Because natural selection acts against genes that cause inherited

Question

Because natural selection acts against genes that   cause inherited disorders, lethal genetic diseases should   be, and generally are, very rare. Thus it seems surprising   that certain inherited disorders of red blood cells,   notably sickle cell anemia and thalassemia, occur in   some populations at unusually high frequencies. We   have been able to explain this phenomenon through   natural selection by assuming that the same variant gene   that causes the lethal diseases in homozygous individuals   (who inherit two abnormal genes, one from each parent)   protects heterozygous individuals (who inherit one   abnormal and one normal gene) against another   potentially lethal, and more prevalent, disease—in this   case-malaria, which is produced by a parasite that infects   red blood cells. That protection maintains the high   frequencies of these otherwise deleterious genes.

The strength of malaria as a selective force derives from its powerful effects on the health and reproductive capacity of human populations. Malaria has been a major cause of death throughout history, contributing in Africa today to early-childhood mortality rates that are as high as 50 percent. It kills about 10 percent of its victims directly and contributes to the death of others by decreasing the ability of their immune systems to fight off other infections. Its high mortality rate ensures that a significant number of individuals will not live to reproduce; thus, any genetic mutation that provides resistance to malaria must have a high selective advantage.

That the sickle cell gene might confer such resistance was first indicated by the coincidence of the geographic ranges of sickle cell disease and malaria. Clinical evidence was harder to come by, but in 1954 Allison showed that children with the sickle cell gene had much milder cases of malaria than did children without it. Because the biochemical mechanism of this resistance to Malaria could not, however, be established, the role of the sickle-cell gene could not be unequivocally demonstrated.

This state of affairs persisted until 1977, when, after fifty years of attempts, a procedure was devised that allowed researchers to maintain malaria parasites in a laboratory culture. Using this technique, scientists could finally investigate how sickle cell blood cells protect a heterozygous carrier against malaria. They soon discovered that the parasite in an infected sickle cell develops normally up to the time that the cell is sequestered in tissue. There the low-oxygen environment and the low intracellular pH induce the characteristic sickling in the host cell, causing its potassium level to 'drop; this in turn causes the parasite to die. Such a process can protect against malaria even if not all of the parasites are affected because any meaningful reduction in the rate of multiplication of the parasite gives the immune system the time necessary to mount a protective response of its own.    1 
 1. The primary purpose of the passage is to

A. announce that the mechanism of sickle cell anemia has been discovered and to explain why the discovery was so difficult
B. explore the limits of natural selection and the way in which certain diseases can transcend them
C. describe how sickle cell anemia is produced and where it is most prevalent
D. explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed
E. analyze the effects of malaria on human populations and to suggest a way in which these effects can be minimized

2 
 2. According to the passage, which of the following is typically true of lethal genetic disorders?

A. They protect against some other lethal disease.
B. They are diseases of the red blood cells.
C. They have extremely low frequencies of occurrence.
D. They kill both homozygous and heterozygous individuals.
E. They occur only in certain geographical areas.

3 
 3. According to the passage, most malaria-related deaths occur

A. in areas only recently exposed to the disease
B. among young children
C. because of a mutation in the victim's genes
D. in individuals heterozygous for the sickle cell gene
E. because victims become more susceptible to other infections

4 
 4. It can be inferred from the passage that the number of individuals homozygous for the sickle cell gene is

A. approximately equal to the number who contract malaria
B. slightly smaller than the number who are heterozygous for the sickle cell gene
C. significantly smaller than the number who contract malaria
D. significantly larger than the number who are heterozygous for the sickle cell gene
E. Approximately equal to the number who die of malaria

5 
 5. According to the passage, the immediate cause of death of a malaria parasite in a red blood cell undergoing sickling is

A. a drop in the pH level of the cell
B. a drop in the potassium level of the cell
C. a drop in the oxygen content of the environment surrounding the cell
D. the sequestering of the cell in tissue
E. the protective response of the organism's immune system

6 
 6. The author suggests that in a lethal attack of malaria, which of the following occurs?

A. The intracellular pH drops much too slowly to induce sufficient sickling of red blood cells.
B. The malaria parasites spread much more rapidly than the host's immune system can respond.
C. Additional homozygous red blood cells are produced far more slowly than the malaria parasites spread.
D. The introduction of the malaria parasite prevents the host's immune system from responding.
E. The host's red blood cells art not sequestered in tissue in quantities sufficient to produce adequate supplies of sickled cells.

7 
 7. Which of the following best describes the organization of the first paragraph?

A. A generalization is presented and a seeming anomaly is reconciled with it.
B. A thesis is advanced and a counterexample is introduced to refute.
C. An argument is advanced and a general conclusion is derived from IL
D. An explanation is proposed and examined in
E. Opposing views are presented and their differences clarified.

8 
 8. Which of the following is most dearly an example of the way in which the majority of fatalities from malaria occur, as the process is described in the passage?

A. After an attack of malaria, the victim dies from a case of pneumonia.
B. Weakened from a case of the flu, the victim dies after contracting malaria.
C. The victim contracts malaria and dies shortly after exhibiting the first symptoms.
D. The victim inherits a blood disorder and quickly dies when infected with malaria.
E. The victim contracts malaria and, weakened by repeated bouts with it, eventually dies.

nivivacious · Answer

1. The primary purpose of the passage is to

A. announce that the mechanism of sickle cell anemia has been discovered and to explain why the discovery was so difficult 
 While discovery of the mechanism is mentioned in the third para, this is not the primary purpose of this passage

B. explore the limits of natural selection and the way in which certain diseases can transcend them 
 The passage does discuss natural selection and how sickle cell anemia persists despite it but it does not explore the limits of natural selection as a whole

C. describe how sickle cell anemia is produced and where it is most prevalent 
 It's more about the role of the sickle cell gene in providing resistance to malaria rather than the production or prevalence of sickle cell anemia

D. explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed
 This is correct. The passage primarily discusses the persistence of the sickle cell gene despite its detrimental effects, and how this persistence can be explained through its protective role against malaria. It also details how this theory was eventually confirmed through scientific research.

E. analyze the effects of malaria on human populations and to suggest a way in which these effects can be-minimized 
 The focus is more on the role of the sickle cell gene. While the passage does discuss the effects of malaria, it does not suggest ways to minimize these effects.

2. According to the passage, which of the following is typically true of lethal genetic disorders?

A. They protect against some other lethal disease. 
 This is not typically true for all lethal genetic disorders. The passage mentions this as a specific case, not as a general rule.

B. They are diseases of the red blood cells. 
 This is not necessarily true. The passage mentions anemia and thalassemia, which are diseases of the red blood cells, but it doesn't state that all lethal genetic disorders are diseases of red blood cells.

C. They have extremely low frequencies of occurrence.
This is correct. The passage states that "lethal genetic diseases should be, and generally are, very rare," which implies that they typically have extremely low frequencies of occurrence.

D. They kill both homozygous and heterozygous individuals. 
 This is not necessarily true. The passage mentions that the sickle cell gene causes lethal diseases in homozygous individuals, but it protects heterozygous individuals against malaria

E. They occur only in certain geographical areas. 
 This is not stated in the passage. While it mentions that sickle cell anemia and malaria coincide geographically, it doesn't claim this as a general rule for all lethal genetic disorders

3. According to the passage, most malaria-related deaths occur

A. in areas only recently exposed to the disease 
 The passage does not provide information to support this statement

B. among young children
The passage states, "Malaria has been a major cause of death throughout history, contributing is Africa today to early-childhood mortality rates that are as high as 50 percent." This suggests that a significant number of malaria-related deaths occur among young children

C. because of a mutation in the victim's genes 
 This is not stated in the passage

D. in individuals heterozygous for the sickle cell gene 
 Passage states the opposite that individuals heterozygous for the sickle cell gene are protected against malaria.

