Giải đề thi thật IELTS Reading – Leaf-cutting Ants and Fungus

Giải đề thi thật IELTS Reading – Leaf-cutting Ants and Fungus

1. The ants and then agriculture have been extensively studied over the years, but the recent research has uncovered intriguing new findings about the fungus they cultivate, how they domesticated it and how they cultivate it and preserve it from pathogens. For example, the fungus farms, which the ants were thought to keep free of pathogens, turn out to be vulnerable to a devastating mold, found nowhere else but in ants’ nests. To keep the mold in check, the ants long ago made a discovery that would do credit to any pharmaceutical laboratory
2. Leaf-cutting ants and then fungus farms are a marvel of nature and perhaps the best known example of symbiosis, the mutual dependence of two species. The ants’ achievement is remarkable — the biologist Edward O. Wilson has called it “one of the major breakthroughs in animal evolution” — because it allows them to eat, courtesy of their mushroom’s digestive powers, the otherwise poisoned harvest of tropical forests whose leaves are laden with terpenoids, alkaloids and other chemicals designed to sicken browsers.
3. Fungus growing seems to have originated only once in evolution, because all gardening ants belong to a single tribe, the descendants of the first fungus farmer. There are more than 200 known species of the attine ant tribe, divided into 12 groups, or genera. The leaf-cutters use fresh vegetation; the other groups, known as the lower attines because their nests are smaller and their techniques more primitive, feed their gardens with detritus like dead leaves, insects and feces.
4. The leaf-cutters’ fungus was indeed descended from a single strain, propagated clonally, or just by budding, for at least 23 million years. But the lower attine ants used different varieties of the fungus, and in one case a quite separate species, the four biologists discovered. The pure strain of fungus grown by the leaf-cutters, it seemed to Mr. Currie, resembled the monocultures of various human crops, that are very productive for a while and then succumb to some disastrous pathogen, such as the Irish potato blight.

Monocultures, which lack the genetic diversity to respond to changing environmental threats, are sitting ducks for parasites. Mr. Currie felt there had to be a parasite in the ant fungus system. But a century of ant research offered no support for the idea. Textbooks describe how leaf-cutter ants scrupulously weed their gardens of all foreign organisms. “People kept telling me, ‘You know the ants keep then gardens free of parasites, don’t you?’” Mr. Currie said of his efforts to find a hidden interloper.

1. But after three years of sifting through attine ant gardens, Mr. Currie discovered they are far from free of infections. In last month’s issue of the Proceedings of the National Academy of Sciences, he and two colleagues, Dr. Mueller and David Mairoch, isolated several alien organisms, particularly a family of parasitic molds called Escovopsis.
2. Escovopsis turns out to be a highly virulent pathogen that can devastate a fungus garden in a couple of days. It blooms like a white cloud, with the garden dimly visible underneath. In a day or two the whole garden is enveloped. “Other ants won’t go near it and the ants associated with the garden just starve to death,” Dr. Rehner said. “They just seem to give up, except for those that have rescued their larvae.” The deadly mold then turns greenish-brown as it enters its sporeforming stage.
3. Evidently the ants usually manage to keep Escovopsis and other parasites under control. But with any lapse in control, or if the ants are removed, Escovopsis will quickly burst forth. Although new leaf-cutter gardens start off free of Escovopsis, within two years some 60 percent become infected. The discovery of Escovopsis’s role brings a new level of understanding to the evolution of the attine ants.

“In the last decade, evolutionary biologists have been increasingly aware of the role of parasites as driving forces in evolution,” Dr. Schultz said. There is now a possible reason to explain why the lower attine species keep changing the variety of fungus in their mushroom gardens, and occasionally domesticating new ones — to stay one step ahead of the relentless Escovopsis.

1. Interestingly, Mr. Currie found that the leaf-cutters had in general fewer alien molds in their gardens than the lower attines, yet they had more Escovopsis infections. It seems that the price they pay for cultivating a pure variety of fungus is a higher risk from Escovopsis. But the leaf-cutters may have little alternative: they cultivate a special variety of fungus which, unlike those grown by the lower attines, produces nutritious swollen tips for the ants to eat.
2. Discovery of a third partner in the ant-fungus symbiosis raises the question of how the attine ants, especially the leaf cutters, keep this dangerous interloper under control. Amazingly enough, Mr. Currie has again provided the answer. “People have known for a hundred years that ants have a whitish growth on the cuticle,” said Dr. Mueller, referring to the insects’ body surface. “People would say this is like a cuticular wax. But Cameron was the first one in a hundred years to put these things under a microscope. He saw it was not inert wax. It is alive.”

