The heart in a human embryo begins to beat about ____ after fertilization
a. 5 days
b. 3 weeks
c. 7 weeks
d. 9 weeks
e. 12 weeks
ANSWER: b
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The nucleotides within DNA are composed of a
A. phosphate group, ribose sugar, and nitrogenous base. B. sulfur group, ribose sugar, and nitrogenous base. C. phosphate group, deoxyribose sugar, and nitrogenous base. D. sulfur group, deoxyribose sugar, and nitrogenous base. E. phosphate group, hexose sugar, and nitrogenous base.
The stem cells from which sperm cells descend are called
A) spermatogonia. B) secondary spermatocytes. C) spermatids. D) patagonia.
Once in the ocean, most of the available phosphorous ____
a. enters marine food webs b. enters ocean plants c. becomes ionized d. precipitates out of solution e. enters a gaseous phase
During the fermentation of one molecule of glucose, the net production of ATP is
A) six molecules. B) one molecule. C) three molecules. D) two molecules. E) eight molecules.