E. because victims become more susceptible to other infections 
 The passage does mention that malaria decreases the ability of the immune system to fight off other infections, contributing to the death of victims. However, it does not explicitly state that most malaria-related deaths occur for this reason.

4. It can be inferred from the passage that the number of individuals homozygous for the sickle cell gene is
 
 A. approximately equal to the number who contract malaria 
 There is nothing in the passage that supports this.

B. slightly smaller than the number who are heterozygous for the sickle cell gene 
 The passage does not provide specific information about the relative numbers of individuals who are homozygous versus heterozygous for the sickle cell gene.

C. significantly smaller than the number who contract malaria
The passage suggests that individuals homozygous for the sickle cell gene suffer from lethal diseases, while those heterozygous for the gene are protected against malaria. Given that malaria has high mortality rates and is prevalent, it can be inferred that the number of individuals contracting malaria is significantly larger than those homozygous for the sickle cell gene.

D. significantly larger than the number who art heterozygous for the sickle cell gene 
 There is nothing in the passage that supports this.

E. Approximately equal to the number who die of malaria 
 There is nothing in the passage that supports this.

5. According to the passage, the immediate cause of death of a malaria parasite in a red blood cell undergoing sickling is
 
 A. a drop in the pH level of the cell 
 The passage mentions a drop in pH as a condition that induces sickling but not as immediate cause of death

B. a drop in the potassium level of the cell
The passage states, "There the low-oxygen environment and the low intracellular pH induce the characteristic sickling in the host cell, causing its potassium level to 'drop; this in turn causes the parasite to die." This supports this answer.

C. a drop in the oxygen content of the environment surrounding the cell 
 This is mentioned but not as immediate cause of death

D. the sequestering of the cell in tissue 
 The passage does not state this as the cause of death

E. the protective response of the organism's immune system 
 The passage mentions the immune system's protective response as a result of the reduced multiplication rate of the parasite, not as the immediate cause of the parasite's death in a sickling cell.

6. The author suggests that in a lethal attack of malaria, which of the following occurs?
 
 A. The intracellular pH drops much too slowly to induce sufficient sickling of red blood cells.
 
 The passage does not provide information to support this statement.

B. The malaria parasites spread much more rapidly than the host's immune system can respond.
The passage states, "any meaningful reduction in the rate of multiplication of the parasite gives the immune system the time necessary to mount a protective response of its own." This suggests that in a lethal attack of malaria, the parasites spread faster than the immune system can respond

C. Additional homozygous red blood cells are produced far more slowly than the malaria parasites spread.
 
 The passage does not provide information to support this statement.

D. The introduction of the malaria parasite prevents the host's immune system from responding.
 
 The passage does not state that the introduction of the parasite prevents the immune system from responding. It suggests that the rapid spread of the parasite can outpace the immune response.

E. The host's red blood cells art not sequestered in tissue in quantities sufficient to produce adequate supplies of sickled cells 
 The passage does not provide information to support this statement.

7. Which of the following best describes the organization of the first paragraph?

A. A generalization is presented and a seeming anomaly is reconciled with it.
The first paragraph starts with a generalization about lethal genetic diseases being rare due to natural selection. It then presents an anomaly - the high frequency of certain inherited disorders like sickle cell anemia and thalassemia. The paragraph reconciles this anomaly with the generalization by explaining that these disorders provide protection against another lethal disease, malaria.

B. A thesis is advanced and a counterexample is introduced to refute. 
 The first paragraph does not introduce a counterexample to refute a thesis. Instead, it explains an anomaly in the context of a generalization.

C. An argument is advanced and a general conclusion is derived from IL 
 The first paragraph does not present an argument nor does it derive a general conclusion.

D. An explanation is proposed and examined in 
 This is not a clear description of the passage

E. Opposing views are presented and their differences clarified. 
 The first paragraph does not present opposing views.

8. Which of the following is most dearly an example of the way in which the majority of fatalities from malaria occur, as the process is described in the passage?

A. After an attack of malaria, the victim dies from a case of pneumonia.
The passage mentions that malaria contributes to the death of victims by decreasing the ability of their immune systems to fight off other infections. This suggests that a victim could die from another infection, such as pneumonia, after an attack of malaria.

B. Weakened from a case of the flu, the victim dies after contracting malaria. 
 Passage does not talk about this

C. The victim contracts malaria and dies shortly after exhibiting the first symptoms. 
 There is nothing in the passage that supports this

D. The victim inherits a blood disorder and quickly dies when infected with malaria. 
 Passage does not mention this. It mentions that individuals with certain blood disorders (like sickle cell anemia) have a protective advantage against malaria.

E. The victim contracts malaria and, weakened by repeated bouts with it, eventually dies. 
 While this could be a possible scenario, the passage specifically mentions the role of other infections in contributing to death after a malaria attack, which is more directly covered in option A

PK1 · Answer

Para 1: Author is explaining puzzling phenomenon of large presence of inherited disorders even though natural selection does not prefer or propagate inherited disorder. Uses malaria's absence, a lethal disease, while prevalence of sickle cell, a inherited disorder

Para 2: Explains why malaria was a lethal disease and provides advantage of other mutation to persist

Para 3: Proof was from area where both sickle cell and malaria was there. Observed that low cases of malaria while prevalent sickle cell. No biological proof though to unambiguously prove coincidence or correlation

Para 4: Malaria culture could help investigate the explanation. Further explains that malaria parasite remains till sickle cell develops. Once developed it kills malaria parasite and small population left can then acted by immune system.

Main Purpose: To explain puzzling phenomenon by giving the background and procedures that helped explain it meaningfully

1. The primary purpose of the passage is to

A. announce that the mechanism of sickle cell anemia has been discovered and to explain why the discovery was so difficult
--The last paragraph says malaria culture could investigate....and paragraph 3 and 4 does not discuss why discovery was so difficult.

B. explore the limits of natural selection and the way in which certain diseases can transcend them
-- Just focuses on Para 1 where it is discussed but it is not the purpose of the passage

C. describe how sickle cell anemia is produced and where it is most prevalent
-- Para 4 discussed how sickle cell is produced but does not say where it is most prevalent. It is also not the purpose of the passage

D. explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed
-- Passage is explaining why gene persisted and gives info around how this explanation was confirmed through parasite culture and coincidence of prevalence of sick cell with malaria
-- Purpose is aligned with author's thinking...para 1 says we have been able to explain... Para 4 says using malaria culture scientists could investigate. Para 3 says it was not established due to absence of biological proof.

This is the answer

E. analyze the effects of malaria on human populations and to suggest a way in which these effects can be-minimized
-- focuses on Para 2 where effect of malaria is discussed. It is no where discussed how the effects could be minimized.

