On the west coast of North America, sea urchins were historically kept in check by:
a. lobsters.
b. surf perches.
c. sea otters.
d. crabs.
e. SCUBA divers.
C
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Which of the following is a role of the placenta during pregnancy? (Select all correct choices.)
A. nutrient exchange between maternal and fetal blood B. gas exchange between maternal and fetal blood C. waste exchange between maternal and fetal blood D. estrogen secretion to maintain uterine lining E. progesterone secretion to maintain uterine lining
What is a unifying feature of all animals, but is not seen outside of the animal kingdom?
A. They are terrestrial or secondarily aquatic. B. They are unicellular. C. They have immobile gametes. D. The nature of their small subunit rRNA gene sequences is different. E. They have a cell wall.
If a physician hears two "lub" sounds instead of one, then which of the following conditions is true?
a. The semilunar valves are not closing simultaneously. b. The atrial blood is flowing backward and causing the extra sound. c. The atrioventricular valves are not closing at the same time. d. The AV and semilunar valves are not closing at the same time. e. No such double sound has ever been heard.
The most reliable way to stimulate branching in a plant is to
A) apply auxin to the roots. B) remove the terminal bud. C) give short-day light treatments. D) add extra fertilizer.