(6)

Question 1

a contrast with the background of the microscope field

Answer 1

contrast

Question 2

the shape of an organism; determining cell morphology is an important first step in identifying a bacterial species

Answer 2

morphology

Question 3

spherical cell

Answer 3

cocci (coccus)

Question 4

rod-shaped cell

Answer 4

bacilli (bacillus)

Question 5

spiral-shaped cell

Answer 5

spirilla (spirillum)

Question 6

slightly curved rods

Answer 6

vibrios

Question 7

short rods

Answer 7

coccobacillus

Question 8

flexible spirals; flexible, curved rods

Answer 8

spirochetes

Question 9

where a variety of cell shapes-slender, ellipsoidal, or ovoid rods- may be seen in a given sample

Answer 9

pleomorphism

Question 10

formed if the two daughter cells remain attached after a coccus divides; have a single division plane and the cells generally occur in pairs

Answer 10

diplococcus

Question 11

formed if the two daughter cells remain attached after a coccus divides

Answer 11

diplobacilli

Question 12

an arrangement resulting from cells that continue to divide in the same plane and remain attached; single division plane, but the cells remain attached to form chains of variable length

Answer 12

streptococcus

Question 13

an arrangement resulting from cells that continue to divide in the same plane and remain attached

Answer 13

streptobacilli

Question 14

a cluster of cells is produced to form a staphylococcus if the division planes of a coccus are irregular; divide in more than three planes to produce a characteristic grape-like cluster of cells

Answer 14

staphylococcus

Question 15

a colored molecule (often a benzene derivative)

Answer 15

chromogen

Question 16

the charged region of a dye molecule that gives it its color; the portion of the chromogen that gives it its color

Answer 16

chromophore

Question 17

the charged portion of a chromogen and allows it to act as a dye through ionic or covalent bonds between the chromogen and the cell

Answer 17

auxochrome

Question 18

staining solution with a negatively charged chromophore

Answer 18

acidic stains

Question 19

staining solution with a positively charged chromophore; where the auxochrome becomes positively charged as a result of picking up a hydrogen ion or losing a hydroxide ion; attracted to the negative charges on the surface of most bacterial cells

Answer 19

basic stains

Question 20

kills the bacteria, makes them adhere to the slide, and coagulates cytoplasmic proteins to make them more visible.

Answer 20

heat-fixed emulsion

Question 21

How does a basic stain work?

Answer 21

The auxochrome becomes positively charged as a result of picking up a hydrogen ion or losing a hydroxide ion. They are attracted to the negative changes on the surface of most bacterial cells. Thus, the cell becomes colored.

Question 22

List 3 common basic stains.

Answer 22

Methylene blue, crystal violet and safranin

Question 23

Why must a sample be heat-fixed?

Answer 23

To kill the bacteria, make them adhere to the slide, and coagulate cytoplasmic proteins to make them more visible.

Question 24

What is the chemical property of the chromogen (dye) used in a negative stain?

Answer 24

The chromogen is acidic and carries a negative charge. (An acidic chromogen gives up a hydrogen ion, which leaves it with a negative charge).

Question 25

Explain why only the background is stained when performing a negative stain.

Answer 25

The negative charge on the bacterial surface repels the negatively charged chromogen, so the cell remains unstained against a colored background.

Question 26

What stain was used in the negative stain procedure performed in class?

Answer 26

Nigrosin or eosin stain

Question 27

What color was the cell after negative staining?

Answer 27

Unstained