Biol 240L Lab Final Exam ACTUAL
QUESTIONS AND CORRECT ANSWERS
What are simple stains used for? - CORRECT ANSWERS✅✅Determining the size, shape
and arrangement of bacterial cells
How do positive staining procedures work? - CORRECT ANSWERS✅✅The stain has a
positively charged chromophore, so the negatively charged bacterial outer surface will be
attracted to the chromophores to stain the organism
Why are slides heat fixed prior to staining? - CORRECT ANSWERS✅✅1.) Kill Bacteria
2.) Adherence to slide
3.) Sample will more readily take up stains
What are some simple dyes used for simple staining procedures? - CORRECT
ANSWERS✅✅-methylene blue
- basic fuchsin
- crystal violet
What are the shapes of E. coli and Bs. Bacilli? - CORRECT ANSWERS✅✅coccus and rod
shapes, respectively
How do you calculate the magnification of specimens under a microscope? - CORRECT
ANSWERS✅✅size of specimen (in μm) / actual size of image (in μm)
What type of staining technique is the gram stain? - CORRECT ANSWERS✅✅differential
stain
Gram-positive bacteria - CORRECT ANSWERS✅✅- bacteria that do not have an outer
membrane
- will stain purple during the gram stain procedure
, What are Gram-negative bacteria, and how do they appear during the Gram-stain procedure?
- CORRECT ANSWERS✅✅- bacteria that have an outer membrane
- will stain red during the gram stain procedure
mordant; what is an example of a mordant in the gram stain procedure? - CORRECT
ANSWERS✅✅A substance added to a staining solution to make it stain more intensely;
iodine
decolorizing agent - CORRECT ANSWERS✅✅a solution used in the process of removing a
stain
Why do gram positive bacteria stain purple? - CORRECT ANSWERS✅✅they are stained
by the crystal violet stain, and will hold the stain in their membrane so it cannot be removed
by a decolorizing agent and will then not be stained by the counter staining dye.
Why do gram negative bacteria stain red? - CORRECT ANSWERS✅✅they do not readily
hold the crystal violet dye in their membrane, so the dye will be removed by the decolorizing
agent and they will be stained by the counter stain.
What factors affect a bacterium's reaction to the Gram stain? - CORRECT ANSWERS✅✅-
culture age
- pH of the medium
Under what conditions may a gram-positive bacterial culture stain as if they are gram-
negative, and why? - CORRECT ANSWERS✅✅Older cultures and those grown in acidic
mediums stain as gram-negative cultures because their cell walls have been degraded.
Are E. coli and S. epidermis gram positive or gram negative? - CORRECT ANSWERS✅✅-
E. coli: gram-negative
- S. epidermis: gram positive
What important bacterial cultures were used to test the Kinyoun method, and what were the
results? - CORRECT ANSWERS✅✅- Mycobacterium phlei: is an acid-fast bacterial culture
- Bacillus megabacterium: is not an acid-fast bacterial culture
QUESTIONS AND CORRECT ANSWERS
What are simple stains used for? - CORRECT ANSWERS✅✅Determining the size, shape
and arrangement of bacterial cells
How do positive staining procedures work? - CORRECT ANSWERS✅✅The stain has a
positively charged chromophore, so the negatively charged bacterial outer surface will be
attracted to the chromophores to stain the organism
Why are slides heat fixed prior to staining? - CORRECT ANSWERS✅✅1.) Kill Bacteria
2.) Adherence to slide
3.) Sample will more readily take up stains
What are some simple dyes used for simple staining procedures? - CORRECT
ANSWERS✅✅-methylene blue
- basic fuchsin
- crystal violet
What are the shapes of E. coli and Bs. Bacilli? - CORRECT ANSWERS✅✅coccus and rod
shapes, respectively
How do you calculate the magnification of specimens under a microscope? - CORRECT
ANSWERS✅✅size of specimen (in μm) / actual size of image (in μm)
What type of staining technique is the gram stain? - CORRECT ANSWERS✅✅differential
stain
Gram-positive bacteria - CORRECT ANSWERS✅✅- bacteria that do not have an outer
membrane
- will stain purple during the gram stain procedure
, What are Gram-negative bacteria, and how do they appear during the Gram-stain procedure?
- CORRECT ANSWERS✅✅- bacteria that have an outer membrane
- will stain red during the gram stain procedure
mordant; what is an example of a mordant in the gram stain procedure? - CORRECT
ANSWERS✅✅A substance added to a staining solution to make it stain more intensely;
iodine
decolorizing agent - CORRECT ANSWERS✅✅a solution used in the process of removing a
stain
Why do gram positive bacteria stain purple? - CORRECT ANSWERS✅✅they are stained
by the crystal violet stain, and will hold the stain in their membrane so it cannot be removed
by a decolorizing agent and will then not be stained by the counter staining dye.
Why do gram negative bacteria stain red? - CORRECT ANSWERS✅✅they do not readily
hold the crystal violet dye in their membrane, so the dye will be removed by the decolorizing
agent and they will be stained by the counter stain.
What factors affect a bacterium's reaction to the Gram stain? - CORRECT ANSWERS✅✅-
culture age
- pH of the medium
Under what conditions may a gram-positive bacterial culture stain as if they are gram-
negative, and why? - CORRECT ANSWERS✅✅Older cultures and those grown in acidic
mediums stain as gram-negative cultures because their cell walls have been degraded.
Are E. coli and S. epidermis gram positive or gram negative? - CORRECT ANSWERS✅✅-
E. coli: gram-negative
- S. epidermis: gram positive
What important bacterial cultures were used to test the Kinyoun method, and what were the
results? - CORRECT ANSWERS✅✅- Mycobacterium phlei: is an acid-fast bacterial culture
- Bacillus megabacterium: is not an acid-fast bacterial culture
