Observing Microorganisms Through a Microscope

Question 1

Types of light microscopy

Answer 1

compound light microscopy

darkfield microscopy

phrase-contrast microscopy

fluorescence microscopy

confocal microscopy

Question 2

in a compound microscope the image from the objective lens is ______ again by the ______ lens

Answer 2

magnified

ocular

Question 3

Total magnification=

Answer 3

objective lens x ocular lens

Question 4

resolution

Answer 4

the ability of the lens to distinguish two points

Question 5

maximum resolution of a compound light microscope

Answer 5

0.2 um

Question 6

shorter wavelengths provide

Answer 6

greater resolution

Question 7

refractive index

Answer 7

a measure of the light-bending ability of a medium

Question 8

used to keep light from refracting

Answer 8

immersion oil

Question 9

dark field microscopy

Answer 9

light objects visible against dark background

opaque disk placed in condenser

only light reflected off the specimen enters the objective lens

Question 10

phrase contrast microscopy

Answer 10

allows examination of living organisms and internal cell structures

brings together two sets of light rays, direct rays and diffracted rays to form an image

Question 11

fluorescence microscopy

Answer 11

uses uv (short wavelength) light

fluorescent substances absorb uv light; emit longer wavelength (visible) light

stain cells with fluorescent dyes

Question 12

confocal microscopy

Answer 12

cells stained with fluorochrome dyes

short wavelength (blue) light excites a single plane of specimen

each plane of specimen is illuminated creating a three dimensional image

Question 13

electron microscopy

Answer 13

electrons instead of light

shorter wavelength of electrons = greater resolution

used for images too small for light microscopes

Question 14

transmission electron microscopy

Answer 14

magnifies objects 1000 to 10,000x

resolution of 10 nm

secondary electrons produce three dimensional image

electron gun produces beam of electrons; scans the surface of specimen

Question 15

basic dye

Answer 15

the chromophore is a cation

Question 16

acidic dye

Answer 16

chromophore is an anion

Question 17

negative staining

Answer 17

staining background instead of the cell

Question 18

simple stain

Answer 18

use of a basic dye

highlights entire microorganism

mordant=holds stain or coats specimen to enlarge it

Question 19

differential stains

Answer 19

used to distinguish between bacteria

Two types: gram stain, acid-fast stain

Question 20

gram positive

Answer 20

bacteria has thick peptidoglycan cell walls

retain the crystal violet stain; appear purple

Question 21

gram negative

Answer 21

bacteria has a thin peptidoglycan cell wall

layer of lipopolysaccharides

do not retain crystal violet; counterstained to appear pink

Question 22

acid fast stain

Answer 22

binds only to bacteria that have a waxy material on their cell walls

not decolorized by acid alcohol

used for identification of: mycobacterium and nocardia

Question 23

negative staining for capsules

Answer 23

capsules= covering; does not accept most dyes

Question 24

Endospore staining

Answer 24

endospores= resistant, dormant structures; cannot be stained by ordinary methods

Question 25

endospore staining: Primary stain

Answer 25

malachite green; usually with heat

Question 26

endospore staining: decolorize cells

Answer 26

water

Question 27

endospore staining: counterstain

Answer 27

safranin (like with gram negative, that is why it appears pink)

Question 28

spores will appear green within…..

Answer 28

red or pink cells