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Free MCAT Test Exam Braindumps (page: 5)

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Due to ever-increasing paranoia about the transmission of hepatitis and AIDS via blood transfusions and the frequent difficulty of procuring matching blood donors for patients, researchers have been working at a feverish pace to produce disease-free and easy-to-use blood substitutes. The difficulty most synthetic blood researches have had is in formulating a substance that combines qualities of sterility, high capacity for carrying oxygen to body tissues, and versatility within the human body. Three major substitute technologies have been developed to date; each has certain advantages and shortcomings.
"Red blood," the first of the blood substitute technologies, is derived from hemoglobin which has been recycled from old, dead, or worn-out red blood cells and modified so that it can carry oxygen outside the red blood cell. Hemoglobin, a complex protein, is the blood's natural oxygen carrier and is attractive to scientists for use in synthetic blood because of its oxygen-carrying capacity. However, hemoglobin can sometimes constitute a two-fold threat to humans when it is extracted from the red blood cell and introduced to the body in its naked form. First, hemoglobin molecules are rarely sterile and often remain contaminated by viruses to which they were exposed in the cell. Second, naked hemoglobin is extremely dangerous to the kidneys, causing blood flow at these organs to shut down and leading, ultimately, to renal failure. Additional problems arise from the fact that hemoglobin is adapted to operate optimally within the intricate environment of the red blood cell. Stripped of the protection of the cell, the hemoglobin molecule tends to suffer breakdown within several hours. Although modification has produced more durable hemoglobin molecules which do not cause renal failure, undesired side effects continue to plague patients and hinder the development of hemoglobin-based blood substitutes.
Another synthetic blood alternative, "white blood," is dependent on laboratory synthesized chemicals called perfluorocarbons (PFCs). Unlike blood, PFCs are clear oil like liquids, yet they are capable of absorbing quantities of oxygen up to 50% of their volume, enough of an oxygen carrying potential for oxygen-dependent organisms to survive submerged in the liquid for hours by "breathing" it. Although PFCs imitate real blood by effectively absorbing oxygen, scientists are primarily interested in them as constituents of blood substitutes because they are inherently safer to use than hemoglobin-based substitutes. PFCs do not interact with any chemicals in the body and can be manufactured in near-perfect sterility. The primary pitfall of PFCs is in their tendency to form globules in plasma that can block circulation. Dissolving PFCs in solution can mitigate globulation; however, this procedure also seriously curtails the PFCs' oxygen capacity.
The final and perhaps most ambitious attempt to form a blood substitute involves the synthesis of a modified version of human hemoglobin by genetically-altered bacteria. Fortunately, this synthetic hemoglobin seems to closely mimic the qualities of sterility, and durability outside the cellular environment, and the oxygen-carrying efficiency of blood. Furthermore, researchers have found that if modified hemoglobin genes are added to bacterial DNA, the bacteria will produce the desired product in copious quantities. This procedure is extremely challenging, however, because it requires the isolation of the human gene for the production of hemoglobin, and the modification of the gene to express a molecule that works without support from a living cell.
While all the above technologies have serious drawbacks and difficulties, work to perfect an ideal blood substitute continues. Scientists hope that in the near future safe synthetic blood transfusions may ease blood shortages and resolve the unavailability of various blood types.
We can infer that all of the synthetic blood technologies discussed in this passage:

  1. sustain submerged oxygen-dependent organisms.
  2. possess high oxygen-carrying capacities.
  3. maintain high standards of sterility.
  4. exhibit versatility in the human body

Answer(s): B

Explanation:

This is an inference question that asks you to identify a common trait of all synthetic bloods. Choice (A) states that all of the synthetic bloods discussed in the passage sustain submerged oxygen-dependent organisms. The second sentence of the third paragraph notes that PFCs possess this ability, but there is no suggestion of this in reference to any of the other blood substitutes. So choice (A) is wrong. Choice (C) is incorrect because, even though all synthetic bloods should have high levels of sterility, the passage explicitly states that the naked hemoglobin molecules of "red blood" are "rarely sterile and often remain contaminated by viruses to which they were exposed in the cell". Not all blood substitutes, then, maintain high standards of sterility. Finally, choice (D) is wrong in stating that all synthetic bloods exhibit versatility in the body.
The passage makes clear that not all blood substitutes are particularly versatile. For one thing, the naked hemoglobin of "red blood'' breaks down in the blood stream within several hours. Furthermore, PFCs tend to form globules, blocking blood circulation. Only choice (B) is mentioned in reference to all synthetic blood technologies. The second sentence of the second paragraph states that hemoglobin, the chief component of "red blood", is "attractive to scientists...because of its oxygen-carrying capacity". The second sentence of the third paragraph implies that PFCs have high oxygen-carrying capacities as it mentions that PFCs can absorb oxygen up to quantities 50% its volume. The author goes on to note, in the following sentence, that PFCs imitate real blood by effectively absorbing oxygen. Finally, the passage explicitly states in the second sentence of the fourth paragraph that the synthetic hemoglobin produced by genetically-altered bacteria "closely mimic (s)...(the) oxygen-carrying efficiency of blood". Choice (B), then, is the correct answer.



