Chapter 2

Question 1

Light microscopes

Answer 1

use visible light to illuminate specimens, use glass lenses to focus, have light pass through specimen

Question 2

resolution

Answer 2

the ability to distinguish two close, adjacent objects as separate and distinct. determined by the wavelength of light used and the lenses used. Shorter wavelenghth= greater resolution

Question 3

Bright field microscope

Answer 3

specimens are visualized because of differences in contrast between specimen and surroundings. Entire field illuminated. Produces a dark image against a brighter background.
Requires staining objects to achieve sufficient contrast between specimen and surroundings medium.

Question 4

Dark field microscope

Answer 4

uses special condenser lens. image is formed by light reflected or refracted by specimen. bright image of the object against a dark background. Used to observe living, unstained preperations. (negative staining)

Question 5

Phase-Contrast Microscope

Answer 5

Converts slight differences in refractive index and cell density into easily detected variations in light intensity.Used to observe living cells. Studying microbial motility, detecting bacterial structures such as endospores and inclusion bodies that have refractive indices different from that of water

Question 6

Fluorescence Microscope

Answer 6

Used to visualize specimens that fluoresce after exposure specimen to ultraviolet, violet, or blue light. (Autofluorescence). Shows a bright image of the object resulting from the flruoescent light emitted by the specimen.

Question 7

Differential Interference Contrast Microscope

Answer 7

Creates image by detecting differences in refractive indices and thickness of different parts of specimen. Observe living cells, live unstained cells appear brightly colored and 3D. cell walls, endospores, granules, vacuoles, and nuclei are clearly visible

Question 8

Confocal microscopy

Answer 8

confocal scanning laser micrsocopy creates sharp, composite 3D image of specimens by using laser beam, aperture to eliminate, stray light and computer interface. Numerous applications including study of biofilms.

Question 9

Chromophore

Answer 9

coloring ion

Question 10

Simple stain

Answer 10

use can determine size, shape, and arrangement of bacteria

Question 11

differential stains

Answer 11

2 or more dyes. several steps. gram stain and acid fast stain. Used tod etect presence or absence of structures (endospores, flagella, capsules)

Question 12

Endospore staining

Answer 12

heated, double staining technique. Bacterial endospore is one color and vegetative cell is a different color.

Question 13

Capsule Stain

Answer 13

used to visualize capsules surrounding bacteria. Negative stain- capsules may be colorless against a stained background.

Question 14

Flagella staining

Answer 14

mordant applied to increase thickness of flagella

Question 15

electron microscopy

Answer 15

uses electrons instead of light as the illuminated beam. Illumination-electron beam, lenses-magents, image-photograph or computer, stains-metals

Question 16

Transmission Electron Microscope

Answer 16

beam of electrons pass through specimen. Electromagents function as lenses. Electrons scatter when they pass through thin sections of a specimen. Transmitted electrons are under vacuum which reduces scatter and are used to produce clear image. Denser regions in specimen, scatter more electrons and appear darker. Enables visualization of structures at the molecular level.

Question 17

Negative stain

Answer 17

heavy metals do not penetrate the specimen but render dark background. used for study of viruses, bacterial gas vacuoles.

Question 18

shadowing

Answer 18

coating specimen with a thin film of a heavy metal on only one side. useful for viral morphology, flagella, dna

Question 19

freeze-etching

Answer 19

freeze specimen then fracture along lines or greatest weakness. allows for 3D observation of shapes of intracellular structure. reduces artifacts

Question 20

electron cryotomography

Answer 20

rapid freezing technique provides way to preserve native state of structure examined in vacuum. images are recorded from many different directions to create 3D structures. extremely high resolution images of cytoskeletal elements, magnetosomes, inclusions bodies, flagellar motors, viral structures

Question 21

scanning probe microscopy

Answer 21

steady current (tunneling current) maintained between microscope probe and specimen. up/down movement of probe as it maintains current Is detected, used to create image of surface of specimen

Question 22

contaminant

Answer 22

any unwanted microorganism in the medium

Question 23

asceptic technique

Answer 23

sterile, anything done to minimize contamination