Which one of the following statements about the trypanosome causing African sleeping sickness does not explain why the disease has been difficult to control?
A. Trypanosomes have a protective glycoprotein coat.
B. Trypanosomes have many variable antigen genes.
C. Rearrangement of antigen genes takes place during the asexual cycle.
D. By infesting the red blood cells, trypanosomes can "hide" from the immune system.
E. Only one gene determining the antigenic nature of the glycoprotein coat is expressed at a time.
D. By infesting the red blood cells, trypanosomes can "hide" from the immune system.
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The mechanism of acquired, high-level resistance to vancomycin involves:
a. enzymatic destruction of the antibiotic. b. altered antibiotic targets. c. decreased intracellular uptake of the drug. d. production of altered cell wall precursors that do not bind the antibiotic with suffi-cient avidity.
A molecule of water in the middle of a chunk of ice will usually have ____ hydrogen bonds with other
water molecules.
a. 3 b. 3.4 c. 6 d. 4 e. 2
There are how many different kinds of amino acids
in proteins? a. 3 b. 6 c. 12 d. 20 e. 28
Major changes in ocean conditions during the early Cambrian period were probably linked most closely to the evolution of __________.
a. cyanobacteria b. algae c. suspension-feeding animals d. large and motile predatory animals e. vertebrates