Eukaryotic cells are thought to have
a. appeared about 2.1 billion years ago.
b. first appeared as parts of multicellular organisms.
c. evolved before prokaryotic cells.
d. developed when mitochondria grew much larger in size that they had been previously.
e. first appeared with tough cell walls.
A
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Thick-skinned rhinoceroses and elephants were once classified together as pachyderms. They actually descended from different ancestors that in turn evolved from a thin-skinned common ancestor that was not included in the pachyderms. Pachyderms were therefore, as a taxon,
A. polyphyletic. B. polygenetic. C. paraphyletic. D. a supergroup. E. a kingdom.
Why is the protein-first hypothesis not accepted by most scientists?
a. Proteins cannot be catalysts. b. There is no known mechanism of protein self-replication. c. Of all of the macromolecules, only DNA can self-replicate. d. There is no evidence that proteins can store information. e. Proteins are too complex to have been the first "polymers of life."
Once a pollen tube lands on a compatible stigma
a. chemical cues guide the pollen tube from the stigma to the embryo sac of an ovule. b. that pollen tube continues on to another ovule. c. other pollen tubes are attracted to that ovule. d. other pollen tubes can penetrate that ovule more easily. e. the flower dies to prevent further pollination
Restriction endonucleases were discovered by ________.
A. Arber and Smith B. Jackson, Symons, and Berg C. Temin and Baltimore D. Boyer and Cohen