The main phenomenon that increases the efficiency of gas exchange in fish gills is the
A. back-and-forth movement of water that maximizes oxygen uptake.
B. high degree of oxygen saturation of water.
C. very high blood pressure found in the circulatory system of fishes.
D. co-current exchange mechanism.
E. countercurrent exchange mechanism.
Answer: E
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Of the enzymes associated with the metabolism of lactose with the lac operon, the one associated with transport of lactose into the cell is
A) ?-galactosidase. B) transacetylase. C) galactoside permease. D) ?-lactase. E) lactose translocase.
An atom is in its most stable state when
a. the number of electrons equals the number of protons. b. the number of neutrons equals the number of protons plus number of electrons. c. there are electron vacancies in the inner most shell. d. there are no electron vacancies in the outer shell. e. more than one of these is possible
ACTH
a. is secreted by the posterior pituitary. b. has target cells in the autonomic nervous system. c. has target cells in the adrenal cortex. d. has target cells in the adrenal medulla. e. initiates the autoimmune response.
Select the proper order of the propagation of an electrical (depolarization) signal in the heart
a. AV node ?Purkinje fibers ?SA node b. AV node ?SA node ?Purkinje fibers c. Purkinje fibers ?AV node ?SA node d. Purkinje fibers ?SA node ?AV node
e. SA node ?AV node ?Purkinje fibers