When division of the zygote reaches the eight-cell stage and the planes of cleavage of the upper four cells line up with those of the bottom four cells so that two tiers of cells result, one directly above the other, the type of cleavage is called
A. direct cleavage.
B. spiral cleavage.
C. indirect cleavage.
D. protostome cleavage.
E. radial cleavage.
E. radial cleavage.
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Water can mingle with other elements because it is a:
a. heating agent. b. solvent. c. solid. d. vapor. e. nonpolar molecule.
Which of the following is the primary source of energy for chemoautotrophs?
a. inorganic molecules b. living organisms c. previously living organisms d. sunlight
In peas, the yellow allele is dominant over the green allele. A plant with yellow peas was crossed to a plant with green peas. The resulting plants were 50% yellow and 50% green. What is the genotype of the parents in this cross?
A) YY × yy B) YY × Yy C) Yy × yy D) Yy × Yy E) yy × yy
Each of the following is a category into which proteins encoded by oncogenes fit except
A) growth factors. B) signal receptors. C) plasma membrane-associated GTP-binding proteins. D) cell cycle regulators. E) P450 cytochromes.