin dye which is a counterstain •They then appear red under the microscope |
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What type of bacteria is susceptible to penicillin and why? |
•Gram positive •Because penicillin inhibits the formation of cell walls and they need thicker ones |
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What is acid fast technique used for? |
Used to differentiate species of mycobacterium from other bacteria |
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How are cells prepared for acid fast technique? |
•A lipid solvent is used to carry carbolfuchsin dye into the cells being studied •Cells are then washed with dilute acid-alcohol solution |
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What are the results of the acid fast technique? |
•Mycobacterium are not affected by acid-alcohol and retain the stain which is bright red •Other bacteria lose the stain and are exposed to methlyene blue stain, which is blue |
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Fixing |
Chemicals like formaldehyde are used to preserve specimens in as near-natural a stae as possible |
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Sectioning |
Specimens are dehydrated with alcohols and then placed in a mould with wax or resin to form a hard block |
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Staining |
Specimens are often treated with multiple stains to show different structures |
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Mounting |
Specimens are secured to a microscope slide a cover slip is placed on top |