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The tsetse fly, belonging to any of [#permalink]
20 Nov 2010, 19:45
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The tsetse fly, belonging to any of approximately twenty species composing the genus Glossina, is indigenous to Africa and is found primarily in forests and savannahs south of the Tropic of Cancer. Dependent on vertebrate blood for nourishment, the tsetse fly is equipped with a long proboscis which is sharp enough to penetrate most animal skins and powerful enough to enable the tsetse to drink quantities of blood up to three times its own body weight.
At the same time that the tsetse drains blood, it can also transmit a variety of dangerous diseases. A bite from a tsetse fly can induce African sleeping sickness in human beings and nagana, a similar ailment, in domestic livestock. The agent of these diseases is the trypanosome, a unicellular, flagellated parasite which feeds primarily on the blood of vertebrates and is generally transmitted by an intermediary leech or insect host, such as the tsetse fly. In humans the trypanosome causes damage to the brain and spinal cord, leading to extreme lethargy and, ultimately, death; in livestock, trypanosomes destroy red blood cells, causing fatal anaemia.
The immune system is ill-equipped to counter trypanosomes. As the immune system attempts to counter disease, antibodies are produced to attack microbes whose antigens, surface proteins, are foreign to the body. However, the trypanosome is capable of disguising itself by altering its genetic code, thereby changing its antigen coating in resistance to each new antibody that evolves. This ―quick change‖ has confounded pathologists and made the development of effective vaccines elusive.
A controversy has been sparked between proponents of the elimination of the tsetse fly and African environmentalists. Those in favour of eradication feel that in addition to reducing disease, the removal of the tsetse fly will open immense tracts of land to cattle breeding. This, however, is precisely what the opposition fears. Environmentalists and conservationists dread the day when cattle and livestock, permitted to roam and graze freely, will uncontrollably devour plush African grasslands, converting them into barren desert. They argue that the tsetse fly must remain for the sake of the land.
With efforts to eradicate the tsetse fly largely unsuccessful, control may offer the only available option for the interests of both health and environment. Since the protozoan cannot be conquered through antibodies or vaccines, scientists have begun efforts to prevent the transmission of the trypanosome parasite by eliminating the tsetse. Attempts to eradicate the tsetse fly, however, have met with little success. Rhodesia used to combat tsetse by extensive brush cleaning, game shooting, and chemical attack, yet the fly persisted. Aerial pesticide treatments have produced inconclusive results.
The reproductive cycle of the tsetse fly is such that a larva pupates underground for several weeks before it emerges as an adult fly. This makes repetitive chemical sweeping at intermittent periods an inconvenient necessity. All of these methods, however, share the weakness of dependence on harmful chemicals, such as DDT, which threaten both the health of the humans who handle them and the environment in which their toxic residues amass.
1. All of the following statements correctly describe the relationship between the tsetse fly, the trypanosome, and vertebrates EXCEPT:
A. vertebrate blood provides the nourishment for the transport of trypanosomes. B. the ―bite‖ of a tsetse fly can kill vertebrates since it often injects a deadly chemical. C. both the tsetse fly and the trypanosome utilize vertebrate blood for nourishment. D. vertebrates may die after trypanosome contamination via a tsetse proboscis. E. the tse tse fly transfers the trypanosome into the vertebrates' bodies
2. In the passage, the author does NOT identify which of the following as a characteristic of the tsetse fly?
A. dependence upon vertebrate blood B. ability to transmit a fatal parasite to livestock and humans C. ability to alter its genetic code D. ability to influence the African cattle population E. its larva pupates for several weeks beneath the ground
3. According to African environmentalists, which of the following accurately describes the effect the tsetse fly has on the African grasslands?
A. If the tsetse fly population continues to exist, the African grasslands will turn into barren wasteland. B. If the tsetse fly population continues to exist, the African grasslands will not be able to provide sufficient food supply for African cattle and livestock. C. Destruction of the tsetse fly population will lead to the conversion of grasslands into desert. D. Destruction of the tsetse fly population will cause overgrowth of the African grasslands. E. Tse tse fly has no impact on grasslands, it only impacts vertebrates
4. What is the primary purpose of the fourth paragraph in the passage
A. to decsribe the harmful effects of the tse tse fly B. to argue that the proliferation of tse tse flies can lead to large scale deforestation of African grasslands C. to discuss a beneficial impact of tse tse flies D. to state that efforts to eradicate the tse tse flies have generally proved to be ineffective E. to discuss the reproductive cycle of a tse tse fly
Last edited by anilnandyala on 20 Nov 2010, 20:00, edited 1 time in total.
answers will be provided after a discussion, proviode ur answers with explanations. 1 q answer c because only tsetse uses blood for nourishment not trpyansome 2 c ability to alter its genetic code is answer because from passage 3 trypansome is capable of changing it's genetic code not insect 3 c Destruction of the tsetse fly population will lead to the conversion of grasslands into desert, an easy one the environmenatalists opposes destroying tsetse because cattle will sweep entire green land in the absence of tsetse 4 c to discuss a beneficial impact of tse tse flies, direct q here the passage offers advantages of tsetse
3/4 in exactly 7:00 min. although i dont agree with answer for the 3rd question . i think it has to be E , because tsotsobe fly has no impact on grasslands, it does not suck the blood out of grass. the fly does not eat the grass either, it only sucks the blood of vertebrates.
and option E exclusively states just that. _________________
What is of supreme importance in war is to attack the enemy's strategy.
option C in q 3 clearly states that elimination of tsotsobe fly WILL lead to conversion of grasslands into deserts . this is a clear exaggeration.
anyone to counter this ?
Question states: "According to African environmentalists".
"C" would be an exaggeration if the Author, not the African environmentalists, were to conclude something based on the premise. Here, the word "will" is used to describe African environmentalists' exact thinking, which is of course an adamant hypothesis, about the effect on grassland upon eradication of tsetse flies.
Environmentalists and conservationists dread the day when cattle and livestock, permitted to roam and graze freely, will uncontrollably devour plush African grasslands, converting them into barren desert. _________________
1. B, D and B somewhat contradict IMO and I liked D better. Passage didn't talk about bite or chemical. 2. C, trypanosome alters code, not the teste fly. 3. C, Less teste's -> more cattle -> less grass -> desert 4. C, Explains the answer in question 3.