The excitatory signal generated by the cardiac
pacemaker spreads from fiber to fiber via
a. gap junctions.
b. tight junctions.
c. gated channels.
d. desmosomes.
e. sodium-potassium channels
A
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Which of the following statements concerning metastatic tumors is FALSE?
a. They are examples of neoplasms. b. They contain cancer cells. c. They have escaped controls on cell division. d. They are caused by the altered expression of genes. e. They are localized in one part of the body.
Zooplankton are heterotrophs.
Answer the following statement true (T) or false (F)
A newly synthesized polypeptide will ultimately be located within the phospholipid bilayer of the plasma membrane. When this polypeptide folds to form its tertiary structure, the ________ amino acid R-groups will most likely be facing outward.
A. hydrophobic B. hydrophilic