Microscope: Tortura Chapter 3 24-25

ocular lens

Eyepiece of a microscope: remagnifies the image formed by the objective lens

objective lens

Primary lens of the compound microscope that magnifies the specimen

Stage

holds the slide

Condenser

focuses light through the specimen

Diaphragm

Controls the amount of light entering the condenser

Illuminator

light source for the microscope

total magnification

objective lens x ocular lens

Resolution

the ability of the lenses to distinguish two points

refractive index

a measure of the light-bending ability of a medium

brightfield illumination

Dark objects are visible against a bright background

uses a condenser and diaphragm to concentrate light to view internal structures

darkfield microscopy

Light objects are visible against a dark background

Opaque disk placed in condenser

Only light reflected off the specimen enters the objective lens

Phase-contrast microscopy (PCM)

one set of light rays comes directly from the light source. The other set comes from the light that is reflected or diffracted from a particular structure in the specimen, good for viewing pellicles

Differential Interference Contrast Microscopy

Accentuates diffraction of the light that passes through a specimen; uses two beams of light and a prism to give a color 3D image

fluorescense microscopy

Uses UV light, Some organisms fluoresce naturally, others require fluorescent dyes

Confocal microscopy

a microscope that uses fluorescent stains and laser with blue light to view layers of specimens that are 100um thick

Transmission Electron Microscope (TEM)

A microscope that uses an electron beam to study the internal structure of thinly sectioned specimens.

Positive staining

surface of microbes are negatively charged and attract basic dyes

negative staining

microbe repels dye, the dye stains the background, leaving the organism white

Scanning Electron Microscope (SEM)

A microscope that uses an electron beam to scan the surface of a sample, coated with metal atoms, to give a 3D image of it's surface

Smear

a thin film of a solution of microbes on a slide

simple stain

single basic dye, all cells will have the same color--methylene blue

Differential stain

two or more dyes used to distinguish between different organisms.

Gram stain

A staining method that distinguishes between two different kinds of bacterial cell walls. Most widely used type of stain, four steps.

4 steps of gram stain

1. crystal violet

2. iodine (acts as a mordant)

3. alcohol wash--gram positive will retain color, gram negative will lose the dye (Gram positive are purple)

4. safranin--counterstain, gram negative cells will uptake this color--red

Mordant

agents that improve the binding of crystal violet dye in the cell

acid fast stain

a differential stain used to identify bacteria that are not decolorized by acid-alcohol (mycobacteria: tuberculosis and leprosy)

flagella staining

mordant applied to increase thickness of flagella

endospore stain

is applicable to only a few groups of bacteria AND usually shows the spores as green structures among a background of pink cells.

capsule stain

capsule remains unstained and forms a while ring around stained cell and background

-red/pink