It is believed that the two main reasons for mass extinctions in Earth's history have been
A. collision between Earth and a large celestial body and human intervention.
B. global warming and human intervention.
C. human intervention and shifting of Earth's continents.
D. global warming and shifting of Earth's continents.
E. collision between Earth and a large celestial body and shifting of Earth's continents.
E. collision between Earth and a large celestial body and shifting of Earth's continents.
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If a helical turn is removed from a closed-circular DNA molecule:
A. only supercoiling will occur. B. only strand separation will occur. C. supercoiling and/or strand separation will occur. D. cruciform DNA will likely form. E. solenoidal DNA will likely form.
What animal has kidneys that are so efficient that it never has to drink water and can obtain all of its water from its food?
A. camel B. desert lizard C. gerbil D. pocket mouse E. kangaroo rat
Hypothesis I: A flavin pigment absorbs blue light; this pigment then activates the proton pump.Hypothesis II: When CO2 concentration rises, a membrane receptor inactivates the proton pump.Air with varying amounts of CO2, within the ranges found in nature, is forced across leaf surfaces and into sub-stomatal cavities; this produces closure of the stomata.
A. Supports both hypothesis I and II. B. Supports only hypothesis I. C. Supports only hypothesis II. D. Supports neither hypothesis.
The domain Archaea includes prokaryotes that are
A) endospore formers. B) intracellular parasites. C) members of the deeply branching bacteria. D) human pathogens. E) hyperthermophiles.