2. According to the passage, which of the following is typically true of lethal genetic disorders?

A. They protect against some other lethal disease.
-- It is mentioned in Para 1 .." same variant gene that causes the lethal diseases in homozygous individuals protects heterozygous individuals against another potentially lethal, and more prevalent disease"

This is the answer

B. They are diseases of the red blood cells.
-- red blood cells are examples not that lethal genetic disorders are just diseases of red blood cells

C. They have extremely low frequencies of occurrence.
-- Puzzling phenomenon was related to abundance of some specific lethal genetic disorder examples

D. They kill both homozygous and heterozygous individuals.
-- It is not mentioned that they kill both type of individuals

E. They occur only in certain geographical areas.
-- Para 3 discussed a common area but it does not mean that such diseases occur in certain area only. Unsupported. Also usage of only is restricted while passage language is broader

3. According to the passage, most malaria-related deaths occur

A. in areas only recently exposed to the disease
-- unsupported as para 2 does not discuss about it. Also usage of only recently exposed restricts the scope

B. among young children
-- 50% death happens in early-childhood ...para 2 says "early-childhood mortality rates that are as high as 50 percent" but we do not know the population of young children as a a total and hence cannot directly conclude this

C. because of a mutation in the victim's genes
-- malaria provides a chance for gene to mutate to provide protection again it as discussed in para 2 and hence unsupported .."Its high mortality rate ensures that a significant number of individuals will not live to reproducer; thus, any genetic mutation that provides resistance to malaria must have a high selective advantage."

D. in individuals heterozygous for the sickle cell gene
--not supported as it is not talked about..infact para 1 says lethal genetic disorder in homzygous individuals protect heterozygous individuals against malaria type of diseases

E. because victims become more susceptible to other infections
-- Supported because in para 2 the sentence says "It kills about 10 percent of its victims directly and contributes to the death of others by decreasing the ability of their immune systems to fight off other infections"

This is the answer

4. It can be inferred from the passage that the number of individuals homozygous for the sickle cell gene is

..homozygous individual is one who has two abnormal genes obtained from each parent

A. approximately equal to the number who contract malaria
-- it means all homozygous contract malaria which is not supported

B. slightly smaller than the number who are heterozygous for the sickle cell gene
-- It is not mentioned in passage particularly para 1

C. significantly smaller than the number who contract malaria
-- It does not say homozygous individuals are smaller than one who contracts malaria

D. significantly larger than the number who are heterozygous for the sickle cell gene
-- homozygous protects heterozygous individuals and para 1 also says high frequency of deleterious genes " That protection maintains the high frequencies of these otherwise deleterious genes." hence it can only happen when homozygous is larger than heterozygous because homo has 2 genes and hetero has 1 deleterious gene

This is the answer

E. Approximately equal to the number who die of malaria
--it cannot be inferred from passage as homozygous protects against malaria

5. According to the passage, the immediate cause of death of a malaria parasite in a red blood cell undergoing sickling is

A. a drop in the pH level of the cell
-- "There the low-oxygen environment and the low intracellular pH induce the characteristic sickling in the host cell, causing its potassium level to 'drop.this in turn causes the parasite to die" so both drop in ph level and oxygen is required. Not supported

B. a drop in the potassium level of the cell
-- Para 4 supports this... that drop in potassium level causes parasite to die...."There the low-oxygen environment and the low intracellular pH induce the characteristic sickling in the host cell, causing its potassium level to 'drop.this in turn causes the parasite to die"

This is the answer

C. a drop in the oxygen content of the environment surrounding the cell
-- Similar to option A it just talks about one condition not both ( low oxygen and low pH)

D. the sequestering of the cell in tissue
--it says malaria parasite develops normally upto the time of sequestering of cell in tissue but does not tie to parasite. thereafter it may develop not normally . Then low ph and low oxygen is required for sickling in host cell..

E. the protective response of the organism's immune system
---protective response of immune system is to fight against residual parasite not for immediate death..."Such a process can protect against malaria even if not all of the parasites are affected because any meaningful reduction in the rate of multiplication of the parasite gives the immune system the time necessary to mount a protective response of its own"

6. The author suggests that in a lethal attack of malaria, which of the following occurs?

A. The intracellular pH drops much too slowly to induce sufficient sickling of red blood cells.
-- Para 4 does not say that pH drop much slowly in case of lethal attach of malaria

B. The malaria parasites spread much more rapidly than the host's immune system can respond.
-- Para 4 says that there is a meaningful reduction in the rate of multiplication of the parasite from sickle cell hence without sickle cell we can infer that it spreads more rapidly than immune system can respond

This is the answer

C. Additional homozygous red blood cells are produced far more slowly than the malaria parasites spread.
--It does not say that additional homozygous red blood cell or sickle cell is produced slowly

D. The introduction of the malaria parasite prevents the host's immune system from responding.
-- It does not say that it prevents immune system to respond. It says multiplicative nature of parasite is not interrupted or responded properly by immune system

E. The host's red blood cells art not sequestered in tissue in quantities sufficient to produce adequate supplies of sickled cells
-- It is not discussed in para 4 of the passage in case of lethal attack of malaria

7. Which of the following best describes the organization of the first paragraph?

A. A generalization is presented and a seeming anomaly is reconciled with it.
-- First part is good but no anomaly is reconciled in the passage..

B. A thesis is advanced and a counterexample is introduced to refute.
-- A thesis in form of possible explanation was given but no counterexample is introduced

C. An argument is advanced and a general conclusion is derived from IL
-- An argument in form of possible explanation is given but no general conclusion is derived ...it is not the flow of passage

D. An explanation is proposed and examined in
-- Para 1 provides explanation and further examined through malaria prevalence at places which give rise to genetic disorder and then area where one is prevalent and other is absent. Para 4 further provides biological evidence

This is the answer

E. Opposing views are presented and their differences clarified
-- There is no opposing views and differences clarified. It just author's view and further explanation of evidence biologically in para 4 following para 3.

8. Which of the following is most dearly an example of the way in which the majority of fatalities from malaria occur, as the process is described in the passage?

A. After an attack of malaria, the victim dies from a case of pneumonia.
-- Immune system's ability to fight other infections is decreased, leading to death. so here pneumonia acts as other infection and is the answer

This is answer

B. Weakened from a case of the flu, the victim dies after contracting malaria.
-- It says cause is flu and then victim dies and hence unsupported

C. The victim contracts malaria and dies shortly after exhibiting the first symptoms.
-- Not supported...it does not say that victim dies after his/her first symptoms

D. The victim inherits a blood disorder and quickly dies when infected with malaria.
-- Not supported..it says first blood disorder and then dies ...infact the article is about blood disorder such as sickle cell protecting against malaria

E. The victim contracts malaria and, weakened by repeated bouts with it, eventually dies.
-- It does not say that repeated bout weaken and then it dies. Immune system's ability to fight other infections is decreased, leading to death.

Shadyshades · Answer

1. The primary purpose of the passage is to

A. announce that the mechanism of sickle cell anemia  has been discovered  and to explain why the discovery was so difficult- Incorrect.  The discovery happened way back in 70s. I am going to eliminate the option based on the tenses.  
B.  explore the limits of natural selection and the way in which certain diseases can transcend them - Incorrect.  The author doesn't explore the limits of natural selection. Moreover, the author talks about only a specific type of disease and not "certain   diseases ". 
C. describe how sickle cell anemia is produced and where it is most prevalent-Incorrect. The passage is not primarily concerned about how sickle cell anemia is produced but rather how such cell protects other prevalent diseases. 
  D. explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed.   Correct. 
E.  analyze the effects of malaria on human populations and to suggest a way in which these effects can be-minimized - Incorrect.  In the passage, there is no intentional way to minimize the effects of Malaria. It genetically happens.

