The active maintenance of a constant environment is referred to as:
A. homeostasis.
B. equilibrium.
C. stability.
D. symmetry.
E. balance.
Answer Key: A
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What are the characteristics of stem cells? Check all that apply.
_____ Totipotent stem cells are part of a committed pathway within one cell lineage that will give rise to one specific cell type. _____ Pluripotent stem cells are descendants of the totipotent stem cells of the embryo. _____ A fertilized egg is a type of totipotent stem cell. _____ Pluripotent stem cells can differentiate into any cell type, except for totipotent stem cells and the cells of the placenta.
Mothers and teachers often say they need another pair of eyes on the backs of their heads. And another pair of hands would come in handy in many situations. You can imagine that these traits would have been advantageous to our early hunter-gatherer
ancestors as well. According to sound evolutionary reasoning, what is the most likely explanation for why humans do not have these traits? A) Because they actually would not be beneficial to the fitness of individuals who possessed them. Natural selection always produces the most beneficial traits for a particular organism in a particular environment. B) Because every time they have arisen before, the individual mutants bearing these traits have been killed by chance events. Chance and natural selection interact. C) Because these variations have probably never appeared in a healthy human. As tetrapods, we are pretty much stuck with a four-limbed, two-eyed body plan; natural selection can only edit existing variations. D) Because humans are a relatively young species. If we stick around and adapt for long enough, it is inevitable that the required adaptations will arise.
Which of the following is a characteristic of the third line of defense that makes it significantly different from the second line?
A) The response is specific to a single antigen. B) The initial response is very rapid, beginning in minutes to a couple of hours. C) The response is effective on a broad range of antigens. D) The response to a second exposure is similar to the response to a first exposure. E) The responding cells are a variety of cell types.
The first day of football practice was rough on the squad. During practice, the players complained of cramps and sore muscles. Although there is evidence to suggest that many different factors may contribute to this, which of the following is most likely to play a role in the soreness?
A. carbon monoxide B. alcohol C. lactate D. carbon dioxide E. glucose