IELTS Academic Reading Practice Test 427

Visitors to the rainforest of the Ituri region, in the north-east of the Democratic Republic of the Congo, may be shown an animal that seems assembled from parts of several others. It has the body of a small horse, the neck and ears of a giraffe, and the striped legs of a zebra. This is the okapi, a shy forest mammal that remained unknown to scientists until the beginning of the twentieth century, although people living in the forest had hunted it for generations. Its existence became known only when a British official obtained skins and skulls and sent them to Europe.

The official was Harry Johnston, then serving as a colonial administrator in Uganda, who heard reports of an unusual animal in the forests to the west and asked local hunters to obtain specimens. A complete skin, with skulls, eventually reached London, where zoologists examined it in 1901. Because of the stripes, the first descriptions treated the creature as a kind of forest horse. Closer study showed that it was related to the giraffe, and it was given the scientific name Okapia johnstoni, the second word honouring Johnston. The name okapi itself comes from a word used by people of the region.

An adult okapi stands about 1.5 metres high at the shoulder and weighs between 200 and 300 kilograms, and females are on average larger than males. The coat is dense, slightly oily and velvety to the touch, and it sheds rain effectively in a forest where damp is constant. White stripes run across the hindquarters and continue down the upper part of the legs, becoming narrower as they descend. Only males carry short, skin-covered horns, known as ossicones; females have small bony bumps instead, topped with a tuft of hair.

Its most striking feature, however, is the tongue. Long, flexible and bluish-grey, it can grasp foliage, strip leaves from twigs and even clean the animal's own ears and eyes. Okapis are browsers rather than grazers, feeding on the leaves, buds and young shoots of many plant species. They also visit salt licks to obtain minerals that are scarce in their usual diet. Like the giraffe, the okapi is a ruminant: its four-chambered stomach contains micro-organisms that break down tough plant material.

Okapis are secretive and largely solitary. Adults occupy overlapping home ranges, and meetings between them are usually brief. They appear to keep in touch at a distance with soft coughing calls, and their large ears, which can turn independently, pick up faint sounds that may reveal a leopard, their main predator, or a human hunter. The animals are active mainly by day, but they are hard to observe in the gloom of the understory, so much of what is known about their habits comes from tracks, droppings and automatic cameras rather than from watching them.

A female gives birth after a pregnancy of about fourteen and a half months, usually to a single calf. For the first weeks the calf lies hidden in dense vegetation, staying motionless while its mother feeds nearby and returning to her to nurse. Its striped coat helps it to disappear among the shadows and shafts of light on the forest floor. The young animal begins to eat solid food within a few months and becomes independent at around a year old. In captivity, okapis have lived for well over twenty years.

The purpose of the stripes has been much discussed. Because the forest is a place of broken light and deep shade, contrasting bands may help to break up the outline of an animal seen through leaves, a principle known as disruptive coloration. Zoologists have also suggested that the pattern allows a calf to recognise and follow its mother in dim light. None of these explanations has been tested experimentally, and more than one may be partly correct.

Whatever purpose the stripes serve, the okapi's future is uncertain. The species is classified as Endangered. Its range is confined to forests in the north-east of the country, a region that has suffered decades of logging, clearance for farmland, mining for minerals such as coltan and gold, and armed conflict. Okapis are hunted for meat and caught in snares set for other animals. In 1992 the government created the Okapi Wildlife Reserve, covering some 13,000 square kilometres of forest; four years later it was added to the list of World Heritage Sites, and its headquarters at Epulu has kept okapis for research and breeding for decades.

The reserve has not been safe. In 2012 armed men attacked its headquarters, killing staff and a number of the okapis kept there. The size of the wild population is unknown. Okapis are so elusive that conventional counting methods are of little use, and published estimates vary widely. Camera-trap surveys have confirmed that the animals survive in parts of the forest where they had not been recorded for years, but such surveys cover only small areas.

For communities of the Ituri forest the okapi has long been a familiar neighbour rather than a scientific curiosity, and its image appears on the country's postage stamps and banknotes. For zoologists it remains a reminder of how much can survive unrecorded: an animal the size of a pony, living in forests crossed by traders and officials, escaped the notice of science until 1901. Whether it survives the present century may depend less on the rainforest itself than on the people who govern and live in the region.

