Chapter 2 : Microscopy

Question 1

What type of microscope was first invented and is the most widely used today?

Answer 1

Light microscope

Question 2

What is the resolution limit in a light microscope?

Answer 2

0.2 um ( micrometer)

Question 3

what is refractive index?

Answer 3

a measure of how much a substance slows the velocity of light

Question 4

When light passes from one medium to another, what happens to the light?

Answer 4

refracted (bent)

Question 5

In regards to lenses they focus light rays at a specific place called?

Answer 5

focal point

Question 6

what kind of microscope would be used to observe stained or unstained specimens to produce a dark image with a bright background and have different magnification?

Answer 6

Bright-field Microscope

Question 7

what is total magnification?

Answer 7

the product of ocular lenses and objective lenses

Question 8

The ability of a lens to distinguish objects from each other rather than a single larger object is ?

Answer 8

Resolution

Question 9

the shorter the wavelength their is less resolution T or F?

Answer 9

F The greater the resolution

Question 10

what is the distance between the front surface of the lens and the surface of the cover glass or specimen when it is in sharp focus called?

Answer 10

working distance

Question 11

what three microscopes may be used to gain better contrast between the cells and it structures ?

Answer 11

dark field
phase contrast
differential interference contract
(DIC)

Question 12

what kind of microscope would produce a bright image against a dark background?

Answer 12

Dark field Microscope

Question 13

How is the image produced in a Dark field microscope?

Answer 13

light being refracted or reflected by specimen

Question 14

How is the image produced in a phase contrast microscope ?

Answer 14

produces an image of a darker microbe against a lighter background?

Question 15

How does DIC microscopes create images ?

Answer 15

detect differences in refractive indices and thickness in different part of specimen

Question 16

In a fluorescence microscopes how is the image produced?

Answer 16

by exciting a specimen with a wavelength of light that triggers the object to emit fluorescence light

Question 17

In a fluorescence microscope what do we use to stain the microbe?

Answer 17

fluorochromes - absorb and emit visible fluorescent light

Question 18

What are fluorochromes?

Answer 18

labeled probes- antibodies or fluorochrome tags

Question 19

Why do we prepare and stain specimen?

Answer 19

increase visibility
accentuate specifics in morphology
preservation specimen

Question 20

Scientists want stained cells to resemble living cells as closely as possible, what process is used to preserve the internal and external structures?

Answer 20

Fixation

Question 21

How does Fixation preserve internal and external structures?

Answer 21

By inactivating enzymes that tell cell morphology to toughen up

Question 22

There are two type of heat fixation, what are they?

Answer 22

Heat fixation: preserves morphology but destroys subcell structures
Chemical fixation: protects fine sub cell structure and morphology

Question 23

Ionizable dyes have charged groups, basic dye have negative charge and acidic dyes have positive charges T o F ?

Answer 23

False
basic +
Acidic -

Question 24

Describe what simple staining is?

Answer 24

• Uses one stain
• used to determine size, shape and bacteria arrangement

Question 25

Describe what differential staining does ?

Answer 25

divides organisms into groups based on staining

Question 26

Gram stain and acid fast stain are what kind of staining ?

Answer 26

differential staining

Question 27

differential staining is used to detect the presence or absence of what structures?

Answer 27

Capsules and flagella

Question 28

what are the differences between a gram-positive bacteria and a gram-negative bacteria?

Answer 28

gram + have a thicker peptidoglycan layer
gram - have an outer membrane and an inner membrane with a thin peptidoglycan layer

Question 29

Why is acid-fast staining more useful for staining bacteria members of myobacterium?

Answer 29

due to having a cell wall of lipids, it prevents dye to bind

Question 30

Capsule staining is used for?

Answer 30

used to visualize polysaccharide capsules around bacteria

Question 31

How may capsules appear in negative staining ?

Answer 31

colorless against stained background

Question 32

what is used to provide information about the presence and distribution pattern of flagella?

Answer 32

flagella staining

Question 33

The electron wavelength is 100,00x shorter than visible light, resulting in a higher resolution image T o F?

Answer 33

True

Question 34

what occurs in electron microscopy?

Answer 34

electrons replace the light as a beam

Question 35

how does TEM work?

Answer 35

electrons pass through the specimen to form image

Question 36

How does SEM work to produce an image?

Answer 36

uses excited electrons from the surface of specimen to make image

Question 37

What is the purpose for Cryo-electron microscopy?

Answer 37

used to see biomolecules like proteins to see high resolution structures