You had a cold last month and you caught another one this month from your daughter. What is the most likely cause
of this?
a. Memory cells were not formed as a response to the first cold.
b. The antibodies formed as a response to the first cold were degraded.
c. The two cold viruses are significantly different.
d. Your T cells are not working properly.
e. Your antigen-presenting cells do not recognize the second cold virus.
c
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XH2 + NAD+ ? X + NADH + H+. In the preceding equation, NAD+ is said to be:
a. an enzyme. b. storing two hydrogen atoms. c. reduced. d. oxidized. e. a catalyst.
In instances in the eukaryotic genome, DNA sequences represent evolutionary vestiges of duplicated copies of genes. What are such regions called and what are their characteristics?
What will be an ideal response?
The lifeline between the embryo and the placenta ________
A) is derived from the yolk sac B) is derived from the amnion C) is called the "chorion" D) is called the "umbilical cord"
Which of the following is true about extinction?
a) Commercial hunting and fishing are careful not to deplete animal reserves. b) There are many causes of extinctions and an animal or plant may go extinct for any of a combination of these factors. c) Overexploitation by hunting and fishing is the foremost threat to tropical animals and plants. d) Introduction of new alien species helps preserve biodiversity and slow extinction. e) Without human activity, all species would survive and there would be no extinctions.