Mr. Currie discovered a specialized patch on the ants’ cuticle that harbors a particular kind of bacterium, one well known to the pharmaceutical industry, because it is the source of half the antibiotics used in medicine. From each of 22 species of attine ant studied, Mr. Cameron and colleagues isolated a species of Streptomyces bacterium, they reported in Nature in April.

The Streptomyces does not have much effect on ordinary laboratory funguses. But it is a potent poisoner of Escovopsis, inhibiting its growth and suppressing spore formation. It also stimulates growth of the ants’ mushroom fungus. The bacterium is carried by virgin queens when they leave to establish new nests, but is not found on male ants, playboys who take no responsibility in nest-making or gardening.

1. Because both the leaf-cutters and the lower attines use Streptomyces, the bacterium may have been part of their symbiosis for almost as long as the Escovopsis mold. If so, some Alexander Fleming of an ant discovered antibiotics millions of years before people did. Even now, the ants are accomplishing two feats beyond the powers of human technology. The leafcutters are growing a monocultural crop year after year without disaster, and they are using an antibiotic apparently so wisely and prudently that, unlike people, they are not provoking antibiotic resistance in the target pathogen.

Questions

Questions 14–19

Use the information in the passage to match the options (listed A–C) with activities or features of ants below.
Write the appropriate letters A–C in boxes 14–19 on your answer sheet.
NB: you may use any letter more than once

14 Build small nests and live with different foreign fungus.
15 Use toxic leaves to feed fungus.
16 Raise fungus which don’t live with other variety of foreigners.
17 Use substance to fight against escovopsis.
18 Use dead vegetable to feed fungus.
19 Normally keep a highly dangerous parasite under control.

Questions 20–24

The reading Passage has ten paragraphs A–J. Which paragraph contains the following information? Write the correct letter A–J, in boxes 20–24 on your answer sheet.

20 The dangerous outcome of Escovopsis.
21 The disadvantage of growing a single fungus.
22 Comparison of features of two different nests.
23 Two achievements were made by ants earlier than humans.
24 The advantage of growing a new breed of fungus.

Questions 25–26

Choose the correct letter, A, B, C or D.
Write your answers in boxes 25–26 on your answer sheet.

25 How does author think of Currie’s opinion?
A. his viewpoint was verified later.
B. earlier study has sufficient evidence,
C. no details mentioned in article.
D his opinion was proved to be wrong.

26 What did scientists find on the skin of ants under microscope?
A. some white cloud mold embed in their skin
B. that Wax is all over their skin,
C. a substance which is useful to humans.
D. a substance which suppresses growth of fungus.

Giải chi tiết Questions 14-19 (Matching features)

Q14. Build small nests and live with the different foreign fungus.
Đáp án: B Lower attines

• Đoạn C: “the other groups, known as the lower attines because their nests are smaller… feed their gardens with… detritus…
• Đoạn D: “the lower attine ants used different varieties of the fungus, and in one case a quite separate species.”
  → “Small nests” + “different fungus” = lower attines.

Q15.  Use toxic leaves to feed fungus.
Đáp án: A Leaf-cutting ants

• Đoạn B: nói về leaf-cutting ants và nấm giúp chúng ăn được “leaves… laden with terpenoids, alkaloids and other chemicals designed to sicken browsers.”
  → Chỉ leaf-cutting ants dùng lá (tươi, có chất độc) cho nấm.

Q16.  Raise fungus which don’t live with other variety of foreigners.

Đáp án: A Leaf-cutting ants

• Đoạn D: “The leaf-cutters’ fungus… descended from a single strain…”
• Đoạn H: “leaf-cutters had in general fewer alien molds in their gardens than the lower attines” → vườn nấm khá “thuần”, ít “foreigners”.
  → Nấm của leaf-cutting ants là giống thuần, ít nấm lạ sống chung.