2. According to the passage, which of the following is typically true of lethal genetic disorders?

A.  They protect against some other lethal disease .- Tricky but incorrect. Refer to the lines-  the same variant gene that causes the lethal diseases in homozygous individuals protects heterozygous individuals against another  potentially lethal , and more prevalent disease  . It's not lethal but potentially lethal disease. 
B.   They are diseases of the red blood cells  .- Not sure whether LGD are the disease of RBC mean the same as LGD inherited the disease of RBC. Probably or probably not. Either way, I am going to hold on to this. 
C.  They have extremely low frequencies of occurrence . - Incorrect. Though they occur in some part of the population, Lethal genetic disorders have high frequencies of occurrence. 
D.  They kill both homozygous and heterozygous individuals.  – Incorrect. Refer to the lines-  The same variant gene that causes the lethal diseases in homozygous individuals protects heterozygous individuals against another potentially lethal.  
E.  They occur only in certain geographical areas .- Incorrect. It’s mentioned that LGD occur in some population. The population is small but can be from Asia, Europe or Africa. It doesn’t have to be from a specific zone.

3. According to the passage, most malaria-related deaths occur

A. in areas  only recently exposed  to the disease-Incorrect. Refer-  Malaria has been   a major cause of death throughout history  , contributing is Africa today to early-childhood mortality rates that are as high as 50 percent 
B.  among young children - Refer to above mentioned lines. The passage says that the mortality of early childhood are as high as 50% but it never states that the majority of malaria related death occurs among young children.
C.  because of a mutation in the victim's genes - Incorrect. Mutation can actually help to curb Malaria related deaths. Refer to the lines-  any genetic mutation that provides resistance to malaria must have a high selective advantage. 
D.  in individuals heterozygous for the sickle cell gene - Incorrect. We don't expect Malaria related deaths in heterozygous individuals at least as the LGD protects such individuals. Refer to the lines-  the same variant gene that causes the lethal diseases in homozygous individuals protects heterozygous individuals against another potentially lethal, and more prevalent disease  You can also refer-  scientists could finally investigate how sickle cell blood cells protect a heterozygous carrier against malaria 
E.   because victims become more susceptible to other infections  - Correct. Refer to the lines-   It kills about 10 percent of its victims directly and  contributes to the death of others  (rest 90%)  by decreasing the ability of their immune systems to fight off other infections .

4. It can be inferred from the passage that the number of individuals homozygous for the sickle cell gene is

This is the most annoying question I find in the passage. Honestly, I am just following my gut feeling here and based on the below lines, I am marking option D as the number of individuals in homozygous will be twice the individuals in heterozygous   
 We have been able to explain this phenomenon through natural selection by assuming that the same variant gene that causes the lethal diseases in homozygous individuals   (who inherit two abnormal genes, one from each parent)   protects heterozygous individuals (  who inherit one abnormal and one normal gene  )

A. approximately equal to the number who contract malaria
B. slightly smaller than the number who are heterozygous for the sickle cell gene
C. significantly smaller than the number who contract malaria
  D. significantly larger than the number who art heterozygous for the sickle cell gene  
E. Approximately equal to the number who die of malaria

5. According to the passage, the immediate cause of death of a malaria parasite in a red blood cell undergoing sickling is

A. a drop in the pH level of the cell
B. a drop in the potassium level of the cell
  C. a drop in the oxygen content of the environment surrounding the cell  
D. the sequestering of the cell in tissue
E. the protective response of the organism's immune system

Refer to the lines-  They (Scientists) soon discovered that the parasite in an infected sickle cell develops normally up to the time that the cell is sequestered in tissue. There the low-oxygen environment and the low intracellular pH induce the characteristic sickling in the host cell,  causing its potassium level to 'drop;  this in turn causes the parasite to die

The immediate cause of death is a drop in O2 content. Option C is a correct answer.

6. The author suggests that in a lethal attack of malaria, which of the following occurs?

A.  The intracellular pH drops much too slowly to induce sufficient sickling of red blood cells . - Incorrect. pH drop will actually help to kill the parasite and will not make malaria a lethal attacker. 
B.   The malaria parasites spread much more rapidly than the host's immune system can respond.  - Correct. 
C. Additional homozygous red blood cells are produced far more slowly than the malaria parasites spread.- Incorrect.  It's nowhere mentioned in the passage.  
D. The introduction of the malaria parasite prevents the host's immune system from responding.- Incorrect.  Malaria parasite actually slows and weakens the immune system to respond. Malaria doesn't totally prevent immune system to respond. System responds but way too slowly and bleakly.  
E.  The host's red blood cells art not sequestered in tissue in quantities sufficient to produce adequate supplies of sickled cells. - Incorrect. Refer-  They soon discovered that the parasite in an infected sickle cell develops normally up to the time that the cell is sequestered in tissue

7. Which of the following best describes the organization of the first paragraph?

A. A generalization is presented and a seeming anomaly is reconciled with it. 
B. A thesis is advanced and a counterexample is introduced to refute.
C. An argument is advanced and a general conclusion is derived from IL
D. An explanation is proposed and examined in
E. Opposing views are presented and their differences clarified.

The author in the first para mentioned that  
 the same variant gene that causes the lethal diseases in homozygous individuals protects heterozygous individuals against another potentially lethal, and more prevalent disease—in this case-malaria, which is produced by a parasite that infects red blood cells. That protection maintains the high frequencies of these otherwise deleterious genes.

Means, an explanation is proposed.

...and in rest of the para, the author tries to examine how such protection occurs against potentially lethal and prevalent disease.

Option D is the correct answer.

A.  A generalization is presented and a seeming anomaly is reconciled with it .- The author mentions an anomaly but doesn't reconcile till the end. 
B.  A thesis is advanced and a counterexample is introduced to refute .- There is no counterexample that is introduced to refute. 
C.  An argument is advanced and a general conclusion is derived from IL . It's more of a examination than a conclusion. 
E.  Opposing views are presented and their differences clarified .- No opposing views are presented in the passage.

8. Which of the following is most dearly an example of the way in which the majority of fatalities from malaria occur, as the process is described in the passage?

A. After an attack of malaria, the victim dies from a case of pneumonia.
B. Weakened from a case of the flu, the victim dies after contracting malaria.
C. The victim contracts malaria and dies shortly after exhibiting the first symptoms.
D. The victim inherits a blood disorder and quickly dies when infected with malaria.
E. The victim contracts malaria and, weakened by repeated bouts with it, eventually dies.

Refer to the lines-   It kills about 10 percent of its victims directly and contributes to the death of others by decreasing the ability of their immune systems to fight off other infections.  
  Means, Malaria will weaken immune system of a person, thus it will reduce the ability to fight other infections such as flu, Typhoid etc. and eventually the person dies.

A.   After an attack of malaria, the victim dies from a case of pneumonia . - It resembles what we just said in above lines. Hold ON.
B.  Weakened from a case of the flu, the victim dies after contracting malaria .- Incorrect. One will be weakened by malaria not by other infections and one will die by other infections after contracting Malaria. 
C.  The victim contracts malaria and dies shortly after exhibiting the first symptoms. - Nop, The first symptoms will only be brutal to 10% of the victims. 
D.  The victim inherits a blood disorder and quickly dies when infected with malaria .- If a victim dies quickly, he or she will fall under 10% of population and not majority of population (as asked in the question).
E.  The victim contracts malaria and, weakened by repeated bouts with it, eventually dies.  Partially correct. There is nothing mentioned about other infections here. We need that to support author's view.

