Research into the physiological causes of agingthat process character

Question

Research into the physiological causes of aging—that process characterized by decreased survival capacity on the part of an organism—has produced few undisputed facts. Until the 1960's, many scientists agreed with Carrel’s view of aging. Carrel claimed that animal cells cultivated in an artificial environment outside the animal's body were imperishable because they could divide indefinitely. If such cells could perpetuate themselves indefinitely when sustained by an optimal environment, Carrel concluded chat the causes of aging were located in the interaction of cells within an inadequate tissue environment. However, Hayflick’s experiments, using cells cultivated in a similar artificial environment, decisively demonstrated that normal (though not abnormal) cells have only a limited life: span and so are not “immoral.” These experiments fundamentally weakened Carrel’s conclusion since they strongly suggested that aging resulted from changes in the properties of cells themselves. Hayflick added that one explanation for Carrel's long-lived cells was that Carrel might have inadvertently introduced new living cells when he renewed the nutrient solution in which he grew his cultivated cells.

Yet if scientists currently agree that the causes of aging are located at the cellular level, they disagree about which ceils are responsible for aging. One hypothesis maintains that aging is caused by loss of or injury to postmitotic cells (cells incapable of division); this hypothesis has received some support from experimenters. Experiments by McCay, for example, demonstrated that rats live longer than usual when underfed. Although scientists have proposed several explanations for this longevity, proponents of the postmitotic hypothesis argue that underfeeding protects postmitotic cells from disease. If aging is postponed because postmitotic cells are protected, then the hypothesis that aging is caused by damage to postmitotic cells is indirectly supported. On the other hand, Szilard’s experiments with mice, demonstrating that exposure to ionizing radiation shortens life, seem to weaken the postmitotic hypothesis. In these experiments, dividing, or mitotic, cells were more susceptible to radiation damage than were postmitotic cells. If radiation shortens life and primarily affects mitotic cells, perhaps these cells are responsible for aging. In fact, many scientists believe that loss of or damage to mitotic cells causes aging. Burnet, a Proponent of one version of this second hypothesis, argues that damage to mitotic lymphocytes promotes aging by exciting the body's immunological system to attack the body's own tissue. Burnet’s clever hypothesis is weakened, however, by the fact chat immunological defects are twice as common in women as in men, yet, On the average, women live considerably longer than men.

Resolution of the mitotic versus postmitotic debate is made difficult by the shortage of suitable research Organisms (species with short life spans and genetic uniformity, among other characteristics); if more of such species could be located, conclusive experimentation on aging might be possible.    1 
 1. According to the passage, the research of Carrel and Hayflick had which of the following in common?

I. Cultivation of an animal's cells outside of the animal’s body
II. Location of the causes of aging only in the properties of cells themselves
III. Investigation of the ability of cells to divide indefinitely

(A) II only
(B) Ill only
(C) I and H only
(D) I and III only
(E) I, I, and II

2 
 2. According to the passage, Hayflick believed that Carrel might have made which of the following errors in his research?

(A) Persistent failure to analyze the behavior of abnormal cells
(B) Reliance on outmoded data about aging
(C) Study of postmitotic cells at the expense of investigating mitotic cells
(D) Provision of an inadequate nutrient solution for cultivated cells
(E) Inadequate control of the substances added in the nutrient solution

3 
 3. The passage suggests that abnormal cells differ from normal cells in those abnormal cells

(A) are not capable of division
(B) do not have a limited life span
(C) are more susceptible to injury than are normal cells
(D) may not excite the body’s immunological system to work against the body’s own tissue
(E) are more frequently studied as a possible cause of aging than are normal cells

4 
 4. The author suggests that some scientists have responded to the results of McCay’s experiments by doing which of the following?

(A) Accounting for the results by explanations other than the one offered by proponents of the postmitotic hypothesis
(B) Interpreting the results as weakening both the mitotic and the postmitotic hypotheses of aging
(C) Arguing that the results are more conclusive in demonstrating that damage to postmitotic cells Causes aging than in demonstrating that protection of such cells tends to Postpone aging
(D) Using the results more often to disprove the mitotic hypothesis of aging than to confirm the postmitotic hypothesis
(E) Using the results to dispute the claims of those who argue thar disease is the primary cause of aging

5 
 5. According to the Passage, experiments in which rats were underfed indicate that

(A) an animal’s normal life Span is difficult to predict
(B) rats have greater longevity when underfed than do other research animals
(C) protection of an animal's postmitotic cells does not seem to affect the aging process in the animal
(D) efforts by researchers to locate the causes of aging in the properties of mitotic cells are unlikely to succeed
(E) the length of a rat's life is related to the amount of food it eats

6 
 6. According to the Passage, ionizing radiation is thought to have which of the following effects on aging?

(A) Promotion of aging by damaging mitotic cells
(B) Promotion of aging in mice more than in humans
(C) Promotion of aging because such radiation is the primary cause of immunological defects
(D) Promotion of aging despite the fact that such radiation does not affect postmitotic cells
(E) Promotion of aging as well as its Postponement

7 
 7. The author mentions the experiments of Szilard most probably in order to

(A) give an example of research on aging that has prompted contradictory interpretations by scientists
(B) refute the data from McCay’s experiments concerning the effects of underfeeding on rats
(C) prove thar ionizing radiation is not the most important factor in promoting the aging process
(D) support the contention that mitotic and postmitotic cells are equally affected by ionizing radiation
(E) suggest that scientific research does not entirely confirm the postmitotic hypothesis of aging

8 
 8. The author suggests that Burnet’s hypothesis about the causes of aging is one of a number of hypotheses that

(A) are weakened by the findings of Szilard
(B) have underestimated the role of the immunological system in promoting aging
(C) have conclusively weakened the postmitotic hypothesis about aging
(D) stress the role of mitotic cells in promoting aging
(E) offer explanations of aging that are different for men than for women

9 
 9. Which of the following statements would be most likely to follow the last sentence of the passage?

