Study Guide Chapter 3 Done

Question 1

Metric System Conversions

Answer 1

M->mm->um->nm

Question 2

Define light microscopy

Answer 2

Any kind of microscope tat uses visible light to observe specimens

Question 3

Describe the parts of a compound microscope

Answer 3

Ocular lens
Body tube
Arm
Objective lens
Stage
Condeser
Diaphragm
Illuminator
Course focues
base
Fine focus

Question 4

Differentiate between ocular lens, objective lens, brightfield microscopy, magnification and resolution and resolving power

Answer 4

Ocular lens: eyepiece

Objective lens: lenses that magnify the specimen

Bright field Microscopy: Specimen visible against a bright background;light reflected off the specimen

Magnification: ability to enlarge the image of an object

Resolution: Ability of the lenses to distinguish two points

Resolving Power: Ability to show detail

Question 5

Calculate total mag

Answer 5

Objective X Ocular lenses

Question 6

Explain the difference between brightfield and darkfield microscopy:

Answer 6

o Brightfield microscopy: specimen visible against a bright background; light reflected off the specimen does not enter the objective lens
o Darkfield microscopy: specimen visible against dark background due to opaque condenser; only the light reflective off the specimen enters the objective lens

Question 7

Differentiate between phase-contrast, differential, fluorescence and confocal microscopy and describe what they are used for.

Answer 7

o Phase-Contrast:
 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
o Differential:
 Uses two light beams and prisms to split light beams, giving more contrast and color to the specimen
 Greater resolution
o Fluorescence:
 Uses UV (short wavelength) light
 Fluorescent substances absorb UV light and emit longer wavelength (visible) light
o Confocal Microscopy:
 Cells are stained with fluorochrome dyes
 Each plane in a specimen is illuminated and a three-dimensional image is constructed with a computer
 Can examine layers of cells to a depth of 100 μm

Question 8

Explain how electron microscopy differs from light microscopy.

Answer 8

Electron Microscopy uses electrons instead of light
highest mag 1,000-10,000,000

Question 9

• Differentiate between and identify uses for the transmission electron microscope (TEM) and the scanning electron microscope (SEM).

Answer 9

o Transmission Electron Microscopy (TEM) – for internal structures
o Scanning Electron Microscopy (SEM)- for surface structures

Question 10

Describe wet mount, smear, fixation and staining are.

Answer 10

o Wet Mount:
 Liquid placed on slide and covered with coverslip
o Smear:
 A thin film of a material containing microorganisms spread over a slide
o Fixation:
 Microorganisms are attached to the slide by a combination of heat and air, which kills them and preserves them from decay and lysis
o Staining:
 Coloring microorganisms with a dye that emphasizes certain structures

Question 11

Differentiate between acidic and basic dyes and between simple and negative stain.

Answer 11

o Basic Dyes:
 The Chromophore is a cation
 Will adhere to the bacterial cell membrane because the latter is negatively charged
o Acidic Dyes;
 The Chromophore is an anion
* Will adhere to the microscope slide because the latter is positively charged
o Negative Stains:
 Capsules are a gelatinous polysaccharide layer secreted ouside the cell wall that do not accept most dyes

Question 12

Differentiate between simple, differential and special staining , explain their purpose and give examples of each.

Answer 12

Simple Stains:
 Use of a single basic dye
 Highlights the entire microorganism to visualize cell shapes and arrangement
 Example: Methylene Blue

Differential Staining:
 Used to distinguish between bacteria
 Examples: Gram stain, Acid-fast stain

Special Staining:
 Binds only to bacteria that have a waxy material (mycolic acid) in their cell walls, which is not decolorized by acid-alcohol
 Used for the identification of:
* Mycobacterium
* Nocardia
 Examples: Capsule Stain

Question 13

Describe capsule, endospore stain and flagella stains.

Answer 13

Capsule:
 gelatinous polysaccharide layer secreted outside the cell wall that do not accept most dyes

Endospore Stains:
 resistant, dormant structures inside some cells that cannot be stained by ordinary methods

Flagella Stain:
 Flagella are structures of locomotion
 Leifson Dye: Uses a combination of simple dyes and a mordent to thicken appearance of flagella making them visible under the light microscope

Question 14

List the steps of the Gram stain and describe the appearance of gram-positive and gram- negative stains after each step.

Answer 14

o Add Chrystal violet to smear
o Rinse with water
o Add iodine (mordent)
o Rinse with water
o Add alcohol (decolorization)
o Add Safranin (counterstain)

Question 15

Compare and contrast Gram-stain and acid-fast stain.

Answer 15

o Gram stain is based on cell wall while acid fast is based on the presences of mycolic acid