Catman · Answer

1. The primary purpose of the passage is to 
Passage Summary-> A general anamoly is discused and resolved by giving explanation for it's occurence. "Why the sickle cell disease, caused by inherited disorder of Red Blood Cells (RBC), should be a rare disease as natural selection acts against them. But this is not true, since these genes provides resistance to the another RBC disease Malaria and thus reoccur despite natural selection of genes acting against them. " This facts removes the anomaly that why the Sickle disease despite a rare disease is occurring at unusually high frequencies.

A. announce that the mechanism of sickle cell anemia has been discovered and to explain why the discovery was so difficult  ~ Incorrect, The passage is related to the genes that causes Sickle cell disease. 
B. explore the limits of natural selection and the way in which certain diseases can transcend them  ~ The passage is not exploring the limit of natural selection. 
C. describe how sickle cell anemia is produced and where it is most prevalent  ~Although sickle cell prevalence is discussed, how it is produced is out of scope. 
D. explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed  ~ Correct as per the above analysis. 
E. analyze the effects of malaria on human populations and to suggest a way in which these effects can be-minimized  ~ Incorrect, passage is about the genes related to the sickle cell disease and not about Malaria.

2. According to the passage, which of the following is typically true of lethal genetic disorders? 
Refer to the line -> "We have been able to explain this phenomenon through natural selection by assuming that the same variant gene that causes the lethal diseases in homozygous individuals (who inherit two abnormal genes, one from each parent) protects heterozygous individuals (who inherit one abnormal and one normal gene) against another potentially lethal, and more prevalent disease—in this case-malaria,"

A. They protect against some other lethal disease. 
B. They are diseases of the red blood cells.
C. They have extremely low frequencies of occurrence.
D. They kill both homozygous and heterozygous individuals.
E. They occur only in certain geographical areas.

3. According to the passage, most malaria-related deaths occur 
Refer to the line -> It kills about 10 percent of its victims directly and contributes to the death of others by decreasing the ability of their immune systems to fight off other infections.

A. in areas only recently exposed to the disease
B. among young children
C. because of a mutation in the victim's genes
D. in individuals heterozygous for the sickle cell gene
 E. because victims become more susceptible to other infections

4. It can be inferred from the passage that the number of individuals homozygous for the sickle cell gene is 
Malaria can occur to both normal genes. 
Malaria can also occur to one abnormal one normal genes(heterozygous individuals)
These heterozygous are protected by Malaria from homozygous individuals( who have 2 abnormal genes). 
Homozygous individuals may or may not be susceptible to malaria.

A. approximately equal to the number who contract malaria  ~ Based on the above information, this cannot be true. 
B. slightly smaller than the number who are heterozygous for the sickle cell gene  ~ Based on the above information, this cannot be true. 
C. significantly smaller than the number who contract malaria  ~ Based on the above information, this cannot be true. 
 D. significantly larger than the number who art heterozygous for the sickle cell gene 
E. Approximately equal to the number who die of malaria  ~ Homozygous genes prevents Heterozygous from Malaria.

5. According to the passage, the immediate cause of death of a malaria parasite in a red blood cell undergoing sickling is 
Refer to the line "There the low-oxygen environment and the low intracellular pH induce the characteristic sickling in the host cell, causing its potassium level to 'drop; this in turn causes the parasite to die."
Immediate effect-> Drop in potassium level of the cell. Choice B.

A. a drop in the pH level of the cell
 B. a drop in the potassium level of the cell 
C. a drop in the oxygen content of the environment surrounding the cell
D. the sequestering of the cell in tissue
E. the protective response of the organism's immune system

6. The author suggests that in a lethal attack of malaria, which of the following occurs? 
Refer to the line"Such a process can protect against malaria even if not all of the parasites are affected because any meaningful reduction in the rate of multiplication of the parasite gives the immune system the time necessary to mount a protective response of its own."

A. The intracellular pH drops much too slowly to induce sufficient sickling of red blood cells.   ~ This is only true for people who have sickle cell disease. 
 B. The malaria parasites spread much more rapidly than the host's immune system can respond. 
C. Additional homozygous red blood cells are produced far more slowly than the malaria parasites spread.  ~ Additional red blood cells are produced slowly due to the slow response of the immune system against Malaria 
D. The introduction of the malaria parasite prevents the host's immune system from responding.  ~ Immune system is slow in responding and not stopped from responding. 
E. The host's red blood cells art not sequestered in tissue in quantities sufficient to produce adequate supplies of sickled cells.  ~This is a specific case for the people who have sickle cell disease.

7. Which of the following best describes the organization of the first paragraph? 
A general perception is mentioned that Lethal Genetics Disease should be rare. But it is contested that this general perception is not true and explanation for the same is given by the author in the first paragraph.Choice A.

A. A generalization is presented and a seeming anomaly is reconciled with it. 
B. A thesis is advanced and a counterexample is introduced to refute.
C. An argument is advanced and a general conclusion is derived from it
D. An explanation is proposed and examined in
E. Opposing views are presented and their differences clarified.

8. Which of the following is most dearly an example of the way in which the majority of fatalities from malaria occur, as the process is described in the passage? 
Refer to the line "It kills about 10 percent of its victims directly and contributes to the death of others by decreasing the ability of their immune systems to fight off other infections."

A. After an attack of malaria, the victim dies from a case of pneumonia.  After Malaria immune system is weakened and new infection (pneumonia) cannot be fought off leading to the death of victim. 
B. Weakened from a case of the flu, the victim dies after contracting malaria.  ~ Immune system is first weakened by Malaria and than it is not able to fight other infections such as the Flu. 
C. The victim contracts malaria and dies shortly after exhibiting the first symptoms. ~ It is only for the 10% of the cases. 
D. The victim inherits a blood disorder and quickly dies when infected with malaria. ~ Only, the victim immune system is weakened by malaria , he does not inherits any blood disorder. 
E. The victim contracts malaria and, weakened by repeated bouts with it, eventually dies.  ~ Immune system is weakened to fight off the other infections. Malaria is the same infection.

0Lucky0 · Answer

B, C, E, D, B, B, A, A.

1. The primary purpose of the passage is to

A. announce that the mechanism of sickle cell anemia has been discovered and to explain why the discovery was so difficult -->This is good but the paragraph doesn't say it was difficult.
  B. explore the limits of natural selection and the way in which certain diseases can transcend them   -->This is the right answer. The paragraph does show this.
C. describe how sickle cell anemia is produced and where it is most prevalent -->The paragraph does talk about this but it wasn't the primary purpose of the passage.
D. explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed -->Again, this is talked about but it wasn't the primary purpose.
E. analyze the effects of malaria on human populations and to suggest a way in which these effects can be-minimized -->Out of scope.

2. According to the passage, which of the following is typically true of lethal genetic disorders?

A. They protect against some other lethal disease. -->This makes no sense.
B. They are diseases of the red blood cells. -->Not mentioned.
  C. They have extremely low frequencies of occurrence.   -->The paragraph does talk about this.
D. They kill both homozygous and heterozygous individuals. -->Incorrect.
E. They occur only in certain geographical areas. -->Not true.

