Module 1

Question 1

Light microscopes utilize lenses to

Answer 1

bend light beams to focus and magnify the sample

Question 2

how do bright field microscopes work

Answer 2

a light source shines through the bottom of the sample.

Question 3

what is resolution

Answer 3

the ability to ditinguish a point from neighboring points

Question 4

the physical limit for resolution is dictated by what?

Answer 4

the wavelength of light

Question 5

what is immersion oil used for ?

Answer 5

as a way to prevent refraction and maximize light passing trough the sample

Question 6

What is contrast?

Answer 6

being able to differentiate the background from the object being viewed.

Question 7

how do scientist achieve contrast and what is the downside?

Answer 7

through staining, it often kills the sample

Question 8

how does a dark feild microscope work?

Answer 8

light shines on the sample form the side resulting in the slide background being dark.

Question 9

what is the advantage of dark feild microscopy?

Answer 9

the object appears bright on a dark background which provides excellent contrast without the need for a stain

Question 10

What is phase contrast microsopy?

Answer 10

Microscope that amplifies small differences in light phase. when light passes through an object it gets refracted causing the light wavelengths to be out phase.

Question 11

how does Differential Interference Contrast Microscope (DIC) work

Answer 11

use two beams of plane polarized light arranged at right angles to each other. a refence beam passing through an adjacent area of the sample

Question 12

Differential Interference Contrast Microscope (DIC) use what to create a visible image?

Answer 12

refractive indicies and thicknesses of different parts of the specimen

Question 13

How is resolution maximized with Differential Interference Contrast Microscope (DIC)?

Answer 13

by passing the light through prisms

Question 14

how does flourescent microscopes work?

Answer 14

by the objects ability to emit light on its own. normally by injecting florescent dyes or tags.

Question 15

what compounds allow for the ability to emit light?

Answer 15

fluorophores

Question 16

how does a confocal laser microscopy work

Answer 16

A computer guides and collects the image data and combines to create the viewed 3D image. it basically creates a series of flat images of the sample at different levels and stacks them into the final image.

Question 17

what is fixation?

Answer 17

the process of sticking the microorgansim to the slide

Question 18

what are the two methods of fixation?

Answer 18

applying heat to the slide so that the sugars cook on the slide leaving the imprint, using chemicals to immobalize the cell and promote extensive crosslinking between biological molecules and the slide glass

Question 19

what is staining?

Answer 19

the use of dyes based on their charge properties either + or -.

Question 20

what is a differential stain?

Answer 20

the use of more than one stain

Question 21

what is a popular differential stain?

Answer 21

the gram stain which stain differently based on the physiology of their outer surface. it can also be used to determine what medical treatments to use in medical microbiology.

Question 22

what is the difference between gram positive and gram negative

Answer 22

gram positive bacteria have thick walls of peptidoglycan while gram negative bacteria have a thin outer membrane

Question 23

How does a electron microscope work?

Answer 23

beams of electrons are used in place of light beams

Question 24

what are advatages of electron microscopy?

Answer 24

the electrons have shorter wavelengths which allow for much higher resolution

Question 25

how does transmission electron microscopy work?

Answer 25

shoots beams through the sample and the imaged is viewed by blocking electrons.

Question 26

why does staining for electron microscopes use heavy metals?

Answer 26

more efficient at blocking out electrons and can be sprayed onto samples to allow for a shadowing effect to better reveal details.

Question 27

what is a drawback of electron microscopy?

Answer 27

the samples need to be in a vacuum as the electrons don’t travel through air efficiently. the samples also have to be dehydrated, fixed, and sectioned

Question 28

how does scanning electron microscopy work?

Answer 28

detects electrons that bounce off the sample rather than be absorbed. similar to confocal scanning electron microscopy the electron beam scans a focused beam of electron along the sample along the sample allowing the image to be generated.

Question 29

How does scanning probe microscopy work?

Answer 29

a very small probe passes over the hills sand valleys of the specimen. a laser beam that is directed at the cantilever is used to monitor vertical movements. light reflected from the cantilever is detected by the photodiode to generate an image of the sample.

Question 30

what is the common name of the scanning probe microscope?

Answer 30

atomic force microscope

Question 31

Advantages of the scanning probe microscopy over electron microscopy?

Answer 31

does not require dehydration of the sample or use of high vacuum