What caused the greatest mass extinction, in terms of species lost, at the end of the Permian?
a. global cooling
b. sea level decline
c. asteroid impact
d. overhunting by humans
e. increased volcanic activity
ANSWER: e
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The ratio of toxic dose to therapeutic dose is called the
A. therapeutic index. B. phenol coefficient. C. susceptibility quotient. D. toxicity index.
In transformation, cells
a. take up pieces of DNA that are released as other cells disintegrate. b. take up pieces of DNA through infection of a virus. c. replicate DNA molecules. d. make replicate copies of one another. e. generate their own DNA.
The female gametophyte is the
a. flower. b. ovule. c. embryo sac. d. carpel. e. ovary.
Genes that have homologs in a variety of species have been discovered through the analysis of genome sequences
In fact, it is not uncommon to find a family of homologous genes encoding proteins that are unmistakably similar in amino acid sequence in organisms as diverse as budding yeast, archaea, plants, and humans. Even more remarkably, many of these proteins can substitute functionally for their homologs in other organisms. Explain what it is about the origins of cells that makes it possible for proteins expressed by homologous genes to be functionally interchangeable in different organisms.