Microscopy

Front 1

How do you prepare a dry mount?

Back 1

•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

Front 2

How is a wet mount prepared

Back 2

•Specimens suspended in liquid

•Cover slip placed on at an angle

Front 3

How is a squash slide prepared

Back 3

•Wet mount first prepared

•A lens tissue used to gently press down the cover slip

Front 4

How is a smear slide prepared?

Back 4

•Edge of a slide used to smear the sample

•Cover slip then placed over the sample

Front 5

Bright field microscopy

Back 5

Sample is illuminated from below and viewed from above

Front 6

Wide-field microscopy

Back 6

Whole sample is illuminated at once

Front 7

In basic light microscopy why do cells tend to have a low contrast?

Back 7

Cells do not absorb a lot of light

Front 8

How do stains increase contrast and therefore allow them to be distinguishable

Back 8

•Different stains take up stains differently

•increased contrast allows components to become visible so they can be identified

Front 9

How do you prepare for staining?

Back 9

•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

Front 10

Give two examples of positively charged dyes and how do they work?

Back 10

•Crystal violet or methyl blue

•Attracted to negatively charged materials in cytoplasm

•Leads to staining of components

Front 11

Give two examples of negatively charged dyes and how do they work?

Back 11

•Nigrosin and congo red

•Repelled by negatively charged cytosol

•Stays outside cells, leaving them unstained

•Stand out against stained background

Front 12

What is differential staining?

Back 12

•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

Front 13

What is gram stain technique?

Back 13

•Used to seperate bacteria into two groups, gram positive and gram negative

Front 14

How do you prepare for gram staining

Back 14

•Crystal violet forst applied to bacteria on a slide

•Then iodine is applied which fixed the dye

•Slide is washed with alcohol

Front 15

After preparing for gram staining how do you distinguish the bacteria?

Back 15

•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

Front 16

What happens to gram negative bacteria after they lose the crystal violet stain?

Back 16

•They are stained with safranin dye which is a counterstain

•They then appear red under the microscope

Front 17

What type of bacteria is susceptible to penicillin and why?

Back 17

•Gram positive

•Because penicillin inhibits the formation of cell walls and they need thicker ones

Front 18

What is acid fast technique used for?

Back 18

Used to differentiate species of mycobacterium from other bacteria

Front 19

How are cells prepared for acid fast technique?

Back 19

•A lipid solvent is used to carry carbolfuchsin dye into the cells being studied

•Cells are then washed with dilute acid-alcohol solution

Front 20

What are the results of the acid fast technique?

Back 20

•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

Front 21

Fixing

Back 21

Chemicals like formaldehyde are used to preserve specimens in as near-natural a stae as possible

Front 22

Sectioning

Back 22

Specimens are dehydrated with alcohols and then placed in a mould with wax or resin to form a hard block

Front 23

Staining

Back 23

Specimens are often treated with multiple stains to show different structures

Front 24

Mounting

Back 24

Specimens are secured to a microscope slide a cover slip is placed on top