Microbiology Lab Midterm Dave Bachoon Exam
Questions and Answers
What types of microbes dominate thee air of your microbiology lab? - -Bacteria, fungi, and
viruses
-Why is it important to use aseptic technique when inoculating tubes and media plates? - -
to prevent unwanted organisms (contaminants) from getting in or on experimental tubes
or plates.
-How does the procedure for using the microscope differ using high dry power as opposed
to low power? - -high power is used for smaller objects and uses fine focus lens, low power
is used for larger objects and uses coarse focus lens
-How does loss of light affect the resolution of a specimen? - -decreases the resolution or
clarity
-What is the purpose of using immersion oil? - -refraction of light is minimized and
increases the resolution
-What two things can be adjusted to control the amount of light passing into a specimen? -
-Iris diaphram and light intensity adjuster
-Describe how to properly care for a microscope after immersion oil has been used? - -
Remove immersion oil by using a drop of isopropanol (70%) on lens paper
-Why must we stain bacteria before examining them with a microscope? - -Because most
bacteria lack natural pigmentation, cells are hard to visualize with out first applying a stain
-What component of a stain gives bacteria their color? - -chromophore group
-What advantage does knowing the morphology and arrangement of a culture provide? - -
Each bacterium is best treated with a different antibiotic which is based on the morphology
and arrangement
-Why must you use water when preparing a smear from a solid culture? - -water helps to
spread the culture over the glass and produces an even and more dilute density
-What is a differential stain? - -The use of two or more dyes that react differently with
different kinds/parts of bacteria.
-How can the age of the cell culture affect the results of a gram stain? - -Older cultures
begin to loose the ability to retain the primary dye. Aging of the cells tends to make them
become Gram Neg. even though they are not
, -Which is the most critical step in the gram staining procedure? - -Decolorization- If you
decolorize too vigorously all cells will loose the primary stain and will appear Gram Neg.
-Can a bacteria cell produce more than one spore? - -No, a cell must lyse in order to
produce an endospore
-Why is heat required to stain endospores? - -heat is required because you have to
penetrate the cell wall
-What is the advantage to the bacteria to produce endospores? - -They are resistant to
physical agents (freezing temp., heat, and desiccation) and chemical agents
(antibiotics/bacterides)
-Can bacteria survive with a capsule? - -Yes
-What are the advantages of a capsule to bacteria cells? - -provides protection and helps
with resistance
-After performing the acid-fast stain, what is the color of the cells lacking mycolic acid? - -
blue
-How does a layer of mycolic acid contribute to these bacteria ability to cause disease? - -
Resists drying and environmental stress so bacterial can survive harsh conditions. They
aren't digested by phagocytes
-Acid-fast stain cells are - -Red
-When performing a streak plate why is it necessary to flame the loop between each streak
pattern? - -So that you drag less and less bacteria with you, spreading out the colonies
-How can you confirm that your isolated colony came from a single type of bacteria cell? - -
by looking at the color and morphology under a microscope or by growing that colony on a
new plate
-If you were asked to isolate bacteria from a water sample which of these isolation
techniques would you use and why? - -Streak plate method to isolate microorganisms
-When performing the spread plate technique why is it important to burn off all the the
alcohol from the glass rod before attempting to spread the bacteria on the plate? - -
sterilizes the rod at cooler temperature and also reduces the chances of burning your
fingers
-What is a complex media? - -contains some ingredients of unknown
composition/concentration (soup)
Questions and Answers
What types of microbes dominate thee air of your microbiology lab? - -Bacteria, fungi, and
viruses
-Why is it important to use aseptic technique when inoculating tubes and media plates? - -
to prevent unwanted organisms (contaminants) from getting in or on experimental tubes
or plates.
-How does the procedure for using the microscope differ using high dry power as opposed
to low power? - -high power is used for smaller objects and uses fine focus lens, low power
is used for larger objects and uses coarse focus lens
-How does loss of light affect the resolution of a specimen? - -decreases the resolution or
clarity
-What is the purpose of using immersion oil? - -refraction of light is minimized and
increases the resolution
-What two things can be adjusted to control the amount of light passing into a specimen? -
-Iris diaphram and light intensity adjuster
-Describe how to properly care for a microscope after immersion oil has been used? - -
Remove immersion oil by using a drop of isopropanol (70%) on lens paper
-Why must we stain bacteria before examining them with a microscope? - -Because most
bacteria lack natural pigmentation, cells are hard to visualize with out first applying a stain
-What component of a stain gives bacteria their color? - -chromophore group
-What advantage does knowing the morphology and arrangement of a culture provide? - -
Each bacterium is best treated with a different antibiotic which is based on the morphology
and arrangement
-Why must you use water when preparing a smear from a solid culture? - -water helps to
spread the culture over the glass and produces an even and more dilute density
-What is a differential stain? - -The use of two or more dyes that react differently with
different kinds/parts of bacteria.
-How can the age of the cell culture affect the results of a gram stain? - -Older cultures
begin to loose the ability to retain the primary dye. Aging of the cells tends to make them
become Gram Neg. even though they are not
, -Which is the most critical step in the gram staining procedure? - -Decolorization- If you
decolorize too vigorously all cells will loose the primary stain and will appear Gram Neg.
-Can a bacteria cell produce more than one spore? - -No, a cell must lyse in order to
produce an endospore
-Why is heat required to stain endospores? - -heat is required because you have to
penetrate the cell wall
-What is the advantage to the bacteria to produce endospores? - -They are resistant to
physical agents (freezing temp., heat, and desiccation) and chemical agents
(antibiotics/bacterides)
-Can bacteria survive with a capsule? - -Yes
-What are the advantages of a capsule to bacteria cells? - -provides protection and helps
with resistance
-After performing the acid-fast stain, what is the color of the cells lacking mycolic acid? - -
blue
-How does a layer of mycolic acid contribute to these bacteria ability to cause disease? - -
Resists drying and environmental stress so bacterial can survive harsh conditions. They
aren't digested by phagocytes
-Acid-fast stain cells are - -Red
-When performing a streak plate why is it necessary to flame the loop between each streak
pattern? - -So that you drag less and less bacteria with you, spreading out the colonies
-How can you confirm that your isolated colony came from a single type of bacteria cell? - -
by looking at the color and morphology under a microscope or by growing that colony on a
new plate
-If you were asked to isolate bacteria from a water sample which of these isolation
techniques would you use and why? - -Streak plate method to isolate microorganisms
-When performing the spread plate technique why is it important to burn off all the the
alcohol from the glass rod before attempting to spread the bacteria on the plate? - -
sterilizes the rod at cooler temperature and also reduces the chances of burning your
fingers
-What is a complex media? - -contains some ingredients of unknown
composition/concentration (soup)
