RC Practice - 13th July
Since some of the dead animals never washed ashore, the overall disaster was presumably worse; perhaps 50 percent of the population died. A dolphin die-off of this character and magnitude had never before been observed; furthermore, the dolphins exhibited a startling range of symptoms. The research team that examined the die-off noted the presence of both skin lesions and internal lesions in the liver, lung, pancreas and heart, which suggested a massive opportunistic bacterial infection of already weakened animals. Tissues from the stricken dolphins were analyzed for a variety of toxins. Brevetoxin, a toxin produced by the blooming of the alga Ptychodiscus brevis, was present in eight out of seventeen dolphins tested. Tests for synthetic pollutants revealed that polychlorinated biphenyls (PCBs) were present in almost all animals tested. The research team concluded that brevetoxin poisoning was the most likely cause of the illnesses that killed the dolphins. Although P. brevis is ordinarily not found along the Atlantic coast, an unusual bloom of this organism—such blooms are called “red tides” because of the reddish color imparted by the blooming algae—did occur in the middle of the affected coastline in October 1987. These researchers believe the toxin accumulated in the tissue of fish and then was ingested by dolphins that preyed on them. The emaciated appearance of many dolphins indicated that they were metabolizing their blubber reserves, thereby reducing their buoyancy and insulation (and adding to overall stress) as well as releasing stores of previously accumulated synthetic pollutants, such as PCBs, which further exacerbated their condition. The combined impact made the dolphins vulnerable to opportunistic bacterial infection, the ultimate cause of death. For several reasons, however, this explanation is not entirely plausible. First, bottlenose dolphins and P. brevis red tides are both common in the Gulf of Mexico, yet no dolphin die?off of a similar magnitude has been noted there. Second, dolphins began dying in June, hundreds of miles north of and some months earlier than the October red tide bloom. Finally, the specific effects of brevetoxin on dolphins are unknown, whereas PCB poisoning is known to impair functioning of the immune system and liver and to cause skin lesions; all of these problems are observed in the diseased animals. An alternative hypothesis, which accounts for these facts, is that a sudden influx of pollutants, perhaps from offshore dumping, triggered a cascade of disorders in animals whose systems were already heavily laden with pollutants. Although brevetoxin may have been a contributing factor, the event that actually precipitated the die-off was a sharp increase in the dolphins’ exposure to synthetic pollutants.
1. According to the author, which of the following correctly describes the chain of events that led to the death of dolphins?
(A) The abnormal growth of alga P. brevis resulted in toxin accumulation in fish, dolphins fed on this fish, their immunity got compromised, a surge in pollutant PCB worsened their system and bacterial infection became the final nail in their coffin. (B) An unusual surge in pollutant PCB stressed dolphins’ immune responses and led to high levels of toxins, the growth of alga P.brevis exacerbated the immune system and more PCB dumped offshore led to organ failure and death
(C) Bacterial infection compromised dolphins’ immunity, offshore dumping of PCB pollutant led to poisoning, and the toxin accumulation due to excessive growth of P.brevis led to organ failure and death
(D) An unusual surge in PCB pollutants triggered stressful immune responses, the excessive growth of P.brevis led to accumulation of toxins, further worsening their condition, and this compromised immune system probably gave up to a bacterial infection
2. The passage is primarily concerned with
(A) assessing the effects of a devastating bacterial infection in Atlantic coast bottlenose dolphins
(B) pointing out the weaknesses in the research methodology used to explore the dolphin die-off
(C) discussing relative effects of various marine pollutants in dolphin die-off in Atlantic coast
(D) advancing possible alternative explanations for the massive dolphin die-off
3. Which one of the following is most analogous to the approach taken by author of the passage with regard to the research described in the third paragraph?
(A) A physics teacher accepts the data from a student’s experiment but questions the student’s conclusions.
(B) An astronomer provides additional observations to support another astronomer’s theory.
(C) A cook revises a traditional recipe by substituting modern ingredients for those used in the original.
(D) A doctor prescribes medication for a patient whose illness was misdiagnosed by another doctor.
4. It can be inferred from the passage that the author would most probably agree with which one of the following statements about brevetoxin?
(A) It may have been responsible for the dolphins’ skin lesions but could not have contributed to the bacterial infection.
(B) It forms more easily when both P. brevis and synthetic pollutants are present in the environment simultaneously.
(C) It damages liver function and immune system responses in bottlenose dolphins but may not have triggered this particular dolphin die-off.
(D) It is unlikely to have caused the die-off because it was not present in the dolphins’ environment when the die-off began.
5. The explanation for the dolphin die-off given by the research team most strongly supports which one of the following?
(A) When a dolphin metabolizes its blubber, the PCBs released may be more dangerous to the dolphin than they were when stored in the blubber.
(B) When P. brevis blooms in an area where it does not usually exist, it is more toxic than it is in its usual habitat.
(C) Opportunistic bacterial infection is usually associated with brevetoxin poisoning in bottlenose dolphins.
(D) The dolphins’ emaciated state was probably a symptom of PCB poisoning rather than of brevetoxin poisoning.
6. It can be inferred from the passage that opportunistic infection refers to
(A) infections induced by humans for their greedy purposes
(B) infections caused by microbes which usually do not
(C) infections accompanied with toxins
(D) infections causing compromised immunity
Answers of today's RC :- https://youtu.be/X1VYNpre7EE