The IELTS Reading section tests your ability to understand and interpret text-based information effectively. One common type of passage involves scientific topics, often requiring comprehension of complex relationships and detailed descriptions. Today, we will explore a real IELTS reading passage about the fascinating symbiotic relationship between leaf-cutting ants and the fungus they cultivate. This example will guide you through understanding the passage, answering typical IELTS questions, and avoiding common pitfalls.
The Actual IELTS Reading Passage
Leaf-Cutting Ants and Fungus
A The ants and their agriculture have been extensively studied over the years, but recent research has uncovered intriguing new findings about the fungus they cultivate, how they domesticate it, and how they 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.
B Leaf-cutting ants and their 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.
C 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.
D 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 their gardens free of parasites, don’t you?’ Mr. Currie said of his efforts to find a hidden interloper.
E 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.
F 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 spore-forming stage.
G 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.
H 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.
I 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 the 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.
J 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 leaf-cutters 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.
Leaf-Cutting Ants and Fungus
Reading Questions and Answers
Multiple Matching (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.
A – Leaf-cutting ants
B – Lower attines
C – Both
Build small nests and live with the different foreign fungus.
Answer: BUse toxic leaves to feed the fungus.
Answer: ARaise fungus which doesn’t live with other foreigners.
Answer: AUse substance to fight against Escovopsis.
Answer: CUse dead vegetable to feed the fungus.
Answer: BAre free of parasites explained previously?
Answer: A
Paragraph Matching (Questions 20-24)
Write the correct letter A-J, in boxes 20-24 on your answer sheet.
Dangerous outcome of Escovopsis.
Answer: FThe disadvantage of growing single fungus.
Answer: HComparison of features of two different nests.
Answer: CTwo achievements made by ants earlier than humans.
Answer: JAdvantage of growing a new breed of fungus.
Answer: G
Multiple Choice (Questions 25-26)
Choose the correct letter, A, B, C, or D. Write your answers in boxes 25-26 on your answer sheet.
How does the author think of Currie’s opinion?
A. his viewpoint was verified later.
B. earlier study has sufficient evidence.
C. no details mentioned in the article.
D. his opinion was proved to be wrong.
Answer: AWhat did scientists find on the skin of ants under a microscope?
A. some white cloud mold embedded in their skin.
B. that wax is all over their skin.
C. a substance which is useful to humans.
D. a substance which suppresses the growth of fungus.
Answer: C
Detailed Answers and Explanations
Matching Questions (14-19)
Answer: B
The passage mentions that lower attines build smaller nests and cultivate different fungi compared to leaf-cutters.Answer: A
Leaf-cutters are noted to use fresh vegetation, including toxic leaves, to cultivate their fungus.Answer: A
Leaf-cutters maintain a pure strain of fungus, free from other microorganisms.Answer: C
Both leaf-cutters and lower attines use Streptomyces to combat Escovopsis.Answer: B
Lower attines feed their fungal gardens with detritus like dead leaves.Answer: A
The leaf-cutters strive to keep their fungal gardens free of parasites, as highlighted in the text.
Paragraph Matching (20-24)
Answer: F
Paragraph F discusses the devastating impact of Escovopsis on fungal gardens.Answer: H
Paragraph H explains the inherent risk leaf-cutters face by cultivating a single fungus strain.Answer: C
Paragraph C contrasts the techniques and nesting sizes of leaf-cutters and lower attines.Answer: J
Paragraph J notes that ants discovered antibiotics millions of years before humans and manage monocultural crops sustainably.Answer: G
Paragraph G suggests the evolutionary advantage of lower attines switching fungal strains to outpace Escovopsis.
Multiple Choice (25-26)
Answer: A
The author supports Currie’s hypothesis, mentioning it was later verified despite initial skepticism.Answer: C
Scientists discovered that the white substance on the ants’ cuticle is a living bacterium useful for producing antibiotics.
Common Mistakes in Similar Reading Tasks
- Misinterpreting the Passage: Students often overlook linking phrases that connect ideas.
- Neglecting Context: Without understanding the broader context, distinguishing between similar-sounding statements becomes difficult.
- Matching Errors: Be attentive to the specific wording in both the questions and the passage to avoid incorrect matches.
Challenging Vocabulary
- Symbiosis (noun) /ˌsɪm.baɪˈəʊ.sɪs/: A mutually beneficial relationship between different organisms.
- Pathogen (noun) /ˈpæθ.ə.dʒən/: An organism that causes disease.
- Detritus (noun) /dɪˈtraɪ.təs/: Dead plant or animal matter.
Difficult Grammar Structures
Complex Sentences with Relative Clauses
Structure: Main clause + that/which/who + relative clause.
Example: “The leaf-cutters’ fungus, which has been cultivated by the ants for millions of years, is prone to infection.”
By mastering passage comprehension and tackling complex scientific subjects, you can significantly boost your performance in the IELTS Reading section. This intricate look at the leaf-cutting ants and their fungus highlights the importance of detail-oriented reading and contextual understanding. Good luck with your studies!