Q17.  Use substance to fight against escovopsis.

Đáp án: C Both

• Đoạn I–J: trên da kiến có Streptomyces – vi khuẩn “well known… source of half the antibiotics used in medicine” và “a potent poisoner of Escovopsis”.
• Đoạn J: “Because both the leaf-cutters and the lower attines use Streptomyces…”
  → Cả A và B đều dùng chất (vi khuẩn) để chống Escovopsis → C.

Q18.  Use dead vegetables to feed the fungus.

Đáp án: B (Lower attines)

• Đoạn C: “the lower attines… feed their gardens with detritus like dead leaves, insects and feces.”
  → Chỉ lower attines dùng lá chết / mảnh vụn.

Q19. Normally keep a highly dangerous parasite under control. 

Đáp án: A Leaf-cutting ants

• Đoạn F mô tả Escovopsis cực kỳ nguy hiểm.
• Đoạn G: “Evidently the ants usually manage to keep Escovopsis and other parasites under control.” – “the ants” ở đây là cả bộ tộc attine, gồm leaf-cutters và lower attines.
  → Bình thường cả hai nhóm đều kiểm soát được ký sinh này → C.

Giải chi tiết Questions 20-24 (Matching Information Paragraph)

Q20. The dangerous outcome of Escovopsis.

 Đáp án: F

• Đoạn F: mô tả chi tiết hậu quả:
  • “can devastate a fungus garden in a couple of days”
  • “Other ants won’t go near it… the ants… just starve to death”
    → Đây là đoạn nói kết cục nguy hiểm khi Escovopsis bùng phát.

Q21. The disadvantage of growing a single fungus.

 Đáp án: D

• Đoạn D: nấm của leaf-cutters là một dòng thuần (single strain / monoculture) và “Monocultures… are sitting ducks for parasites.”
  → Nhược điểm: thiếu đa dạng di truyền → rất dễ bị ký sinh / dịch bệnh.

Q22. Comparison of features of two different nests.

 Đáp án: C

• Đoạn C so sánh leaf-cutters và lower attines:
  • Leaf-cutters: dùng fresh vegetation.
  • Lower attines: “nests are smaller”, kỹ thuật “primitive”, dùng dead leaves, insects, feces.
    → Đây là đoạn so sánh đặc điểm hai loại tổ / hệ thống làm nông.

Q23. Two achievements were made by ants earlier than humans.

 Đáp án: J

• Đoạn J:
  • “some Alexander Fleming of an ant discovered antibiotics millions of years before people did.” → phát hiện “kháng sinh” trước con người.
  • “Even now, the ants are accomplishing two feats beyond the powers of human technology…”
    • trồng monoculture mà không bị sụp đổ
    • dùng antibiotic mà không làm xuất hiện kháng thuốc.
      → Hai “thành tựu” (liên quan kháng sinh & kiểm soát monoculture) gắn với kiến, trước và vượt con người.

Q24. The advantage of growing a new breed of fungus.

 Đáp án: G

• Đoạn G: giải thích vì sao lower attines “keep changing the variety of fungus… and occasionally domesticating new ones — to stay one step ahead of the relentless Escovopsis.”
  → Lợi ích của việc “nuôi giống nấm mới”: giúp kiến luôn đi trước ký sinh Escovopsis một bước.

Giải chi tiết Questions 25-26 (Multiple choice)

25. How does author think of Currie’s opinion?

 Đáp án: A. his viewpoint was verified later.

• Currie nghi ngờ hệ nấm-kiến kiểu monoculture phải có ký sinh (đoạn D), dù “a century of ant research offered no support” và sách nói vườn nấm sạch ký sinh.
• Sau 3 năm (đoạn E), ông tìm ra Escovopsis → ý kiến của ông được chứng minh đúng.

→ Nên chọn A, không phải D.

26. What did scientists find on the skin of ants under microscope?

 Đáp án: C. a substance which is useful to humans.

• Đoạn I: lớp trắng trên cuticle không phải sáp mà là vi khuẩn Streptomyces – “well known to the pharmaceutical industry… source of half the antibiotics used in medicine.”
  → Đây là chất (vi khuẩn) rất hữu ích với con người.
• Nó cũng “poisons Escovopsis”, nhưng bài nhấn mạnh trước hết là nguồn kháng sinh y học → khớp với câu C hơn D

Tổng hợp giải đề IELTS Writing và Speaking biên soạn bởi đội ngũ chuyên môn nhà Cú.

