The clonal selection theory implies that
A. antigens activate specific lymphocytes.
B. related people have similar immune responses.
C. memory cells are present at birth.
D. the body selects which antigens it will respond to.
E. only certain cells can produce interferon.
Answer: A
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A mutualism in which each species can live without the other is termed
A. a facultative mutualism. B. an obligate mutualism. C. a trophic mutualism. D. a dispersive mutualism. E. a defensive mutualism.
The number of individuals occupying a unit of habitat (volume or area) is the ___________.
A. distribution B. carrying capacity C. population density D. population size E. birth rate
Protein synthesis requires the use of mRNA, which
A) is made in the nucleolus. B) must be made by the ribosomes. C) is translated by the ribosomes into the amino acid sequences of proteins. D) carries the message to the nucleus to synthesize new DNA during cell division.
Well-developed vascular systems are absent in all of the following except
A. hornworts. B. Pterophytes. C. liverworts. D. Charophytes. E. mosses.