Due to ever-increasing paranoia about the transmission of hepatitis and AIDS via blood transfusions and the frequent difficulty of procuring matching blood donors for patients, researchers have been working at a feverish pace to produce disease-free and easy-to-use blood substitutes. The difficulty most synthetic blood researches have had is in formulating a substance that combines qualities of sterility, high capacity for carrying oxygen to body tissues, and versatility within the human body. Three major substitute technologies have been developed to date; each has certain advantages and shortcomings.
"Red blood," the first of the blood substitute technologies, is derived from hemoglobin which has been recycled from old, dead, or worn-out red blood cells and modified so that it can carry oxygen outside the red blood cell. Hemoglobin, a complex protein, is the blood's natural oxygen carrier and is attractive to scientists for use in synthetic blood because of its oxygen-carrying capacity. However, hemoglobin can sometimes constitute a two- fold threat to humans when it is extracted from the red blood cell and introduced to the body in its naked form. First, hemoglobin molecules are rarely sterile and often remain contaminated by viruses to which they were exposed in the cell. Second, naked hemoglobin is extremely dangerous to the kidneys, causing blood flow at these organs to shut down and leading, ultimately, to renal failure. Additional problems arise from the fact that hemoglobin is adapted to operate optimally within the intricate environment of the red blood cell. Stripped of the protection of the cell, the hemoglobin molecule tends to suffer breakdown within several hours. Although modification has produced more durable hemoglobin molecules which do not cause renal failure, undesired side effects continue to plague patients and hinder the development of hemoglobin-based blood substitutes.
Another synthetic blood alternative, "white blood", is dependent on laboratory synthesized chemicals called perfluorocarbons (PFCs). Unlike blood, PFCs are clear oil like liquids, yet they are capable of absorbing quantities of oxygen up to 50% of their volume, enough of an oxygen carrying potential for oxygen-dependent organisms to survive submerged in the liquid for hours by "breathing" it. Although PFCs imitate real blood by effectively absorbing oxygen, scientists are primarily interested in them as constituents of blood substitutes because they are inherently safer to use than hemoglobin-based substitutes. PFCs do not interact with any chemicals in the body and can be manufactured in near-perfect sterility. The primary pitfall of PFCs is in their tendency to form globules in plasma that can block circulation. Dissolving PFCs in solution can mitigate globulation; however, this procedure also seriously curtails the PFCs' oxygen capacity.
The final and perhaps most ambitious attempt to form a blood substitute involves the synthesis of a modified version of human hemoglobin by genetically-altered bacteria. Fortunately, this synthetic hemoglobin seems to closely mimic the qualities of sterility, and durability outside the cellular environment, and the oxygen-carrying efficiency of blood. Furthermore, researchers have found that if modified hemoglobin genes are added to bacterial DNA, the bacteria will produce the desired product in copious quantities. This procedure is extremely challenging, however, because it requires the isolation of the human gene for the production of hemoglobin, and the modification of the gene to express a molecule that works without support from a living cell.
While all the above technologies have serious drawbacks and difficulties, work to perfect an ideal blood substitute continues. Scientists hope that in the near future safe synthetic blood transfusions may ease blood shortages and resolve the unavailability of various blood types.
Which of the following is mentioned in the passage as a problem specific to "red blood"?

  1. "Red blood" cannot be produced in large enough quantities.
  2. "Red blood" tends to form globules that block circulation.
  3. Hemoglobin does not carry oxygen effectively.
  4. "Red blood" exhibits poor durability in the bloodstream.

Answer(s): D

Explanation:

