Since the Industrial Revolution, the amount of methane in the atmosphere has __________,
and the amount of nitrous oxide has __________.
a. decreased; decreased
b. decreased; increased
c. increased; decreased
d. increased; increased
D
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Negative feedback loops to the hypothalamus and the pituitary operate to regulate the levels of ____, the most
important regulator of thyroid hormone secretion.
a. TRH b. thyroid hormone c. TSH d. ADH e. calcitonin
The respiratory systems of fish and birds are similar in that both______________.
A. utilize air sacs. B. have similar partial pressures of oxygen in the environmental medium. C. have unidirectional flow of the environmental medium over the gas exchange surfaces. D. employ countercurrent exchange.
When crossing over occurs, part of a chromatid on one chromosome breaks off and switches positions with the matching portion of a chromatid on the homologous chromosome. How does crossing over affect the possible genetic combinations in the offspring formed from these gametes?
A) Crossing over increases the number of possible genetic combinations in the offspring. B) Crossing over has no effect on the possible genetic combinations in the offspring formed. C) Crossing over affects only the possible genetic combinations that occur in identical twins. D) Crossing over decreases the number of possible genetic combinations in the offspring.
Describe the cancer stem cell hypothesis. How might this explain the inability of traditional cancer treatments such as radiation and chemotherapy to completely eradicate tumors?
What will be an ideal response?