Which of the following human extraembryonic
membranes is the first site of blood cell
formation and the source of germ cells?
a. amnion
b. yolk sac
c. chorion
d. allantois
e. none of these
B
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Urine cannot escape back to the ureter from the bladder because there is/are blocking the way.
a. A valve b. mucosa c. Two valves d. A flap of muscle
Which muscle makes up the bulk of the shoulder?
a. biceps brachii b. pectoralis major c. triceps brachii d. deltoid e. trapezius
Why does DNA synthesis only proceed in the 5? to 3? direction?
a. Because DNA polymerases can only add nucleotides to the 3? end of a polynucleotide strand. b. Because the 3? end of the polynucleotide molecule is more electronegative than the 5? end. c. Because that is the direction in which the two strands of DNA unzip. d. Because that is the only direction that the polymerase can be oriented. e. Because the chromosomes are always aligned in the 5? to 3? direction in the nucleus.
Research on flat-tailed horned lizards demonstrated that natural selection favored lizards that ______.
a. buried themselves faster when startled b. searched for ants hidden under logs c. had longer horns on the rear of the skull d. ran faster when exposed to bright sunlight