Microbio Lab 1

Question 1

brightfield microscope

Answer 1

a microscope that allows light rays to pass directly to the eye without being deflected by an intervening opaque plate in the condenser

Question 2

light intensity control

Answer 2

varies the intensity of light

Question 3

neutral density filter

Answer 3

needed to reduce the intensity of light below the lower limit allowed by the voltage control

Question 4

ocular

Answer 4

eyepiece

Question 5

objectives

Answer 5

usually three attached to rotatable nose piece

Question 6

low-power objective

Answer 6

10X

Question 7

high-dry objective

Answer 7

40X

Question 8

oil immersion objective

Answer 8

100X

Question 9

condenser

Answer 9

located under stage; collects and directs light from the lamp to the slide being studied

Question 10

diaphragm

Answer 10

regulates the amount of light that reaches the slide

Question 11

coarse/fine adjustment knobs

Answer 11

bring objects into focus

Question 12

diopter adjustment ring

Answer 12

…

Question 13

resolving power

Answer 13

the ability of the lens to completely separate two objects in a microscopic field

Question 14

numerical aperture

Answer 14

a mathematical expression that describes how the condenser lens concentrates and focuses the light rays from the light source

Question 15

parfocal/parcentral

Answer 15

image will remain both centered and in focus when changing from a lower-power to a higher-power objective lens

Question 16

colony

Answer 16

a visible mass of cells

Question 17

star diaphragm

Answer 17

allows only peripheral light rays to pass up through the condenser; requires maximum illumination

Question 18

cardioid condenser

Answer 18

provides greater light concentration for oblique illumination that the star diaphragm

Question 19

Describe the position of your hands when carrying the microscope to and from your laboratory bench.

Answer 19

The microscope should be carried with two hands-one under the base and the other one on the arm

Question 20

Differentiate between the limit of resolution of the typical light microscope and that of the unaided human eye

Answer 20

The limit of resolution for a light microscope is about 0.2micrometers and 0.2mm for the unaided eye.

Question 21

(a) What two adjustments can be made to the condenser?

Answer 21

(a) The condenser can be moved up or down using the diaphragm.
(b) Adjusting the condenser affects the amount of light that reaches the slide.

Question 22

Why are condenser adjustments generally preferred over the use of the light intensity control?

Answer 22

Keeping the lamp on a lower voltage will increase the lamp life.

Question 23

When using the oil immersion lens, what four procedures can be implemented to achieve the maximum resolution?

Answer 23

To achieve max resolution– (1) apply a drop of immersion oil; (2) place blue filter over light source; (3) open the diaphragm; and (4) keep condenser at the highest position.

Question 24

Why is it advisable to start first with the low-power lens when viewing a slide?

Answer 24

It is best to start with a low power lens to get an overview of the slide and find the object you wish to study.

Question 25

Why is it necessary to use oil in conjunction with the oil immersion lens and not with the other objectives?

Answer 25

Oil is used with oil immersion lens because the small working distance does not allow enough light to enter the lens. The oil, which has the same refractive index as glass, directs more light into the lens (limits the loss of light due to refraction)

Question 26

What is the relationship between the working distance of an objective lens and its magnification power?

Answer 26

As magnification increases, working distance decreases

Question 27

Which objective lens provides the highest magnification?

Answer 27

oil immersion

Question 28

Which objective lens provides the second-highest magnification?

Answer 28

high-dry

Question 29

Which objective lens provides the lowest magnification?

Answer 29

low-power

Question 30

Which objective lens has the shortest working distance?

Answer 30

oil-immersion

Question 31

The coarse focus knob should only be adjusted when using which objective lens?

Answer 31

low-power

Question 32

Which lens collects and focuses light from the lamp onto the specimen on the slide?

Answer 32

condenser

Question 33

Which lens often comes in pairs?

Answer 33

ocular

Question 34

Diopter adjustments can be made to which lens?

Answer 34

ocular

Question 35

A diaphragm is used to regulate light passing through which lens?

Answer 35

condenser

Question 36

The coarse and fine focus knobs adjust the distance between....?

Answer 36

the stage and the objective lens

Question 37

lens

Answer 37

ocular or eye piece (10X)

Question 38

Total magnification

Answer 38

ocular x objective

Question 39

working distance

Answer 39

distance between objective lens and slide; decreases with increasing magnification

Question 40

field of view

Answer 40

area viewed through ocular; decreases with increasing magnification (center specimen before magnification)

Question 41

Colonial morphology

Answer 41

Size: small, medium, large (relative to each other) Color: white, cream, yellow, orange, red, etc. Shape: round, irregular, filamentous Edge: entire, rhizoid, lobate Elevation: flat, convex, umbonate

Question 42

In what ways do the macroscopic features of bacterial colonies differ from those of molds?

Answer 42

Bacterial colonies are generally small and smooth whereas fungal colonies are larger and fuzzy

Question 43

Why is the level of contamination measured as number of colones rather than size of colonies?

Answer 43

Each colony is produced from a single cell so the number of colonies indicate the original level of colonies; colony size represents growth rate

Question 44

Should one be concerned to find bacteria on the skin? How about molds?

Answer 44

Bacteria are a part of normal skin flora but mold are not. Molds are a contaminent picked up from the environment

Question 45

How can microbial levels be controlled?

Answer 45

handwashing; disinfectants; filtration systems