A positive antibody titer indicates
A) previous exposure to an antigen.
B) active infection.
C) latent disease.
D) a healthy individual.
Answer: A
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The essential protective role for T cell immunity is protection from
A) viruses. B) extracellular pathogens. C) bacteria. D) intracellular pathogens.
The DNA of gene X in humans has been isolated, cloned, and sequenced and is 8000 base pairs in length. From cells that were actively transcribing gene X, a cDNA library was made. In this case, gene X was found to produce from an mRNA that was 4200 bases in length. The most probable explanation of these results is that
A) there was no mRNA in the cells of the mRNA used to make the cDNA library. B) the DNA encoded introns that were excised during mRNA processing. C) a mutation resulted in a large loss of this particular gene. D) reverse transcription of the mRNA isolate was not complete. E) none of the above
For which discovery are Watson and Crick famous?
a. determining the presence of nuclein (DNA) in pus cells b. determining the three-dimensional structure of DNA c. determining the role of DNA as the genetic material d. determining what chemical components are in DNA
Which adaptation is a key characteristic of annelids that greatly increases their flexibility and mobility?
A) complete digestive tract B) exoskeleton C) segmentation D) three true tissue layers