Ice floats. This simple observation is unusual: for most substances the solid form is denser than the liquid, so a lump of solid sinks in its own melt. Water does the opposite. It reaches its greatest density not at its freezing point but at about 4 °C, and both warming and cooling from that temperature make it expand. The result is that a pond in winter acquires a lid of ice while remaining liquid beneath, and that fish and insects continue to live in water that would otherwise have frozen solid.

The explanation lies in the way water molecules attract one another. Each molecule has a slight electrical imbalance, with a negative end and a positive end, so neighbouring molecules are drawn together by what chemists call hydrogen bonds. In liquid water these bonds are constantly made and broken, and as the liquid cools the molecules move more slowly and can pack more closely, which is why water contracts as it approaches 4 °C. Below that temperature something else begins to happen. The molecules start to arrange themselves into the open, six-sided pattern of ice, in which each molecule is bonded to four others, leaving relatively large gaps in the structure.

A lake behaves like a very large, very slow experiment in density. In autumn, as the air cools, the surface water loses heat and contracts. Once it is denser than the water below it, it sinks, and warmer water rises to take its place. This process continues, and because the lake is also stirred by wind, the upper layers are soon mixed. The whole body of water gradually approaches 4 °C, carrying oxygen down to the bottom and bringing up nutrients that had settled there. Limnologists, the scientists who study inland waters, call this autumn mixing the turnover.

The behaviour changes once the lake as a whole is close to that temperature. Cooling now makes the surface water slightly less dense rather than more, so it stays where it is, on top. It can therefore continue to lose heat while the water beneath it remains close to 4 °C, and it may reach 0 °C within a few days. Even then it does not always freeze at once. Freezing requires the formation of a crystal, and in still, clean water the first crystal may be slow to appear; the water can be supercooled a degree or two below zero before ice begins to spread across the surface.

Once a sheet of ice has formed, it insulates the water underneath. Ice is a poor conductor of heat, and the layer of still water immediately below it is poorer still. Heat from the deeper water must therefore pass slowly through the ice, and the rate at which the ice thickens is limited by this. In a deep lake in a temperate climate, the ice may be no more than half a metre thick at the end of winter, and the water a few metres down remains liquid all year.

The consequences for living things are considerable. Because the ice floats, the water beneath it stays liquid, at least in lakes deep enough to store summer heat, and fish, insect larvae and amphibians survive the winter there. If ice were denser than water, the crystals would sink as they formed and the lake would freeze from the bottom upwards, with no insulating lid at the surface. In cold regions, shallow lakes might then freeze solid, and much freshwater life would be unable to persist.

The same physics produces the layering that is visible in summer, when the sun warms the surface faster than wind can mix it. Warm, light water then floats on cold, dense water, and between the two lies a zone where the temperature falls sharply with depth. This boundary, the thermocline, acts as a barrier that prevents the upper and lower layers from mixing, so that the deep water can slowly lose its oxygen while the surface becomes warm and bright. Only when autumn cooling erases the difference in density does the lake turn over again.

Lakes that mix twice a year in this way are described as dimictic, and they are characteristic of the temperate zone. Elsewhere the pattern differs. Some deep lakes in milder climates mix only once, in winter. Tropical lakes may never reach a uniform temperature and so never turn over completely, while shallow lakes are mixed so easily by wind that their behaviour is governed less by density than by their exposure. Saline lakes freeze at temperatures below zero, and the saltier the water, the lower the temperature at which ice appears.

Much remains uncertain. The details of how the first ice crystal forms in a natural lake are still debated; dust, bubbles and even certain bacteria can serve as nuclei. Records of the dates on which lakes freeze and thaw are among the longest indirect measures of climate available: observations at Lake Suwa in Japan go back to the fifteenth century, and a network of similar records has been used to show that freezing now generally happens later than it did a century ago. How much of that shift is caused by rising air temperature, and how much by changes in wind and cloud, is still being worked out.

