Exam (elaborations)
MBY 161 Possible Exam Questions with Answers 2021/2022
- Course
- MBY 161/Microbiology 161
- Institution
- University Of Pretoria (UP)
MBY 161 Possible Exam Questions with Answers 2021/2022
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Define a microorganism. [1]Organisms that are too small to be seen individually with the unaided eye.
Describe the most important distinguishing characteristics that can be used to
separate bacteria, archaea, fungi, protozoa, algae, and viruses on the basis of
cellular structure.[12]
Bacteria are prokaryotic with peptidoglycan cell walls.
Archaea are prokaryotes lacking peptidoglycan.
Fungi are eukaryotes with chitin cell walls.
Protozoa are unicellular eukaryotes without cell walls.
Algae are unicellular eukaryotes with chloroplasts and cell walls.
Viruses are not composed of cells. They consist of a protein coat enclosing a nucleic acid.
In the 1860’s Joseph Lister observed that patients recovered completely from
simple fractures but that compound fractures had “disastrous consequences”. He
knew that the application of phenol (carbolic acid) to fields in the town of Carlisle
prevented cattle disease and that phenol killed bacteria. Lister treated compound
fractures with phenol, and his patients recovered without complications. How was
Lister influenced by Pasteur’s work? And why was Koch’s work still needed?[3]
Pasteur showed that microbes were omnipresent and were responsible for “diseases” (i.e.
spoilage) of food; Lister reasoned that these microbes might be responsible for diseases of
people. Neither Lister nor Pasteur proved that microbes caused diseases. Koch provided a
repeatable proof to demonstrate that a microbe causes a disease.
What is the difference between spontaneous generation and biogenesis. [2]
Spontaneous generation - the hypothesis that living organisms arise from nonliving matter;
a “vital force” forms life.
Biogenesis - the hypothesis that living organisms arise from preexisting life.
Describe how spontaneous generation was disproved?[4]
Pasteur demonstrated that spontaneous generation could not take place by performing
experiments with broth and swan-necked flasks. Flasks containing nutrient broth were
heated and allowed to cool while curved neck of the flask prevented microbes from
entering flask but let air in. He proved that microbes are present on non-living matter - air,
liquids and solids.
Explain how an accidental discovery by Alexander Fleming contributed to modern
medicine and microbiology[4]
Fleming observed a mold growing on contaminated bacterial culture plates. He noticed
that the mold inhibited growth of the bacteria. The Penicillium fungus made an antibiotic,
penicillin, that killed S. aureus (bacteria).
What is the difference between resolution and total magnification?[2]
Resolution refers to the ability of a microscope to distinguish two points a specified
distance apart.
Total magnification is a measure of the enlarging ability/power of the microscope (objective
lens magnification multiplied by ocular lens magnification).
Why is immersion oil necessary at 100x but not with the lower power objective?[1]
Much of the light is missed because the higher magnification lenses are small, therefore
immersion oil is used with the oil immersion lens to reduce light loss between the slide and
the lens.
, Explain why it is necessary and how to prepare a smear before staining bacterial
cells. [4]
Before viewing the bacterial cells must be fixed to the slide surface otherwise they will be
washed off when stain is added. When the smear is fixed it also preserves various parts of
the cell in it's natural state with minimal distortion.
1 - Spread thin film of material containing microorganisms on surface of slide. This dilutes
the organisms for viewing.
2 -Allow the film (smear) to air dry. Prevents cells in fluid medium form running of slide.
3 - Fix smear by passing through flame (smear side up) or cover slide with methyl alcohol
for 1 min. This fixes the cells onto the slide as well as preserves various parts of the cell
with minimal distortion.
During a Gram‐stain on a bacterial culture, the student forgets to add the safranin in
the last step. What would the student observe under the microscope? Explain how
the results would be interpreted.[2]
The counterstain safranin can be omitted. Gram-positive bacteria will appear purple, and
gram-negative bacteria will be colourless.
Using a good compound light microscope with a resolving power of 0.3μm, a 40x
ocular lens and a 100x oil immersion lens, would you be able to discern two objects
separated by 3μm? 0.3μm? 300nm? Explain your answer.[2]
You would be able to discern two objects separated by the three distances given because
each is equal to or greater than the resolving power of the microscope.
What is the difference between the term bacillus and Bacillus?[2]
Bacillus without italics describes a cell shape
Bacillus is a genus of bacteria..
Explain the difference between a capsule and a slime layer. [2]
A capsule and slime layer are both a viscous gelatinous polymer that is external to the cell
wall and composed of either polysaccharide, polypeptide or both. In the case of a capsule
this substance if organised and firmly attached to the cell wall, while a slime layer is
unorganised and loosely attached to the cell wall.
What is the importance of the differences between prokaryotic and eukaryotic
ribosomes with regard to antibiotic therapy? [2]
Antibiotics that specifically target the 70S ribosomes will have little effect on human
ribosomes as eukaryotic ribosomes are 80S ribosomes.
How can the Gram reaction be useful in prescribing antibiotic treatment?[1]
Gram‐positive bacteria are not necessarily susceptible to the same antibiotics as gram-
negative bacteria.
What are the major structural differences between Gram-positive and Gram-negative
cell walls?[4]
Gram-negative cell walls have a phospholipid outer membrane (LPS layer), they have a
thin single layered peptidoglycan layer and have a periplasmic space. Gram negative cells
lack teichoic acids and also have 4 rings in their basal bodies. Gram-positive cell walls
have a thick peptidoglycan layer that is multilayered, they lack a periplasmic space, no
outer membrane and have teichoic acids. They also have 2 rings in the basal body.
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