3. According to the passage, most malaria-related deaths occur

A. in areas only recently exposed to the disease -->Not mentioned.
B. among young children -->Not true.
C. because of a mutation in the victim's genes -->Incorrect..
D. in individuals heterozygous for the sickle cell gene -->Not mentioned.
  E. because victims become more susceptible to other infections   -->True, this is mentioned in the passage.

4. It can be inferred from the passage that the number of individuals homozygous for the sickle cell gene is

A. approximately equal to the number who contract malaria -->not correct.
B. slightly smaller than the number who are heterozygous for the sickle cell gene -->This is not mentioned.
C. significantly smaller than the number who contract malaria -->incorrect.
 D. significantly larger than the number who art heterozygous for the sickle cell gene  -->This is true.
E. Approximately equal to the number who die of malaria -->out of scope

5. According to the passage, the immediate cause of death of a malaria parasite in a red blood cell undergoing sickling is

A. a drop in the pH level of the cell -->This is not the reason.
  B. a drop in the potassium level of the cell   -->correct. This is mentioned.
C. a drop in the oxygen content of the environment surrounding the cell -->This is not the reason either.
D. the sequestering of the cell in tissue -->Incorrect.
E. the protective response of the organism's immune system -->Out of scope.

6. The author suggests that in a lethal attack of malaria, which of the following occurs?

A. The intracellular pH drops much too slowly to induce sufficient sickling of red blood cells. -->Nowhere is this mentioned.
  B. The malaria parasites spread much more rapidly than the host's immune system can respond.   -->Correct. This is mentioned.
C. Additional homozygous red blood cells are produced far more slowly than the malaria parasites spread. -->Incorrect.
D. The introduction of the malaria parasite prevents the host's immune system from responding. -->This is not mentioned anywhere.
E. The host's red blood cells art not sequestered in tissue in quantities sufficient to produce adequate supplies of sickled cells. -->Out of scope.

7. Which of the following best describes the organization of the first paragraph?

A. A generalization is presented and a seeming anomaly is reconciled with it.   -->True, this is the case.
B. A thesis is advanced and a counterexample is introduced to refute. -->There is no thesis.
C. An argument is advanced and a general conclusion is derived from IL -->This is incorrect.
D. An explanation is proposed and examined in -->There is no examination.
E. Opposing views are presented and their differences clarified. -->This is not the case.

8. Which of the following is most dearly an example of the way in which the majority of fatalities from malaria occur, as the process is described in the passage?

A. After an attack of malaria, the victim dies from a case of pneumonia. /color] -->Correct.
B. Weakened from a case of the flu, the victim dies after contracting malaria. -->This isn't right.
C. The victim contracts malaria and dies shortly after exhibiting the first symptoms. -->We can't assume this.
D. The victim inherits a blood disorder and quickly dies when infected with malaria. -->This can't be concluded.
E. The victim contracts malaria and, weakened by repeated bouts with it, eventually dies. -->Incorrect.

B, C, E, D, B, B, A, A.

pintukr · Answer

1. The primary purpose of the passage is to

A. announce that the mechanism of sickle cell anemia has been discovered and to explain why the discovery was so difficult
 too limited in scope to highlight the primary purpose

B. explore the limits of natural selection and the way in which certain diseases can transcend them
 purpose achieved through the exemplification of malaria

C. describe how sickle cell anemia is produced and where it is most prevalent
 sickle cell anemia has been used to explain the underlying theme of certain diseases transcend the limits of natural selection

D. explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed
 persistence of the gene used as a premise to reach the conclusion

E. analyze the effects of malaria on human populations and to suggest a way in which these effects can be-minimized
 out of scope --- not covered in the passage

2. According to the passage, which of the following is typically true of lethal genetic disorders?

A. They protect against some other lethal disease.
 distortion; not highlighted that for all lethal disorders protect against some other lethal disease

B. They are diseases of the red blood cells.
 one example can't generalize that lethal genetic disorders are diseases of the red blood cells

C. They have extremely low frequencies of occurrence.
 'Because natural selection acts against genes that cause inherited disorders, lethal genetic diseases should be, and generally are, very rare'

D. They kill both homozygous and heterozygous individuals.
 lethal genetic disorders causes the lethal diseases in homozygous individuals; while protecting heterozygous individuals against another potentially lethal, and more prevalent disease

E. They occur only in certain geographical areas.
 no such claims made in the passage

3. According to the passage, most malaria-related deaths occur

A. in areas only recently exposed to the disease
 deaths not related to specific areas

B. among young children
 not true as per the passage

C. because of a mutation in the victim's genes
 mutation in genes not discussed

D. in individuals heterozygous for the sickle cell gene
 opposite to this ie, homozygous will be true

E. because victims become more susceptible to other infections
 susceptibility to other infections -- has been cited as reason for most deaths

4. It can be inferred from the passage that the number of individuals homozygous for the sickle cell gene is

A. approximately equal to the number who contract malaria
 not verified using the facts in the passage
 
B. slightly smaller than the number who are heterozygous for the sickle cell gene
 no such deductions using facts presented in the passage

C. significantly smaller than the number who contract malaria
 not true as per the passage

D. significantly larger than the number who are heterozygous for the sickle cell gene
 comparison of numbers of individuals not drawn in the passage

E. Approximately equal to the number who die of malaria
  individuals (homozygous) susceptible to death -- not protected owing to 'both' abnormal genes

5. According to the passage, the immediate cause of death of a malaria parasite in a red blood cell undergoing sickling is

A. a drop in the pH level of the cell
 not true as per the passage
 
B. a drop in the potassium level of the cell
 drop in the potassium level of the cell -- clearly highlighted in the 4th paragraph as the immediate cause of death of a malaria parasite

C. a drop in the oxygen content of the environment surrounding the cell
 not true as per the passage
 
D. the sequestering of the cell in tissue
 not true as per the passage

E. the protective response of the organism's immune system
 not the cause of death of a malaria parasite in a red blood cell undergoing sickling

6. The author suggests that in a lethal attack of malaria, which of the following occurs?

A. The intracellular pH drops much too slowly to induce sufficient sickling of red blood cells.
  intracellular pH drops -- not supported by the passage
 
B. The malaria parasites spread much more rapidly than the host's immune system can respond.
 can be inferred using the facts presented in the last few lines of last paragraph -- the immune system doesn't get the time necessary to mount a protective response of its own.

C. Additional homozygous red blood cells are produced far more slowly than the malaria parasites spread.
 no such facts presented in the passage

D. The introduction of the malaria parasite prevents the host's immune system from responding.
 host's immune system response is slow, not totally absent

E. The host's red blood cells art not sequestered in tissue in quantities sufficient to produce adequate supplies of sickled cells.
 Out of scope -- sufficiency of quantities not discussed in the passage

7. Which of the following best describes the organization of the first paragraph?

A. A generalization is presented and a seeming anomaly is reconciled with it.
 generalization (first half) -- natural selection acts against genes that cause inherited disorders, lethal genetic diseases should be, and generally are, very rare; a seeming anomaly is reconciled (second half) -- ...That protection maintains the high frequencies of these otherwise deleterious genes.

