Microbiology Chapter 2

Front 1

Refraction

Back 1

Bent

Front 2

Focal point

Back 2

Light rays are focused at a specific place

Front 3

Focal Length

Back 3

Distance between the center of lens and the focal point

Front 4

Short focal length?

Back 4

More magnification

Front 5

Refractive index

Back 5

A measure of how greatly a substance slows the velocity of light.

When light passes from air to glass, it is bent and slowed

Front 6

4 Major types of light microscopes?

Back 6

1. Brightfield
2. Darkfield
3. Phase-contrast
4. Fluorescent

Front 7

Parfocal

Back 7

Microscope remains in focus when objectives are changed

Front 8

Resolving power

Back 8

Ability of a lens to distinguish small objects that are close together

Front 9

Working distance

Back 9

Distance betwee the front surface of lens and the surface of cover glass or specimen. (amount you can move the lens up and down)

Front 10

Total magnification

Back 10

Product of the ocular lens X the objective lens

Front 11

What two factors determine the resolving power of a light microscope?

Back 11

1. Wavelength of light (shorter=greater)
2. Numerical aperature

Front 12

Which color of light would provide the best resolving power, blue or red?

Back 12

Blue

Front 13

What are the basic features of a darkfield microscope?

Back 13

Produces a bright image of the object against a dark background. Better contrast between dark & light. Able to determine motility.

Front 14

Is the resolving power of a darkfield microscope better than that of a brightfield microscope?

Back 14

Yes, darkfield has better contrast

Front 15

What are the basic features of a phase contrast microscope?

Back 15

Enhances the contrast between intracellular structures having slight differences in refractive index. Excellent way to observe living cells. Able to determine motility.

Front 16

Describe a fluorescence microscope.

Back 16

Specimens usually stained with fluorochromes. Shows a bright image of the object resulting from the fluorescent light emitted by the specimen.

Front 17

What kind of light is used in a fluorescent microscope?

Back 17

Ultraviolet, violet, or blue light.

Front 18

Why are microbiology specimens stained before viewing under a microscope?

Back 18

-Increases visibility of specimen
-Accentuates specific morphological features (flagella so narrow you cant see them without staining)
-Preserves specimens

Front 19

Heat fixing

Back 19

Used routinely with procaryotes. Preserves overall morphology but not internal structures.

Front 20

What is a differential stain?

Back 20

Divides microorganisms into groups based on their staining properties.

Front 21

Why is a differential stain used?

Back 21

Important becase it allows you to distinguish between major groups of Bacteria.

Front 22

Gram stain

Back 22

Most widely used differential staining procedure. Divides Bacteria into two groups based on differences in cell wall strucutre. Gram staining is less useful for Archaea (many different cell wall structures).

Front 23

Acid-fast Stain

Back 23

Used to identifiy mycobacteria

Front 24

Why is the acid-fast stain necessary?

Back 24

Mycobacteria contains lipids within and so it doesn't take up other stains

Front 25

Mycobacterium

Back 25

Mycobacterium tuberculosis-causes tuberculosis

Mycobacterium leprae-causes leprosy

Front 26

Negative staining

Back 26

Used to visualize capsules surrounding bacteria. Capsules are colorless against a stained background.

Front 27

Endospore staining

Back 27

Double staining technique. Bacterial endospore is one color and vegetative cell is a different color.

Front 28

Flagella staining

Back 28

Mordant applied to increase thickness of flagella

Front 29

Transmission Electron Microscope

Back 29

Transmitted electrons (those that do not scatter) are used to produce an image. Denser regions in specimen, scatter more electrons and appear darker.

Front 30

Why is the resolving power of the electron microscope greater than that of a light microscope?

Back 30

Wavelength of electron beam is much shorter than light, resulting in much higher resolution.

Front 31

How are specimens prepared for electron microscopy?

Back 31

For transmission, specimens must be dried, embedded in plastic, cut very thin.
Specimens are chemically fixed and stained with electron dense material.

Front 32

Shadowing

Back 32

Coating specimen with a thin film of heavy metal

Front 33

Freeze-etching

Back 33

Freeze specimen then fracture along lines of greatest weakness

Front 34

Scanning Electron Microscope

Back 34

Uses electrons reflected from the surface of a specimen to create a 3D image.

Front 35

Confocal Microscope

Back 35

Confocal scanning laser microscope. Laser beam used to illuminate spots on specimen. Computer complies images created from each point to generate a 3D image.

Front 36

Advantage of confocal microscopy?

Back 36

Have extremely high resolution and can be used to observe individual atoms. 3D.