This is a detail question that requires you to recall which of the answer choices is a problem specific to "red blood". Since "red blood" is discussed in the second paragraph of the passage, refer there for details. Choice (A) is incorrect because the passage never says that "red blood cannot be produced in large quantities". In fact, the passage never at all mentions the extent to which "red blood" can be produced. The passage only mentions quantities of production of synthetic blood in the third sentence of the fourth paragraph, where it states, in reference to genetically- altered hemoglobin, that "the bacteria will produce the desired product in copious quantities". Since the passage never mentions (A), it cannot be a problem specific to "red blood". Similarly, choice (B) distorts a detail of the passage which relates to another type of synthetic blood. The passage mentions in the fourth sentence of the third paragraph that the primary pitfall of PFCs is their tendency to form globules. The passage never says that "red blood'' forms globules. Choice (C) also is not a true statement. The second sentence of the second paragraph states that hemoglobin is the blood's natural oxygen carrier and, in fact, is attractive to scientists precisely because of its oxygen-carrying capacity. You may safely conclude from this information, then, that hemoglobin does, indeed, carry oxygen effectively and (C) is not a problem at all.
Only choice (D), which states that "red blood exhibits poor durability in the bloodstream", is mentioned in the passage as a problem specific to "red blood". In the second paragraph, the passage states that "additional problems arise from the fact that hemoglobin is adapted to operate optimally within the...cell. Stripped of the protection of the cell, the hemoglobin molecule tends to suffer breakdown within several hours". One of the criteria for a successful blood substitute is that it be durable and versatile. The fact that "red blood" breaks down readily in the bloodstream shows that "red blood" is not durable in the bloodstream. This is the problem mentioned specifically in relation to "red blood", so choice (D) is the correct answer.



Due to ever-increasing paranoia about the transmission of hepatitis and AIDS via blood transfusions and the frequent difficulty of procuring matching blood donors for patients, researchers have been working at a feverish pace to produce disease-free and easy-to-use blood substitutes. The difficulty most synthetic blood researches have had is in formulating a substance that combines qualities of sterility, high capacity for carrying oxygen to body tissues, and versatility within the human body. Three major substitute technologies have been developed to date; each has certain advantages and shortcomings.
"Red blood," the first of the blood substitute technologies, is derived from hemoglobin which has been recycled from old, dead, or worn-out red blood cells and modified so that it can carry oxygen outside the red blood cell. Hemoglobin, a complex protein, is the blood's natural oxygen carrier and is attractive to scientists for use in synthetic blood because of its oxygen-carrying capacity. However, hemoglobin can sometimes constitute a two- fold threat to humans when it is extracted from the red blood cell and introduced to the body in its naked form. First, hemoglobin molecules are rarely sterile and often remain contaminated by viruses to which they were exposed in the cell. Second, naked hemoglobin is extremely dangerous to the kidneys, causing blood flow at these organs to shut down and leading, ultimately, to renal failure. Additional problems arise from the fact that hemoglobin is adapted to operate optimally within the intricate environment of the red blood cell. Stripped of the protection of the cell, the hemoglobin molecule tends to suffer breakdown within several hours. Although modification has produced more durable hemoglobin molecules which do not cause renal failure, undesired side effects continue to plague patients and hinder the development of hemoglobin-based blood substitutes.
Another synthetic blood alternative, "white blood", is dependent on laboratory synthesized chemicals called perfluorocarbons (PFCs). Unlike blood, PFCs are clear oil like liquids, yet they are capable of absorbing quantities of oxygen up to 50% of their volume, enough of an oxygen carrying potential for oxygen-dependent organisms to survive submerged in the liquid for hours by "breathing" it. Although PFCs imitate real blood by effectively absorbing oxygen, scientists are primarily interested in them as constituents of blood substitutes because they are inherently safer to use than hemoglobin-based substitutes. PFCs do not interact with any chemicals in the body and can be manufactured in near-perfect sterility. The primary pitfall of PFCs is in their tendency to form globules in plasma that can block circulation. Dissolving PFCs in solution can mitigate globulation; however, this procedure also seriously curtails the PFCs' oxygen capacity.
The final and perhaps most ambitious attempt to form a blood substitute involves the synthesis of a modified version of human hemoglobin by genetically-altered bacteria. Fortunately, this synthetic hemoglobin seems to closely mimic the qualities of sterility, and durability outside the cellular environment, and the oxygen-carrying efficiency of blood. Furthermore, researchers have found that if modified hemoglobin genes are added to bacterial DNA, the bacteria will produce the desired product in copious quantities. This procedure is extremely challenging, however, because it requires the isolation of the human gene for the production of hemoglobin, and the modification of the gene to express a molecule that works without support from a living cell.
While all the above technologies have serious drawbacks and difficulties, work to perfect an ideal blood substitute continues. Scientists hope that in the near future safe synthetic blood transfusions may ease blood shortages and resolve the unavailability of various blood types.
According to the passage, how much oxygen can be absorbed by a 300 cc sample of PFC?

  1. 50 cc
  2. 100 cc
  3. 150 cc
  4. 300 cc

Answer(s): C

Explanation:

This is an application question which requires you to apply information from the passage to solve a problem.
The passage mentions that PFCs are capable of absorbing quantities of oxygen up to 50% of their volume.
Applying this information, then, a 300 cc sample of PFC can absorb up to 150 cc, 50% of 300 cc. The correct answer, then, is choice (C), 150 cc.



