A group is considered paraphyletic if
A. all members of the group share a common ancestor.
B. not all descendants of the common ancestor are included.
C. the common ancestor of the group is not included in the group.
D. the group does not contain the most recent common ancestor.
E. it is the most parsimonious grouping.
B. not all descendants of the common ancestor are included.
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Which one of the following cell types would likely have the most extensive system of smooth endoplasmic reticulum?
A. skin cells B. pancreatic cells that secrete digestive enzymes C. testicular cells D. central nervous system cells E. muscle cells
All of the following events occur during T-dependent activation of a B cell EXCEPT
A. an antigenic fragment held within an MCH Class II molecule of a dendritic cell binds to a specific T cell receptor on a naïve T-helper cell. B. specific cytokines from the T helper cells stimulate maturation and complete activation of the antigen-stimulated B cell. C. antigen within MCH class II molecule is presented by B cell to an activated T helper cell. D. antigen binds to specific B cell receptor molecules. E. antigen bound to the B cell receptor is internalized and transferred to an MHC class II molecule which then moves to the plasma membrane. F. There are no exceptions. All of these events occur during T-depedent activation of B cells.
A gene pool is
A. the genes that are unique to a species. B. all the genes in a population. C. all the similar genes in a gene family. D. a swimming hole for geneticists. E. a group of species that look alike but are not located in the same area at the same time.
Which of the following is (are) found in many veins that help direct blood flow in one direction only: toward the heart?
A) valves B) lymph nodes C) myocardium D) pericardium