Few questions in education provoke as much disagreement as how to judge what a student has learned. The written examination, taken under supervision and marked anonymously, has dominated secondary schooling for more than a century. Coursework — essays, projects and practical investigations completed over weeks or months and assessed by the student's own teachers — became common in the second half of the twentieth century, and in many countries the two now sit side by side. England's reforms to A-levels from 2015 cut coursework from most subjects, while the International Baccalaureate retains teacher-marked internal assessment in every subject it offers. The question, then, is not whether one method exists but whether the balance should shift further towards coursework.

Teachers who defend coursework begin with what it can measure. A timed paper rewards speed and recall; a project can require a student to plan, revise and respond to sources over several weeks, which is closer to the work of a historian or an engineer. Teachers also value the feedback loop: drafting a piece and improving it teaches more than a single grade at the end of a course. In subjects with a practical dimension, from art to design technology, a portfolio is the only credible record of what a student can do. A single project may run for half a term and draw on several sources, which is why its defenders see it as a better preparation for university study, where such work is the norm. None of this, defenders concede, makes coursework easy to assess fairly.

The objections are equally serious. Work completed at home cannot be authenticated with confidence. Parents, tutors and, increasingly, artificial-intelligence tools can all contribute, and a teacher cannot always tell whose words are on the page. Examination boards point out that marking by different teachers in different schools is not naturally comparable: one department's generous grade is another's strict one, and moderation by sample corrects only some of the variation. Coursework also places a heavy load on teachers, who must design tasks, supervise them and mark them, often without extra time. The result, critics say, is a qualification that is harder to defend than an examination.

Examination boards have an institutional interest in exams, and their critics say so. Yet the case they make is not merely commercial. A written paper sat under identical conditions allows two candidates in different towns to be compared on the same tasks, and the script can be re-marked if a result is challenged. Security is easier to maintain: papers are kept sealed until the day, and malpractice can be investigated with a clear trail. Boards also argue that exams are cheaper per candidate than the supervision and moderation that extended work demands, although the difference is rarely quantified in public.

Universities are often assumed to favour examinations because they use them. In practice, undergraduate assessment is mixed: essays, laboratory reports and dissertations are marked throughout the year, and many departments now weight final exams less heavily than they did a generation ago. What admissions tutors say they want is a reliable signal of a candidate's ability, and here the evidence is mixed. Examination results predict first-year performance reasonably well in some subjects; in others, a portfolio or an extended essay reveals qualities that a three-hour paper cannot. Professional courses in medicine and law still require timed examinations because competence must be demonstrated under controlled conditions.

Students themselves are divided, and their reasons are practical. Those who favour coursework describe the freedom to work at their own pace, to read widely and to recover from a bad week. Those who prefer exams describe the relief of a deadline that is fixed and a revision period that ends. Anxiety about examinations is well documented, but so is anxiety about overlapping coursework deadlines in the final year.

Parents tend to speak about fairness rather than pedagogy. A family that can afford a private tutor, or a parent with a degree in the subject, can support a long project in ways that are invisible to the school. Parents also worry about the pressure of a single examination season, and many say they would welcome assessment spread across the year. Yet the same parents often distrust coursework when their own child's grade depends on a neighbour's classroom, and they ask a reasonable question: how does a school show that the work is the student's own?

My own view is that neither format deserves to replace the other. Coursework is better at developing and revealing the skills of research, drafting and sustained argument; examinations are better at guaranteeing authenticity and comparability. A sensible system therefore keeps both and adjusts their weight by subject: more project work in the humanities and in practical subjects, more timed assessment where secure knowledge matters and where the risk of outside help is greatest. Where coursework is used, three safeguards should be non-negotiable: some drafting in class under supervision, external moderation of a sample, and a short oral defence for a substantial project.

The real question, then, is not 'coursework or exams' but what each is asked to certify. Exams certify that a candidate can perform unaided on a given day; coursework certifies what a candidate can produce with time, resources and feedback. Both are legitimate purposes, and a qualification that reports only one of them tells universities, employers and students a partial truth. The argument for replacing written examinations entirely is, on the available evidence, weaker than the argument for rebalancing them carefully.