The geologic time scale is subdivided on the
basis of
a. the appearance of different radioactive
isotopes in different strata.
b. levels of background extinction.
c. periods of mass extinction.
d. the appearance of different radioactive
isotopes in different strata and levels of
background extinction.
e. the appearance of different radioactive
isotopes in different strata, levels of
background extinction, and periods of mass
extinction.
C
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The hormones secreted from the adrenal cortex, like cortisol, which raise the blood glucose level are collectively called _______
A. Mineralocorticoids
B. Gonadocorticoids
C. Corticosteroids
D. Glucocorticoids
Which sentence best describes the role of the signal recognition particle (SRP)?
a. It activates gene expression. b. It assists in polyadenylation of mRNA. c. It assists in mRNA splicing. d. It temporarily blocks translation.
Which of the following is considered a likely explanation for the events of the Cambrian explosion?
A) Complex predator-prey relationships and increased atmospheric oxygen levels promoted animal diversification. B) A great surge of volcanic activity was triggered by significant movements of the continental plates and possibly by an asteroid impact. C) Solar flares led to increased UV radiation intensity, which in turn promoted a high rate of mutation. This led to rapid diversification of animals. D) The massive growth of swamp vegetation depleted the atmosphere's carbon dioxide and eventually cooled the Earth's climate.
Biologists use the term segregation to describe _____.
A) how dominant and recessive genes remain separated from one another over many generations B) how gene pairs separate during meiosis and end up in different gametes C) why mating a black horse and a white horse produces either black or white but never gray offspring D) how, after fertilization, a gene from a sperm cell recombines with its pair from an egg