(A) Most scientists believe that such experimentation will probably lead to a revival of Carrel’s hypothesis of aging.
(B) Some scientists believe that such experimentation might be facilitated by the use of the rotifer, an organism that, it has been discovered, meets several requirements set by researchers.
(C) Many scientists believe that the most conclusive experiments will be conducted with Organisms that lack genetic uniformity.
(D) Such experimentation might finally furnish support for Szilard’s research, which has been so persistently questioned by skeptical scientists.
(E) Such experimentation might finally lead Scientists to propose a new hypothesis about aging to replace the cellular model that, because of recent experimentation, is now held in wide disrepute.

Sajjad1994 · Answer

Explanation

1. According to the passage, the research of Carrel and Hayflick had which of the following in common?

Carrel:  Claimed animal cells in artificial environment outside the body were imperishable and could divide indefinitely.
 Hayflick:  Used cells in a similar artificial environment, but demonstrated normal cells have a limited life span, contradicting Carrel’s “immortal” claim.

I. Cultivation of an animal’s cells outside of the animal’s body 
Both did this (Hayflick’s experiments  “using cells cultivated in a similar artificial environment” ).   Yes.

II. Location of the causes of aging only in the properties of cells themselves 
This is not true for Carrel. Carrel believed aging was due to interaction of cells in an inadequate tissue environment (not in the cells’ intrinsic properties). Hayflick’s experiments suggested aging resulted from changes in the properties of cells themselves. So  “only in the properties of cells themselves”  is not shared.   No.

III. Investigation of the ability of cells to divide indefinitely 
Yes, both looked into that. Carrel claimed they could; Hayflick investigated and found they could not (for normal cells).   Yes.

I and III only That’s (D).

Anwer: D

Prakhar2499 · Answer

Hi  Sajjad1994 , can you post the OA's for other questions as well.

Sajjad1994 · Answer

Explanation

4. The author suggests that some scientists have responded to the results of McCay’s experiments by doing which of the following?

Look closely at the relevant part of the passage.

It says about McCay’s experiments:

"McCay... demonstrated that rats live longer than usual when underfed. Although scientists have proposed several explanations for this longevity, proponents of the postmitotic hypothesis argue that underfeeding protects postmitotic cells from disease."

This tells us:

-McCay’s results show underfeeding ---> longer rat life.
-Proponents of the postmitotic hypothesis say it’s because underfeeding protects postmitotic cells.
-But other scientists have proposed several explanations for this longevity other than that one.

That means scientists have responded by offering alternative explanations and  (A)  matches this perfectly.

(B)  is wrong it doesn’t weaken both, and not said.

(C)  is wrong, no mention that results are  “more conclusive”  for damage causing aging than protection postponing aging.

(D)  is wrong, not about disproving mitotic hypothesis.

(E)  is wrong, no focus on disputing that disease is primary cause of aging; the postmitotic proponents even said disease protection helps.

Answer: (A)

Sajjad1994 · Answer

Explanation

8. The author suggests that Burnet’s hypothesis about the causes of aging is one of a number of hypotheses that

Explanation

Look at the part where Burnet is discussed:

"In fact, many scientists believe that loss of or damage to mitotic cells causes aging. Burnet, a proponent of one version of this second hypothesis, argues that damage to mitotic lymphocytes promotes aging by exciting the body's immunological system..."

The  "second hypothesis"  refers to the mitotic hypothesis (aging caused by damage to mitotic cells).
Burnet’s is one version of it, so Burnet’s hypothesis belongs to the set of hypotheses that  "stress the role of mitotic cells in promoting aging."

(D)  matches this description exactly.

(A)  No, Szilard’s findings support mitotic hypothesis, don’t weaken it.

(B)  No, Burnet’s hypothesis actually highlights the immunological system’s role in aging via mitotic lymphocytes; not about underestimating it.

(C)  No,  “conclusively weakened”  is too strong; Szilard’s findings weaken the postmitotic hypothesis, but Burnet’s version is one of the mitotic hypotheses.

(E)  No, Burnet’s explanation isn’t different for men vs. women; instead, the fact about immunological defects’ frequency in women vs. men weakens Burnet’s idea.

Answer: D

Sajjad1994 · Answer

Explanation

9. Which of the following statements would be most likely to follow the last sentence of the passage?

Explanation

The  last sentence  says:

Resolution of the mitotic versus postmitotic debate is made difficult by the shortage of suitable research organisms (species with short life spans and genetic uniformity, among other characteristics);  if more of such species could be located, conclusive experimentation on aging might be possible.

The logical follow-up would be about finding such organisms to facilitate research.

(A)  Talks about revival of Carrel’s hypothesis, not relevant to the current debate (mitotic vs postmitotic).

(B)  This directly continues the idea: we need suitable research organisms ---> here’s an example of one that fits the criteria. Perfect logical follow-up.

(C)  Says organisms that lack genetic uniformity, but the passage says genetic uniformity is one desirable trait. So  this contradicts  the passage’s criteria.

(D)  Talks about furnishing support for Szilard’s research, but the debate isn’t about validating Szilard’s specific results, but about deciding between hypotheses.  Too narrow.

(E)  Says propose a new hypothesis to replace the cellular model, but scientists currently agree on cellular-level causes, so this undermines the current view, not likely as immediate follow-up.

Answer: B

Research into the physiological causes of agingthat process character

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Reading Comprehension (RC) Questions

Research into the physiological causes of agingthat process character

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards