Blog

Word recognition testing is typically conducted at ____________ dB above SRT

Which tuning-fork test compares air and bone conduction within the same ear?

You conduct an Ames test on a chemical you suspect might be a carcinogen. Following incubation, you count 3 colonies on your control plate (no chemical added) and over 400 colonies on your experimental plate (chemical added). From this information, you can conclude ______.

You use replica plating to isolate a culture of an E. coli auxotroph, unable to grow without tryptophan, from a culture of prototrophs. For a number of months, you propagate your tryptophan auxotroph culture on GSA (glucose salts agar) medium supplemented with tryptophan. One day, you mistakenly transfer some of your strain onto a new GSA plate that does not contain tryptophan. You realize your mistake after you have left the lab for the day and it is too late to correct it. However, when you return following 24 hours of incubation, you discover a few colonies of E. coli growing on the GSA medium. Please explain this result: why were you able to originally obtain a tryptophan auxotroph from a prototroph culture, and why months later did you find E. coli growth on GSA lacking tryptophan?

Consider the cyanobacteria Nostoc. Individual cells grow attached to each other in long chains produced from binary fission with cells remaining attached (e.g., streptococcus). Most perform photosynthesis, using photosystems I and II to generate ATP and NADPH that they use to power the fixation of carbon dioxide via the Calvin cycle. However, a small number form heterocysts, cells that instead of performing photosynthesis, fix nitrogen into ammonium. Heterocysts share their nitrogen compounds with their photosynthetic neighbors, who in turn share sugars with the heterocysts. If you extracted and analyzed all the mRNA from a single heterocyst and all the mRNA from a single photosynthetic cell and compared both sets of mRNA, would you find mRNA that is different between these two cell types, photosynthetic and nitrogen fixing heterocyst? If so, what would it represent?

You plate out a liquid culture of E. coli on TSA containing the antibiotic streptomycin, incubate for 24 hours, and observe a single colony. From this you obtain a pure culture of streptomycin resistant E. coli, which you propagate on TSA with streptomycin in the following weeks. You then inoculate your culture onto TSA without streptomycin and continue propagating it over the coming months on TSA lacking the antibiotic. Months later, you discover your E. coli strain is no longer resistant to streptomycin. Please explain this result: why was your original colony resistant to streptomycin, and why, months later, did you end up with a culture that was not resistant to the antibiotic?

Consider the cyanobacteria Anabaena. Individual cells grow attached to each other in long chains produced from binary fission. Most perform photosynthesis, using photosystems I and II to generate ATP and NADPH that they use to power the fixation of carbon dioxide via the Calvin cycle. However, a small number form heterocysts, cells that fix nitrogen into ammonium instead of performing photosynthesis. Heterocysts share their nitrogen compounds with their photosynthetic neighbors, who in turn share sugars with the heterocysts. If you extracted all the mRNA from a single heterocyst, and all the mRNA from a single photosynthetic cell, what information would this give you, i.e., what would this tell you about them?

Which part of the audiometer controls the frequency of tones?

Streptomyces rishiriensis is a Gram positive bacterium that produces dark melanin pigments and a number of antimicrobial compounds. You hope to find gene(s) responsible for the production of these melanin pigments. You transform a culture with a plasmid containing a transposon and a kanamycin resistance gene (kanR). Considering your transformation efficiency will be low, how might you find bacteria that have been successfully transformed?

Streptomyces rishiriensis is a Gram positive bacterium that produces dark melanin pigments and a number of antimicrobial compounds. You hope to find gene(s) responsible for the production of these melanin pigments. You transform a culture with a plasmid containing a transposon and a kanamycin resistance gene (kanR) and successfully isolate transformed mutants. You grow them in culture and spread them on the surface of multiple TSA plates. Following incubation, you observe mostly dark colonies along with an occasional clearish/white colony. What might best explain the presence of these clearish/white colonies?