What is a substance that regulates development by affecting cells in a concentration-dependent manner?
a. gene
b. nucleus
c. cytoplasm
d. morphogen
e. cytokine
d
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When a dorsal lip from a newt is attached to the ventral side of another embryo, it results in
a. two separate newts. b. two attached newts. c. survival of only the original newt. d. death of the newt. e. no observable result.
Currently, two extant elephant species (X and Y) are classified in the genus Loxodonta, and a third species (Z) is placed in the genus Elephas. Thus, which statement should be true?
A) Species X and Y are not related to species Z. B) Species X and Y share a greater number of homologies with each other than either does with species Z. C) Species X and Y share a common ancestor that is alive today. D) Species X and Y are the result of artificial selection.
The Social Security fund is maintained by a federal tax on the earnings of employed people. Which group of workers should be encouraged to live temporarily in the country?
A) young married couples B) elderly females C) young unmarried males D) retired couples
HIV can evade host antibodies by
A) remaining an inactive provirus. B) causing cell-to-cell fusion. C) remaining an inactive provirus, causing cell to cell fusion, and virions remaining latent in vacuoles. D) lowering the CD4+ cell count. E) virions remaining latent in vacuoles.