B. A thesis is advanced and a counterexample is introduced to refute.
 thesis is not refuted using the example of malaria

C. An argument is advanced and a general conclusion is derived from it
 no conclusions drawn in he 1st paragraph

D. An explanation is proposed and examined in detail
 covers only the 2nd half of the first paragraph
 
E. Opposing views are presented and their differences clarified.
 Irrelevant -- views presented are not opposing each other

8. Which of the following is most dearly an example of the way in which the majority of fatalities from malaria occur, as the process is described in the passage?

A. After an attack of malaria, the victim dies from a case of pneumonia.
Out of scope -- pneumonia not the reason for the majority of fatalities

B. Weakened from a case of the flu, the victim dies after contracting malaria.
 'flu' not discussed in the passage

C. The victim contracts malaria and dies shortly after exhibiting the first symptoms.
 no such facts regarding sudden death presented in the passage

D. The victim inherits a blood disorder and quickly dies when infected with malaria.
 inheritance of blood disorder leads to slow immune response , eventually leading to the death of the victim

E. The victim contracts malaria and, weakened by repeated bouts with it, eventually dies.
 weakened / slow immune response -- the stimulus can be inferred

BCEEBBAE is the correct answer sequence

Sajjad1994 · Answer

Official Explanation

1. The primary purpose of the passage is to

Explanation

(A)  While the passage mentions the difficulty in understanding the mechanism of sickle cell anemia, the main focus is on explaining why the gene for sickle cell anemia has persisted and how this explanation was confirmed.

(B)  Although the passage discusses natural selection and its role in the persistence of the sickle cell gene, it does not explore the limits of natural selection or discuss how diseases can transcend them in a broader context.

(C)  While the passage briefly mentions sickle cell anemia, it does not focus on describing how it is produced or where it is most prevalent. Its main emphasis is on the relationship between the sickle cell gene and malaria resistance.

(D)  This is correct!   The passage discusses the persistence of the sickle cell gene in certain populations despite its association with a lethal genetic disease. It explains that the high frequency of this gene can be attributed to its protective effect against malaria. It also describes the historical context of attempts to understand this phenomenon and how, in 1977, a breakthrough allowed researchers to confirm the mechanism by which sickle cell blood cells protect against malaria.

(E)  While the passage mentions the effects of malaria on human populations, it does not primarily focus on analyzing these effects or suggesting ways to minimize them. Its central focus is on analyzing these effects or suggesting ways to minimize them. Its central focus is on the genetic relationship between sickle cell anemia and malaria resistance.

Answer: D

Sajjad1994 · Answer

Official Explanation

2. According to the passage, which of the following is typically true of lethal genetic disorders?

Explanation

(A)  This is typically true of the discussed lethal genetic disorders, such as sickle cell anemia and thalassemia. The passage explains that these disorders, which are normally lethal when homozygous (two abnormal genes), actually protect heterozygous individuals (one abnormal and one normal gene) against another potentially lethal disease, malaria.

(B)  This is not necessarily true of all lethal genetic disorders. While the passage discusses lethal genetic disorders of red blood cells, it does not claim that this is a universal characteristic of lethal genetic disorders. Lethal genetic disorders can affect various systems and organs in the body.

(C)  This is correct!   The passage explains that natural selection tends to act against genes that cause inherited disorders, which is why lethal genetic diseases should generally be very rare. In contrast, the passage discusses certain inherited disorders of red blood cells, such as sickle cell anemia and thalassemia, which occur in some populations at unusually high frequencies. This is presented as surprising and is explained by the fact that the same variant gene that causes these lethal diseases in homozygous individuals (who inherit two abnormal genes) actually protects heterozygous individuals (who inherit one abnormal and one normal gene) against another potentially lethal disease, malaria. So, these disorders are an exception to the rule and have high frequencies due to their protective effect against malaria.

(D)  This is typically true of lethal genetic disorders, as they are generally lethal when an individual inherits two abnormal genes (homozygous) and can cause severe health problems or death in individuals with one abnormal gene (heterozygous).

(E)  This is not a characteristic typically mentioned in the passage regarding lethal genetic disorders. The passage primarily focuses on the rarity of lethal genetic disorders due to natural selection and their relationship with malaria resistance, rather than their geographical distribution.

Answer: C

Sajjad1994 · Answer

Official Explanation

3. According to the passage, most malaria-related deaths occur

Explanation

(A)  The passage does not provide information about the timing of exposure to malaria in different areas. It focuses on the impact of malaria on human populations and how certain genetic factors, like the sickle cell gene, play a role in malaria resistance. Therefore, this option is not supported by the passage.

(B)  The passage does mention that malaria contributes to early childhood mortality rates, but it does not exclusively state that most malaria-related deaths occur among young children. It discusses malaria as a major cause of death throughout history, but it does not specify the age group most affected.

(C)  The passage does discuss genetic factors related to malaria resistance, such as the sickle cell gene. However, it does not attribute most malaria-related deaths to a mutation in the victim's genes. Instead, it emphasizes the impact of malaria on the immune system and its role in making individuals more susceptible to other infections.

(D)  The passage does mention the role of the sickle cell gene in conferring resistance to malaria, but it does not specify that most malaria-related deaths occur in individuals heterozygous for this gene. It discusses the protective effect of the sickle cell gene against malaria but does not provide data on the frequency of malaria-related deaths in this specific genetic group.

(E)  This is correct!   The passage mentions that malaria contributes to the death of some individuals not only by directly killing about 10 percent of its victims but also by decreasing the ability of their immune systems to fight off other infections. This weakened immune response to other infections is what leads to additional deaths, making individuals more susceptible to diseases other than malaria.

Answer: E

Sajjad1994 · Answer

Official Explanation

4. It can be inferred from the passage that the number of individuals homozygous for the sickle cell gene is

Explanation

(A)  The passage does not provide information about the exact numerical relationship between individuals homozygous for the sickle cell gene and the number of people who contract malaria. It does mention that the sickle cell gene is more prevalent in populations where malaria is common, but it doesn't suggest that these numbers are approximately equal.

(B)  The passage discusses the protective effect of the sickle cell gene in heterozygous individuals against malaria, but it doesn't provide information about the relative numbers of homozygous and heterozygous individuals in the population.

(C)  This is correct!   The passage explains that the sickle cell gene, when homozygous (two abnormal genes), causes the lethal disease sickle cell anemia. However, it also mentions that the sickle cell gene is maintained in the population because it protects heterozygous individuals (one abnormal and one normal gene) against malaria. Since the sickle cell gene is maintained due to its protective effect against malaria, it implies that the number of individuals homozygous for the sickle cell gene (who have two abnormal genes) is significantly smaller than the number who contract malaria. If the number of homozygous individuals were larger, the gene would be less rare in the population, and it wouldn't be maintained through natural selection.

(D)  It actually suggests the opposite, as it discusses that the sickle cell gene is maintained due to its protective effect against malaria in heterozygous individuals, implying that the number of homozygous individuals is likely smaller than heterozygous individuals.

(E)  While the passage discusses the impact of malaria on mortality rates, it does not give specific numbers or ratios of individuals homozygous for the sickle cell gene to the number who die of malaria. Therefore, it is not possible to conclude that these numbers are approximately equal based solely on the information in the passage.

Answer: C

Sajjad1994 · Answer

Official Explanation

5. According to the passage, the immediate cause of death of a malaria parasite in a red blood cell undergoing sickling is

Explanation

(A)  This is not the immediate cause of death of the malaria parasite in a red blood cell undergoing sickling, as per the passage. While it is mentioned that the low intracellular pH is involved in inducing the characteristic sickling of the host cell, the drop in pH alone is not stated to be the direct cause of the parasite's death.

