Because of some of the problems with explaining how the first RNA organisms originated, an alternative possibility
has been proposed in which ____.
a. proteins and RNA evolved simultaneously
b. DNA existed before RNA
c. lipids functioned as enzymes
d. a different form of life existed before the RNA world
e. viruses functioned as carriers for RNA
ANSWER: d
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Sidearms are attached to ________.
A) B tubules B) A tubules C) central pairs D) radial spokes E) interdoublet nexin
Elephants are large animals because they
a. have bigger cells. b. possess expandable cells. c. are made of a greater number of cells. d. have bigger cells and are made of a greater number of cells. e. have bigger cells that are expandable and of greater number
The most productive region of a lake is the __________ zone
a. neritic b. limnetic c. profundal d. littoral e. oceanic
Which of these cell types is not involved in cell-mediated immunity?
A) plasma cells B) TH1 cells C) T helper cells D) T regulatory cells E) T cytotoxic cells