Which one of the following steps occurs during the absolute refractory period?
A) The neuron cannot generate an action potential.
B) Sodium channels open, releasing sodium ions into the neuron, which causes potassium channels to close.
C) Sodium channels open, which causes potassium channels to open.
D) A nerve impulse fails to reach threshold.
E) Potassium channels open, releasing potassium ions from the neuron; sodium channels close.
A
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Hemophilia A is an X-linked recessive disorder. If a normal man marries a woman who is a carrier, what fraction of their sons will have hemophilia?
A. 0% B. 75% C. 100% D. 25% E. 50%
Cell-mediated immunity most directly involves the destruction of diseased and/or cancerous cells by ____________
Fill in the blank(s) with the appropriate word(s)
Gradualism is rarely observed in the fossil record because:a
too may species are extinct. b. the fossil record is incomplete. c. not enough species have evolved. d. very few instances of speciation have been observed. e. more scientists believe in the model of punctuated equilibrium.
Based on the size of the sagittal crests in these figures, which animal has the most powerful bite?
What will be an ideal response?