It is estimated that the mass of bacteria and fungi in the top six inches of an acre of soil is
A. 2 tons.
B. 100 lb.
C. 10 tons.
D. 500 lb.
A. 2 tons.
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The mechanism of phase variation in Salmonella typhimurium:
A. uses site-specific recombination to invert the fljA and fljB genes so they now are not contiguous with their promoter. Expression of these genes is now prevented. B. uses site-specific recombination to invert the fljA and fljB promoter, preventing transcription of the two genes. Without repressor the fljC protein is now expressed. C. uses site-specific recombination to delete the repressor, fljA. Without repressor the fljC protein is now expressed. D. uses site-specific recombination to delete the fljB gene so only fljC can be expressed. E. None of the choices given is true.
The conditions normally present in food such as moisture, acidity and nutrients are referred to as
A. extrinsic factors. B. intrinsic factors. C. endogenous factors. D. exogenous factors
The following statements regarding penicillin production and applications are true EXCEPT
A) Penicillin is a secondary metabolite produced by a filamentous fungus. B) Penicillin derivatives can be produced by biosynthetic or semisynthetic methods. C) Natural penicillin (penicillin G) inhibits a wide spectrum of bacteria. D) Penicillin selection method is used to enrich the auxotrophic mutations. E) -lactamases, which cause penicillin resistance, are easily transferable when they are located on plasmids.
For an atom to achieve maximum stability and become chemically inert, what must occur?
A) Ionization occurs. B) Its outermost energy shell must be completely filled with electrons. C) The number of electrons must equal the number of protons. D) Electron pairs are shared.