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SLE234- Midterm Exam Guide - Comprehensive Notes for the exam ( 47 pages long!)


Department
Science, Engineering and Built Environment
Course Code
SLE234
Professor
Cenk
Study Guide
Midterm

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Deakin
SLE234
MIDTERM EXAM
STUDY GUIDE

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MICROBIOLOGICAL SEMINARS
SEMINAR 1 (15th APRIL)
1. ln an early experiment testing the hypothesis of spontaneous generation, Francesco Redi placed raw meat in
beakers, covered some of the beakers with a fine cloth, and left the remaining beakers open. Maggots
appeared in the open beakers but not the covered beakers. However, the meat in the covered beakers
eventually did spoil. Suggest three possible sources of the organisms that spoiled the meat. Given current day
knowledge, suggest three procedures to help prevent spoilage that Redi could have incorporated as part of his
experiment (only procedures that could have been done in 1688)
a. Contamination of beakers, organisms on hands, meat, cloth or in air
b. Salting, heating the beaker (sterilization), and boiling the jar with the meat in it (like jam).
2. Mad o disease eetly affeted Bitish attle, ealy destoyed the Bitish eef idusty, ad is still a ajo
concern. Analysis of the dead cattle revealed tissue degradation in the brain (accounting for the erratic
behaviour of diseased animals), but no foreign prokaryotic or non-cow eukaryotic DNA or RNA was ever
deteted i attle ith ad o disease. ‘eetly, the old faous ioiologist D. Noital polaied
that ad o disease oeys Kohs postulates. Is D. Noital oet? Why o hy ot?
a. Incorrect. Lack of nucleic aid indicated no organisms is present. Therefore cannot be isolated, grown
in pure culture, infected into healthy host and recovered unchanged. (kohs postulates)
3. Despite the fact that there are many more people inhabiting the planet now than 500 to 1,000 years ago, there
are many fewer epidemics today involving disease-causing bacteria. Suggest at least three reasons for the
higher incidence of disease in the past.
a. Lack of hygiene, antibiotics, education, vaccines/ medicine, living conditions.
4. Dr. Noital performs the following experiment to determine whether a special quality of air allows spontaneous
generation to occur. 1. Boiled beef broth is placed in two sterile flasks, flask A and flask B. 2. Untreated air is
circulated through flask A. 3. Air treated with gamma radiation (dose sufficient to kill bacteria) is circulated
through Flask B. 4. Both flasks are incubated at room temperature. l Growth of organisms occurs in flask A but
not flask B. Dr. Noital reasons that organisms in the air contaminated the broth in flask A. He also reasons that
the gamma radiation treatment killed the organisms in the air circulated in flask B. He concludes that growth of
organisms was due to contamination, not spontaneous generation. He also concludes that there is no special
quality of air that allows spontaneous generation to occur. Are Dr. Noital's reasoning and conclusions correct?
Why or why not?
a. Incorrect. Could be argued that treatment with gamma radiation altered some quality of air
necessary for spontaneous generation. Needs control where is filtered but otherwise untreated
before going through the flask.
5. If most bacteria have a diameter of 0.5 to 1.0 µm, what would this range be in nanometers? In Angstroms?
a. 500-100nm 5000-10000ang
6. An average bacterium is 2.5 µm in length. The human eye cannot see an object smaller than 0.1 mm. How
much larger than the average bacterium is the smallest object that the human eye can see?
a. 0.1mm=100um therefore 40x greater than 2.5um
7. How could you obtain 2,000x magnification with a 100x objective? Would it be worthwhile to upgrade the
microscope from 1,000x to 2,000x at a considerable cost? (Hint: the smallest bacterium that it is usually useful
to see is 0.5 to 1.0 µm thick).
a. Ocular x objective = magnification. Use 20x optical lens. Missing something unable to resolve with
2000x magnification, also not necessary since can use 1000x magnification to see most bacteria.
0.5um x 10000= 0.5 mm, 5x larger than smallest object eye can see unaided.
8. Why do you think that the refractive index of air is less than the refractive index of glass, i.e., what property of
air and glass might be responsible for refractive index?