Due to ever-increasing paranoia about the transmission of hepatitis and AIDS via blood transfusions and the frequent difficulty of procuring matching blood donors for patients, researchers have been working at a feverish pace to produce disease-free and easy-to-use blood substitutes. The difficulty most synthetic blood researches have had is in formulating a substance that combines qualities of sterility, high capacity for carrying oxygen to body tissues, and versatility within the human body. Three major substitute technologies have been developed to date; each has certain advantages and shortcomings.
"Red blood," the first of the blood substitute technologies, is derived from hemoglobin which has been recycled from old, dead, or worn-out red blood cells and modified so that it can carry oxygen outside the red blood cell. Hemoglobin, a complex protein, is the blood's natural oxygen carrier and is attractive to scientists for use in synthetic blood because of its oxygen-carrying capacity. However, hemoglobin can sometimes constitute a two- fold threat to humans when it is extracted from the red blood cell and introduced to the body in its naked form. First, hemoglobin molecules are rarely sterile and often remain contaminated by viruses to which they were exposed in the cell. Second, naked hemoglobin is extremely dangerous to the kidneys, causing blood flow at these organs to shut down and leading, ultimately, to renal failure. Additional problems arise from the fact that hemoglobin is adapted to operate optimally within the intricate environment of the red blood cell. Stripped of the protection of the cell, the hemoglobin molecule tends to suffer breakdown within several hours. Although modification has produced more durable hemoglobin molecules which do not cause renal failure, undesired side effects continue to plague patients and hinder the development of hemoglobin-based blood substitutes.
Another synthetic blood alternative, "white blood", is dependent on laboratory synthesized chemicals called perfluorocarbons (PFCs). Unlike blood, PFCs are clear oil like liquids, yet they are capable of absorbing quantities of oxygen up to 50% of their volume, enough of an oxygen carrying potential for oxygen-dependent organisms to survive submerged in the liquid for hours by "breathing" it. Although PFCs imitate real blood by effectively absorbing oxygen, scientists are primarily interested in them as constituents of blood substitutes because they are inherently safer to use than hemoglobin-based substitutes. PFCs do not interact with any chemicals in the body and can be manufactured in near-perfect sterility. The primary pitfall of PFCs is in their tendency to form globules in plasma that can block circulation. Dissolving PFCs in solution can mitigate globulation; however, this procedure also seriously curtails the PFCs' oxygen capacity.
The final and perhaps most ambitious attempt to form a blood substitute involves the synthesis of a modified version of human hemoglobin by genetically-altered bacteria. Fortunately, this synthetic hemoglobin seems to closely mimic the qualities of sterility, and durability outside the cellular environment, and the oxygen-carrying efficiency of blood. Furthermore, researchers have found that if modified hemoglobin genes are added to bacterial DNA, the bacteria will produce the desired product in copious quantities. This procedure is extremely challenging, however, because it requires the isolation of the human gene for the production of hemoglobin, and the modification of the gene to express a molecule that works without support from a living cell.
While all the above technologies have serious drawbacks and difficulties, work to perfect an ideal blood substitute continues. Scientists hope that in the near future safe synthetic blood transfusions may ease blood shortages and resolve the unavailability of various blood types.
It can be inferred from the passage that the difficulty of producing an ideal blood substitute is compounded by all of the following EXCEPT:

  1. there is no known way to isolate the DNA responsible for hemoglobin.
  2. naked hemoglobin tends to break down in the bloodstream.
  3. non-globulating PFCs have significantly abbreviated oxygen-carrying capacities.
  4. the use of PFCs may lead to blood clotting.

Answer(s): A

Explanation:

This is an inference question. It asks which of the answer choices is not a factor that detracts from the production of an ideal blood substitute. Choices (C) and (D) present troublesome aspects of PFCs. The end of the second paragraph establishes that one of the drawbacks of PFCs is that they form globules, blocking blood circulation, choice (D). In order to bypass this problem, scientists have attempted to modify PFCs so that they do not form globules. These efforts have been thwarted, however, as such modified PFCs have curtailed oxygen-carrying capacities, choice (C). Choice (B) relates to problems with "red blood". The third sentence of the second paragraph tells us that one of the problems of "red blood" is that its naked hemoglobin breaks down rapidly in the bloodstream. Choice (B), then, is a factor that has compounded the difficulty of producing an ideal blood substitute. Choice (A) presents a statement which, if supported by the passage, might very well compound the difficulties of producing an ideal synthetic blood. If there was no known way to isolate the DNA responsible for hemoglobin, then genetic engineering of modified hemoglobin, would be hampered.
But the passage never states that there is no known way to isolate the DNA responsible for hemoglobin. It does mention, in the last sentence of the fourth paragraph, that genetic engineering is challenging because it requires the isolation of the human gene for the production of hemoglobin. But the passage does not say that there is no known way to do this. Choice (A), therefore, is not suggested as a complication in the production of synthetic blood and is the correct answer.



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