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BIO 390 Lab Exam
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Exam of 19 pages for the course BCH 462 Urea Cycle, Fatty Acid Synthesis at BCH 462 Urea Cycle, Fatty Acid Synthesis (BIO 390 Lab Exam)
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BIO 390 Lab ExamWhat is the primary use of slants? - CORRECT ANSWER-To provide a solid
growth surface that is easier to store/transport.
What is the primary use of deeps? - CORRECT ANSWER-To allow anaerobic
bacteria to grow.
What is the primary use of broths? - CORRECT ANSWER-To grow large
numbers of bacteria in a small space.
Can we determine whether a broth culture is pure by visually inspecting it without
a microscope? - CORRECT ANSWER-No
Can we determine whether a deep culture is pure by visually inspecting it without
a microscope? - CORRECT ANSWER-No
Can we determine whether a slant culture is pure by visually inspecting it without
a microscope? - CORRECT ANSWER-No
When is a loop preferable for transferring bacteria? - CORRECT ANSWER-A
loop is preferable when transferring cultures to a slant or a broth.
When is a needle preferable for transferring bacteria? - CORRECT ANSWER-A
needle is preferable when making deep cultures.
What is the purpose of flaming the loop before use? - CORRECT ANSWER-To
sterilize the loop from environmental microbes.
What is the purpose of flaming the loop after use? - CORRECT ANSWER-To
sterilize the loop from cultured microbes.
Why must the loop be cool before you touch it to a culture? - CORRECT
ANSWER-A hot loop would heat up the bacteria enough to denature and kill the
microbes.
,Should you set the loop down to let it cool? - CORRECT ANSWER-You should
not set the loop down to cool because that would contaminate it.
Why is aseptic technique important? - CORRECT ANSWER-Minimizes
contamination and cross-contamination.
What evolutionary advantage would there be to the formation of a pellicle in a
liquid medium by a bacterium? - CORRECT ANSWER-It would provide
oxygen-loving bacteria with the ability to float on the surface of the liquid and
form aerobic colonies.
How can you tell that the media provided for this exercise were sterile? -
CORRECT ANSWER-There was no growth prior to the transfer of bacteria. The
broth was clear and not turbid.
Why is it desirable that microscope objectives be parfocal? - CORRECT
ANSWER-Because parfocal microscope objectives remain focused when
magnification is changed, so you can change lenses without losing focus.
Which objective focuses closest to the slide? - CORRECT ANSWER-100x oil
immersion
What controls the amount of light reaching the ocular lens? - CORRECT
ANSWER-Iris diaphragm
What effect does increased magnification have on the field of view? - CORRECT
ANSWER-As the magnification increases, the field of view decreases.
Name two ways in which you can enhance the resolving power. - CORRECT
ANSWER-1.) Use a shorter wavelength of light
2.) Increase numerical aperture
What advantage does the low-power objective lens have over the immersion
objective for viewing fungi? - CORRECT ANSWER-It provides a better view of
the overall shape since fungi are significantly larger than bacteria.
, What would occur if water were accidentally used water in place of immersion
oil? - CORRECT ANSWER-The image would not be clear because the
immersion oil helps bend the light to focus correctly.
Of what value is a simple stain? - CORRECT ANSWER-A simple stain allows
you to see the size, morphology, and arrangement of the cells.
What is the purpose of fixing the smear? - CORRECT ANSWER-To prevent the
sample from being lost during staining.
In heat fixing, what would happen if too much heat were applied? - CORRECT
ANSWER-The cells could be denatured and may lose their structural integrity,
which would make them less viewable under the microscope. The glass slide
could crack or melt with enough heat.
Methylene blue can be prepared as a basic stain or an acidic stain. How would
the pH effect the staining of bacteria. - CORRECT ANSWER-The bacteria can
only be stained by a dye with a charge opposite their own. An acidic dye's
negative charge would be repelled by the negative charges of the bacterial cell.
Can dyes other than methylene blue be used for direct staining? - CORRECT
ANSWER-Yes, any dye that can be prepared as a basic stain could be used
because the stain can permeate the cell wall and adhere by weak ionic bonds to
the negative charges of the bacterial cell.
Bacteria can be seen without staining. Why then was Koch's recommendation for
fixing and staining important for microbiology? - CORRECT ANSWER-Fixing kills
the bacteria without distorting their shape. This allows us to see structure and
later allowed us to see things like gram stain.
What types of dyes are used for negative staining? - CORRECT ANSWER-Dyes
with a negative charge, because they are repelled by the negative cell wall and
dye the background instead of the cells.
What microscopic technique gives a field similar in appearance to that seen in
the negative stain? - CORRECT ANSWER-Dark field microscopy
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