LIST TỪ VỰNG TỪ BÀI IELTS READING

• symbiosis /ˌsɪmbiˈəʊsɪs/ – mối cộng sinh (hai loài sống phụ thuộc lẫn nhau)
• mutual dependence /ˌmjuːtʃuəl dɪˈpendəns/ – sự phụ thuộc lẫn nhau
• breakthrough /ˈbreɪkθruː/ – bước đột phá lớn
• evolution /ˌiːvəˈluːʃn/ – sự tiến hóa
• tribe /traɪb/ – bộ (nhóm phân loại trong sinh học)
• genus (pl. genera) /ˈdʒiːnəs/ – chi (trong phân loại sinh học)
• monoculture /ˈmɒnəkʌltʃə(r)/ – độc canh, chỉ trồng/nuôi một giống duy nhất
• strain (of fungus) /streɪn/ – chủng (nấm, vi khuẩn…)
• propagate clonally /ˈprɒpəɡeɪt ˈkləʊnəli/ – nhân giống vô tính, nhân lên từ một dòng duy nhất
• pathogen /ˈpæθədʒən/ – mầm bệnh, tác nhân gây bệnh
• parasite /ˈpærəsaɪt/ – ký sinh trùng
• parasitic mold /ˌpærəˈsɪtɪk məʊld/ – nấm mốc ký sinh
• virulent /ˈvɪrjʊlənt/ – cực độc, có độc lực mạnh (dễ gây hại nghiêm trọng)
• devastate /ˈdevəsteɪt/ – tàn phá, hủy diệt
• envelop /ɪnˈveləp/ – bao trùm, bao phủ hoàn toàn
• infection /ɪnˈfekʃn/ – sự nhiễm bệnh, sự nhiễm trùng
• spore /spɔː(r)/ – bào tử (đơn vị sinh sản của nấm, vi khuẩn…)
• spore-forming stage /spɔː ˌfɔːˈmeɪʃn steɪdʒ/ – giai đoạn hình thành bào tử
• alien organism /ˈeɪliən ˈɔːɡənɪzəm/ – sinh vật lạ, sinh vật ngoại lai
• sitting duck (for parasites) /ˌsɪtɪŋ ˈdʌk/ – mục tiêu dễ bị tấn công, “mồi ngon” cho ký sinh
• vulnerable (to sth) /ˈvʌlnərəbl/ – dễ bị tổn thương, dễ bị tấn công
• terpenoids /ˈtɜːpɪnɔɪdz/ – hợp chất tecpenoit (hóa chất trong lá cây, thường có mùi, có thể độc)
• alkaloids /ˈælkəlɔɪdz/ – ancaloit (hợp chất có nitơ, thường có độc tính như trong lá, hạt cây)
• laden with /ˈleɪdn wɪð/ – chứa đầy, nặng trĩu (vì có nhiều cái gì đó)
• detritus /dɪˈtraɪtəs/ – mảnh vụn hữu cơ (lá khô, xác côn trùng…)
• feces (BrE: faeces) /ˈfiːsiːz/ – phân, chất thải (của động vật)
• cuticle /ˈkjuːtɪkl/ – lớp vỏ ngoài (trên da côn trùng), lớp biểu bì
• specialized patch /ˈspeʃəlaɪzd pætʃ/ – mảng chuyên biệt, vùng chuyên hóa
• pharmaceutical industry /ˌfɑːməˈsuːtɪkl ˈɪndəstri/ – ngành dược phẩm
• antibiotic /ˌæntibaɪˈɒtɪk/ – thuốc kháng sinh
• inhibit (growth) /ɪnˈhɪbɪt/ – ức chế (sự phát triển)
• suppress (spore formation) /səˈpres/ – kìm hãm, ngăn chặn (quá trình hình thành bào tử)
• nutritious /njuˈtrɪʃəs/ – giàu dinh dưỡng
• swollen tips /ˈswəʊlən tɪps/ – phần chóp/phần đầu bị phồng to (ví dụ: đầu nấm phình ra làm thức ăn)