A tracheid is:
A. a gametophyte cell
B. a small branch of an insect trachea
C. a seed-bearing stem
D. a specialized vascular cell
E. a reproductive chamber
D. a specialized vascular cell
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If red flowers (R) is dominant over white flowers (r), plants with RR ____
a. are heterozygous b. are homozygous dominant c. have red flowers d. have white flowers e. have pink flowers
Which of the following is true concerning transport
proteins in the neuron membrane? a. Only sodium is actively transported. b. Only potassium is actively transported. c. Passive transporters with open channels prevent ions from leaking across the membrane. d. Active transporters move ions against their concentration gradients. e. It takes energy to move ions through passive transporters.
The amount of life that an ecosystem can support is determined primarily by the
A) number of producers and their efficiency. B) number of heterotrophs. C) efficiency of the consumers. D) number of chemoautotrophs. E) efficiency of the heterotrophs.
The process of human X-chromosome inactivation in female cells:
A. is more common for the paternal X chromosome than the maternal X chromosome. B. condenses one copy of the X chromosome into heterochromatin. C. is necessary to ensure that only Y chromosome genes are expressed in some cells. D. All of the choices are correct.