(B)  This is correct!   The passage explains that in an infected sickle cell, the low-oxygen environment and the low intracellular pH (acidic environment) induce the characteristic sickling in the host cell. This sickling causes the potassium level within the cell to drop, which in turn causes the malaria parasite to die. The passage provides a clear explanation of this process, making option B the correct choice.

(C)  While the passage mentions the low-oxygen environment in the tissue where the sickled cell is sequestered, it does not indicate that the drop in oxygen content is the immediate cause of the malaria parasite's death. The passage focuses on the drop in potassium level as the primary factor leading to the parasite's demise.

(D)  The sequestering of the cell in tissue is a part of the process described in the passage, but it is not the immediate cause of death of the malaria parasite. The passage explains that the parasite develops normally up to the point of sequestering in tissue but dies due to changes within the sickled host cell.

(E)  The passage mentions that the immune system can mount a protective response when the multiplication of the parasite is reduced, but it does not describe the immune system as the immediate cause of death for the malaria parasite within a sickled cell. The primary cause is the drop in potassium level within the host cell.

Answer: B

Sajjad1994 · Answer

Official Explanation

6. The author suggests that in a lethal attack of malaria, which of the following occurs?

Explanation

(A)  This option is not supported by the passage. The passage does discuss the role of intracellular pH in inducing sickling of red blood cells in response to malaria, but it doesn't suggest that the pH drops too slowly. Instead, it emphasizes the low-oxygen environment and low intracellular pH as factors that lead to sickling.

(B)  This is correct!   The passage discusses how malaria is a powerful force with significant effects on human populations, including its high mortality rate. It mentions that malaria kills about 10 percent of its victims directly and contributes to the death of others by decreasing the ability of their immune systems to fight off other infections. Therefore, in a lethal attack of malaria, the rapid spread of the malaria parasites outpaces the host's immune system's ability to respond effectively, ultimately leading to severe illness or death.

(C)  The passage does not provide information to support this option. It focuses on the response of red blood cells to malaria rather than the rate of their production. The discussion revolves around the sickling of existing red blood cells rather than the production of new ones.

(D)  This option is not mentioned in the passage. The passage does discuss the impact of malaria on the host's immune system, but it does not suggest that the introduction of the malaria parasite entirely prevents the immune system from responding.

(E)  This option is not supported by the passage. The passage explains that the sickling of red blood cells occurs in the tissue due to a low-oxygen environment and low intracellular pH, and it does not suggest that there is an insufficient quantity of red blood cells sequestered in tissue for this process to occur.

Answer: B

Sajjad1994 · Answer

Official Explanation

7. Which of the following best describes the organization of the first paragraph?

Explanation

(A)  This is correct!   In the first paragraph, a generalization is presented that lethal genetic diseases should be very rare due to natural selection. However, it then introduces the seemingly surprising fact that certain inherited disorders of red blood cells, such as sickle cell anemia and thalassemia, occur at unusually high frequencies in some populations. The paragraph goes on to explain how this apparent anomaly is reconciled with the generalization through the concept of natural selection favoring genes that provide protection against other lethal diseases, specifically malaria.

(B)  This option does not accurately describe the organization of the first paragraph. The paragraph does not present a thesis that is refuted by a counterexample. Instead, it presents a generalization and reconciles it with a seemingly contradictory observation.

(C)  This option does not accurately describe the organization of the first paragraph. While there is an argument presented about the rarity of lethal genetic diseases and the high frequency of certain red blood cell disorders, the paragraph does not conclude with a general statement derived from the argument. Instead, it provides an explanation for the observed phenomenon.

(D)  This is a reasonably accurate description of the organization of the first paragraph. The paragraph presents an explanation for the high frequency of certain red blood cell disorders and explores it further. However, the primary focus is on reconciling the anomaly rather than examining the explanation in detail.

(E)  This option does not accurately describe the organization of the first paragraph. The paragraph does not present opposing views or clarify differences between views. Instead, it presents a generalization and provides an explanation to address the apparent anomaly.

Answer: A

Sajjad1994 · Answer

Official Explanation

8. Which of the following is most dearly an example of the way in which the majority of fatalities from malaria occur, as the process is described in the passage?

Explanation

(A)  This option is correct because it aligns with the information provided in the passage. The passage mentions that malaria contributes to the death of individuals by decreasing the ability of their immune systems to fight off other infections. In this case, pneumonia is another infection that can be fatal when the immune system is compromised by malaria.

(B)  This option is not supported by the passage. While the passage discusses the impact of malaria on the immune system, it does not specifically mention the victim contracting the flu before dying from malaria. The passage focuses on the general effects of malaria on mortality rates.

(C)  This option is not explicitly supported by the passage. The passage does mention that malaria has a high mortality rate and contributes to early-childhood mortality rates in Africa, but it doesn't specify that death occurs shortly after the first symptoms. The passage provides a more general overview of malaria's impact.

(D)  This option is not supported by the passage. While the passage discusses the high frequency of certain inherited blood disorders in populations exposed to malaria, it does not suggest that individuals quickly die when infected with malaria due to these blood disorders. Instead, it explains that some individuals have developed genetic resistance to malaria.

(E)  This option is not explicitly supported by the passage. The passage mentions that malaria contributes to death by decreasing the ability of the immune system to fight off other infections, but it doesn't specify that death occurs due to repeated bouts of malaria. It focuses on the overall impact of malaria on mortality rates.

Answer: A

meghabaid97 · Answer

Day1 Passage1 :

1.The primary purpose of package is to :
A.   announce that the mechanism of sickle cell anemia has been discovered and to explain why the discovery was so difficult  
 • This choice is partially correct in that the passage does explain the mechanism of how sickle cell blood cells protect against malaria. However, the primary purpose of the passage is not simply to announce the discovery but to explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed.
 • 
B.   explore the limits of natural selection and the way in which certain diseases can transcend them  
 • While the passage does discuss natural selection and the persistence of certain genetic diseases, it is primarily focused on explaining the specific case of how the sickle cell gene persisted due to its advantage against malaria. It does not delve into a broad exploration of the limits of natural selection for all diseases.
C.   describe how sickle cell anemia is produced and where it is most prevalent  
 • While the passage briefly mentions how sickle cell anemia is produced (due to the sickle cell gene) and where it is prevalent (geographical regions with a history of malaria), this is not the primary purpose of the passage. The main focus is on explaining why the gene for sickle cell anemia has persisted.
The primary purpose of the passage is:
D.  explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed. 
The passage discusses the persistence of the gene for sickle cell anemia in populations and how this gene's presence can be explained by its protective advantage against malaria. It also explains how researchers confirmed this explanation by discovering the mechanism of malaria resistance associated with the sickle cell gene.
E.   analyze the effects of malaria on human populations and to suggest a way in which these effects can be minimized  
 • While the passage does discuss the effects of malaria on human populations and the protective role of the sickle cell gene, it does not suggest a way to minimize these effects. Instead, it primarily explains the genetic mechanism behind the protection.
In summary, the primary purpose of the passage is to explain why the gene for sickle cell anemia has persisted and how this explanation was confirmed, making option D the most accurate choice.

Because natural selection acts against genes that cause inherited

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Because natural selection acts against genes that cause inherited

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