Early animal embryos are composed of stem cells, unspecialized cells that are capable of dividing and renewing themselves for long periods
If a stem cell divides by mitosis so that one cell eventually becomes part of the brain and the other cell becomes part of a salivary gland, the cells have
A) differentiated.
B) diffused.
C) taken up genes from surrounding cells.
D) lost genes.
E) increased their genetic variability.
A
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Humans acquire infection with Trichinella tissue nematode by ingesting undercooked meat that contains the infective encysted larvae. In which tissue do these larvae encyst?
a. Brain b. Meninges c. Myocardium d. Striated muscle
What enzyme catalyzes the attachment of amino acids to tRNA molecules?
A. helicase B. topoisomerase C. aminoacyl-tRNA synthetase D. ribosome E. translation factor
In a strand of DNA, a cytosine base has been replaced by guanine. What kind of mutation has occurred?
a. frameshift mutation b. transition substitution c. transversion substitution d. translocation
Carbon dioxide is a pollutant because it
a. is absorbed by the ocean and converted into insoluble carbonates. b. is utilized when fossil fuel is burned. c. is a waste product of photosynthesis. d. cannot be recycled at a rate equal to its present production. e. is replacing oxygen as the most abundant gas in the air