In summer, the upper and lower levels of a lake are separated by the:
a. limnetic zone
b. thermocline
c. littoral zone
d. lentic zone
e. eutrophic zone
b
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Oysters generally settle at right angles to tidal currents. These currents:
a. carry food away from the oysters. b. clear sediments from the oysters. c. help them avoid oyster drills. d. deposit sediments among the oysters.
Observable functional or physical traits are the
a. phenotype. b. allelotype. c. homotype. d. heterotype. e. genotype.
In their famous experiment, which of the following would Meselson and Stahl have observed after one cycle of replication in 14N medium if DNA replication was conservative?
A) DNA molecules containing one strand of 15N-DNA and one strand of 14N-DNA B) DNA molecules containing two 15N-DNA strands only C) DNA molecules containing two 14N-DNA strands only D) An equal number of DNA molecules containing two 15N-DNA strands and DNA molecules containing two 14N-DNA strands. E) A mix of DNA molecules corresponding to A and B.
One characteristic of the class Holothuroidea is that they:a
are predators that consume partially digested prey. b. are mostly extinct species. c. have a reduced endoskeleton consisting of microscopic plates embedded in the body wall. d. have moveable spines that are used to facilitate locomotion. e. have a distinct central disk with very long, slender arms