a. Change of speed (refraction) is due to interaction of polarisable electrons in molecules in glass.
Higher atomic density of glass responsible for difference.
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9. The bacterium Twodimentia flaticus is a highly unusual, and extremely rare, rectangular-shaped bacterium
(existing only in the imagination of individuals suffering from the stress of creating microbiology problems). The
sides of this rectangular cell are 10 microns and 4 microns in length. However, the bacterium is only 0.1 micron
thick. You examine T. Flaticus using a light microscope. You are surprised when you see rectangles that are 10 x
4 microns in size (side view), but not any that are 0.1 x 10 microns or 0.1 x 4 microns in size (end-on view).
Should you have been surprised? Why or why not?
a. 0.17 is the lowest level of resolution of a light microscope. Cannot cleary resolve ojects less that
0.17 missing
10. A nerve impluse is transmitted to your brain when light strikes the cells in your retina. Impulses sent by a
number of cells are assembled in your brain to create the image. In other words, an image is formed in your
brain when light reflected from an object strikes a number of retinal cells. On this basis, explain why the
unaided eye cannot see a bacterium. If you had godlike powers, what change could you make in the retina that
might allow an otherwise unaided eye to see a bacterium?
a. Image falls between retinal cells because they are too small decrease size and increase density of
retinal cells so that mage of bacteria covers many cells.
11. Using an appropriate lens and oil immersion, what would be the maximum resolution (in microns) of a
microscope that could use a wavelength of 100 nm (assume that such a device exists)?
a. 100nm = 0.1um (0.1um x 0.5)/ 1.5 (numerical aperture)= 0.033um
12. Using a light microscope and the oil immersion technique, Dr. Noital sees a coccal type bacterium that has a
diameter of 0.244 microns. Calculate the wavelength of light in nanometers that was produced by the light
source. Is this the maximum resolution achievable for the light microscope? Why or why not?
a. (0.244/0.5) x 1.5 = 0.732um = 732 nm
b. No could just use 500nm to gain a better resolution.
13. If you had appropriate lenses and oil immersion, what would be the maximum resolution (in microns) of a
microscope that could use a wavelength of 250 nm?
a. (0.5 x 0.250) / 1.5 = 0.083um
14. Will a coccus type bacterium with a radius of 1 um (bacterium A) have more efficient uptake of nutrients than
a coccus type bacterium with a radius of 0.1um (bacterium B)? If so, why? If not, why? Explain reference to the
surface to volume ratios of the bacteria. How much more efficient (by what factor) will
a. Uptake is related to surface to volume ration. The larger the ratio, the more efficient the uptake.
Missing
15. The surface to volume ratio of a
a. 3/r, r=3. Missing
SEMINAR 2 (22ND APRIL)
1. You wish to visualise the region of Escherichia coli (a common intestinal bacterium, widely used in laboratory
studies) that contains DNA. However, your culture of E. coli is contaminated with Bacillus problematicus, and
both types of bacterium are rod-shaped and about the same size. In short, they look exactly the same under
the light iosope. You eee that E. oli is Ga egatie, ad fo Begeys aual you lea that
B. problematicus is Gram positive. You also recall that the first stain used in the Gram test, crystal violet, is a
cationic stain (i.e., positively charged) and that DNA, being a nucleic acid, is negatively charged. Thus, you
decide to simultaneously stain for DNA and distinguish the two bacteria visually by doing a Gram test. Your
rationale is that in the first stage of the Gram test, the crystal violet will stain the DNA, and then the second
stage of the Gram test will differentially stain the two bacteria, allowing you to specifically visualise the DNA
region of E. coli. Unfortunately, your reasoning is faulty and your plan will not work. Give two reasons why it
will fail.
a.
2. Will a coccus type bacterium with a radius of 1 um (bacterium A) have more efficient uptake of nutrients
than a coccus type bacterium with a radius of 0.1 um (bacterium B)? If so, why? If not, why not? Explain with
reference to the surface to volume ratios of the bacteria. How much more efficient (by what factor) will
nutrient uptake be in the bacterium that has the most efficient uptake?
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