Sajjad1994 wrote:
It was once believed that cells grown in laboratory tissue cultures were essentially immortal. That is, as long as all of their needs were met, they would continue dividing forever. However, it has been shown that normal cells have a finite reproductive limit. A human liver cell, for example, divides 60 times and then stops. If such a cell divides 30 times and then is put into a deep freeze for months or even years, it “remembers” where it stopped dividing. After thawing, it divides another 30 times—but no more.
If the information above is accurate, a liver cell in which more than 60 divisions took place in a tissue culture CANNOT be which one of the following?
(A) an abnormal human liver cell
(B) a normal human liver cell that had been frozen after its first division and afterward thawed
(C) a normal cell that came from the liver of an individual of a nonhuman species and had never been frozen
(D) a normal liver cell that came from an individual of a nonhuman species and had been frozen after its first division and afterward thawed
(E) an abnormal cell from the liver of an individual of a nonhuman species
LSAT Prep Test 8
OFFICIAL EXPLANATION
(A) No. It would be abnormal since a normal human liver cell would divide “60 times and then stop.”
(B) Yes. The passage is explicit that a normal cell cannot divide more than 60 times regardless of whether it was frozen and afterwards thawed. “It ‘remembers’ where it stopped dividing.”
(C) No. Since the cell is normal, it cannot divide indefinitely. However, since it is not a human liver cell it may have a limit of more than 60 divisions—we don’t know. This answer choice is essentially the same as choice (D) since the passage implies that it is irrelevant whether the cell has been frozen—“it divides 60 times and then stops.”
(D) No. Since the cell is normal, it cannot divide indefinitely. However, since it is not a human liver cell it may have a limit of more than 60 divisions—we don’t know. This answer choice is essentially the same as choice (C) since the passage implies that it is irrelevant whether the cell has been frozen—“it divides 60 times and then stops.”
(E) No. All we can say is that it is not a normal human liver cell. Since it divided more than 60 times, it could be an abnormal human cell, an abnormal non-human cell, or a normal nonhuman cell.
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