Which of the following structures is considered to be the pacemaker of the heart?
a. atrioventricular node
b. sinoatrial node
c. atrioventricular bundle
d. Purkinje fibers
e. intercalated discs
B
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If you skip a meal, which condition is most likely to occur?
a. Insulin levels will rise. b. Glucagon levels will rise. c. Glycogen will be converted to glucose. d. Insulin levels will rise, and glycogen will be converted to glucose. e. Glucagon levels will rise, and glycogen will be converted to glucose.
The human heart
a. contracts as a result of stimuli from the sinoatrial node. b. contracts only as a result of nerve stimulation from the central nervous system. c. is activated primarily through the autonomic nervous system. d. rate is primarily under the control of the atrioventricular node. e. is independent of all nervous control
A pollen grain coat is composed of which of the
following? a. sporopollenin b. cellulose c. peptidoglycan d. exopolysaccharides e. none of these
The streamlined bodies seen in sharks, tuna, and dolphins is most likely due to
A. a recent shared common ancestor. B. the physical properties of water. C. different selection pressures. D. imperfect design. E. the need to escape fast-moving predators.