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 eetly affeted Bitish attle, ealy destoyed the Bitish eef idusty, ad 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
deteted i attle ith ad o disease. ‘eetly, the old faous ioiologist D. Noital polaied
that ad o disease oeys Kohs postulates. Is D. Noital oet? 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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