The electrical stimulus for each human heartbeat begins in the
A. left atrium at the sinoatrial node.
B. right ventricle at the atrioventricular node.
C. pulmonary trunk at the sinoatrial node.
D. right atrium at the atrioventricular node.
E. right atrium at the sinoatrial node.
Answer: E
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How does the RecA protein contribute to the increased expression of SOS genes?
A. RecA protein competes with LexA protein for binding to the operator sequences. B. RecA protein binds to LexA protein bound to the operator, directly lowering the affinity of LexA protein for DNA. C. RecA protein binds to free LexA protein, mediating the self-cleavage of the repressor. D. RecA protein binding to the promoter region recruits RNA polymerase.
Which is not a common method of sampling? a. Counting all individuals in the region
b. Mark-recapture sampling. c. Counting individuals in a representative area. d. Observing evidence of an organism's presence in an area.
In the nitric oxide signaling pathway, nitric oxide activates an enzyme that can convert many molecules of GTP into molecules of cGMP. cGMP is a small molecule that can diffuse through the cytoplasm and bind to an enzyme called protein kinase G (PKG). Binding of cGMP to PKG leads to a change in the confirmation of PKG that leads to its activation. What type of signaling molecule is cGMP?
A. Adapter protein B. Enzyme C. Second messenger D. Scaffold
Following ovulation, rising levels of estrogen
A) stimulate the endometrium to continue to proliferate. B) inhibit the production of progesterone. C) initiate a hormone cascade that triggers LH to rise, then FSH, followed by a sharp decline in GnRH. D) promote the release of the "old" endometrium. E) prevent implantation of the zygote.