It was once believed that cells grown in laboratory tissue cultures were essentially immortal. That is, as long as al...

Irina July 30, 2019

@Addison,

The author is telling us that normal cells have a finite reproductive limit. A NORMAL HUMAN LIVER cell has a limit of 60 divisions. Note that we have no information about the division limits for non-human cells, non-liver cells, abnormal cells, and any combinations thereof.

So a cell in which more than 60 divisions took place cannot be which on the following?

Let's look at the answer choices - four of them COULD be true and one CANNOT be true:

(A) is incorrect because we only know the limit that applies to NORMAL HUMAN LIVER cells, we have no information regarding abnormal cells;

(B) is correct because this exact scenario is described in the stimulus. The fact that a normal human liver cell has been frozen and then thawed cannot change its division limit, thus it is impossible for it to divide OVER 60 times;

(C) is incorrect because we have no information about the properties of the liver cell of other species, thus we cannot definitely say that it is impossible for it to divide over 60 times;

(D) is incorrect because again we have no information about liver cells of other species or the impacts of a deep freeze on their division capabilities;

(E) is incorrect because we have no information about abnormal nonhuman cells.

This question requires you to pay close attention to the wording - we are only given a specific division limit for normal human liver cells, thus all the answer choices that involve other types of cells could be true because we cannot make any inferences just based on the fact that a normal human liver cell's reproductive limit is 60.

Does this make sense?
Let me know if you have any other questions.

AddisonPatton July 30, 2019

Okay. I think I understand it now. The way the question was worded was causing me to overthink it. Thank you for your help!

Ravi August 12, 2019

@AddisonPatton, let us know if you have any other questions!

studybug October 22, 2023

Sorry, I still don't get B over A. A where "a normal human liver cell that had been frozen after its first division and afterward thawed" This answer choice does not directly contradrict a cell that divides more than 60 times - as afterward thawed does not indicate if it is still alive or not, can divide more, will stop at 60, or can divide more than 60 times. So reasoning shows it can be this.

Emil-Kunkin October 24, 2023

The answer choice is referring to cells that have already divided. We know that a normal cell, regardless of whether frozen or not, cannot divide more than 60 times, so if a cell is normal, it can never divide more than 60 times.