Microbio Lab 2

Question 1

phase-contrast microscope

Answer 1

a microscope that is able to differentiate the transparent protoplasmic structures and enhance the contrast between a cell and its surroundings, without the necessity of staining; good for viewing live cells and motility

Question 2

phase shift

Answer 2

as light passes through transparent objects and is slowed down by 1/4 wavelength

Question 3

direct rays

Answer 3

rays that pass straight through unaffected by medium

Question 4

diffracted rays

Answer 4

rays that are bent because they are retarded by the medium (due to density differences)

Question 5

coincidence

Answer 5

if direct and diffracted light waves are brought into exact phase with each other; increased brightness

Question 6

interference

Answer 6

if two light waves of equal amplitude are in reverse phase (1/2 off) and their amplitudes cancel each other to produce a dark object

Question 7

annular stop

Answer 7

structure in diaphragm that allows only a hollow cone of light rays to pass through the condenser to the specimen on the slide

Question 8

bright-phase microscopy

Answer 8

brighter image (amplitude summation)

Question 9

dark-phase microscopy

Answer 9

darker image (amplitude interference or reverse phase)

Question 10

ocular micrometer

Answer 10

…

Question 11

stage micrometer

Answer 11

…

Question 12

aseptic technique

Answer 12

ensures that no contaminating organisms are introduced into culture materials during handling or inoculation; also ensures that the organisms that are being handled do not contaminate the handler or others who may be present; its use means that no contamination remains are you have worked with cultures

Question 13

Staining of cells is often performed to enhance images acquired by brightfield microscopy. Phase-contrast microscopy does not require cell staining. Why is this advantageous?

Answer 13

The movement of the cells and their activities cannot be viewed if the cells are stained since cell staining results in cell death.

Question 14

As ligh passes through a transparent object, how are direct and diffracted light rays produced? How much phase shift occurs?

Answer 14

• Direct rays-unaffected with No phase shift

- Diffracted rays- bend and have a phase shift of 1/4 wavelength.

Question 15

How do coincidence and interference of light rays differ? Which type of image does each produce?

Answer 15

Coincidence- Produces a brighter image

Interference- Produces a darker image

Question 16

Differentiate between bright-phase and dark-phase microscopy in terms of phase shift.

Answer 16

Bright phase-a brighter image (amplitude summation)

Dark phase- a darker image (amplitude interference)

Question 17

Which two items can be used to check the alignment of the annulus and phase ring?

Answer 17

centering telescope and Optovar.

Question 18

A phase-contrast microscope differs from a brightfield microscope by having a _

Answer 18

• Diaphragm with an annular stop

- Phase plate in the objective lens

Question 19

What would be best observed or a bacterial cell using phase-contrast microscopy?

Answer 19

A motility of cells

Question 20

Amplitude summation occurs in phase-contrast optics when both direct and diffracted rays are _

Answer 20

in phase

Question 21

The phase-contrast microscope is best suited for observing _

Answer 21

Living organisms on a slide with a cover glass

Question 22

Where should a label be written on an agar plate?

Answer 22

on the bottom

Question 23

How should agar plates be incubated

Answer 23

Upside down to prevent condensation on the agar

Question 24

Disinfectants are effective against which types of organisms?

Answer 24

Disinfectants are effective against vegetative cells and viruses but not endospores

Question 25

Compare/contrast the growth of bacteria in different physical media (broths, slants, and agar plates)? What are the advantages and disadvantages of each?

Answer 25

Some bacteria could grow better in broth vs plate or vice versa