The Evolutionary Mystery: Crocodile Survives - IELTS Reading Answers & Explanations
From IELTS Recent Actual Test 6 Academic Reading Test 3 · Part 2 · Questions 15–27
Reading Passage
You should spend about 20 minutes on Questions 15-27, which are based on Reading Passage 2 below.
The Evolutionary Mystery: Crocodile Survives
A Even though crocodiles have existed for 200 million years, they're anything but primitive. As crocodiles' ancestors, crocodilia came to adapt to an aquatic lifestyle. When most of the other contemporary reptiles went extinct, crocodiles were able to make it because their bodies changed and they adapted better to the climate. They witnessed the rise and fall of the dinosaurs, which once ruled the planet, and even the 65 million years of alleged mammalian dominance didn't wipe them off. Nowadays, the crocodiles and alligators are not that different from their prehistoric ancestors, which proves that they were (and still are) incredibly adaptive.
B The first crocodile-like ancestors came into existence approximately 230 million years ago, and they had many of the features which make crocodiles natural and perfect stealth hunters: streamlined body, long tail, protective armour and long jaws. They are born with four short, webbed legs, but this does not mean that their capacity to move on the ground shall ever be underestimated. When they move, they are so fast that you won't even have any chance to try making the same mistake again by getting too close, especially when they're hunting.
C Like other reptiles, crocodiles are poikilothermal animals (commonly known as cold-blooded, whose body temperature changes with that of the surroundings) and consequently, require exposure to sunlight regularly to raise body temperature. When it is too hot, they would rather stay in water or shade. Compared with mammals and birds, crocodiles have a slower metabolism, which makes them less vulnerable to food shortage. In the most extreme case, a crocodile can slow its metabolism down even further, to the point that it would survive without food for a whole year, enabling them to outlive mammals in relatively volatile environments.
D Crocodiles have a highly efficient way to prey catching. The prey rarely realises there might be a crocodile under the water because the crocodile makes a move without any noise or great vibration when spotting its prey. It only keeps its eyes above the water level. As soon as it feels close enough to the victim, it jerks out of the water with its wide open jaws. Crocodiles are successful because they are capable of switching feeding methods. It chases after fish and snatches birds at the water surface, hides in the waterside bushes in anticipation of a gazelle, and when the chance to ambush presents itself, the crocodile dashes forward, knocks the animal out with its powerful tail and then drags the prey into the water to drown.
E In many crocodilian habitats, the hot season brings drought that dries up their hunting grounds, leaving it harder for them to regulate body temperatures. This actually allowed reptiles to rule. For instance, many crocodiles can protect themselves by digging holes and covering themselves in mud, waiting for months without consuming any food or water until the rains finally return. They transform into a quiescent state called aestivation.
F The majority of crocodilian is considered to go into aestivation during the dry season. In a six-year study by Kennett and Christian, the King Crocodiles, a species of Australian freshwater crocodiles, spent nearly four months a year underground without access to water resources. Doubly labelled water was applied to detect field metabolic rates and water flux, and during some years, plasma fluid samples were taken once a month to keep track of the effects of aestivation regarding the accumulation of nitrogenous wastes and electrolyte concentrations.
G The study discovered that the crocodiles' metabolic engines function slowly, creating waste and exhausting water and fat reserves. Waste is stored in the urine, becoming more and more concentrated. Nevertheless, the concentration of waste products in blood doesn't fluctuate much, allowing the crocodiles to carry on their normal functions. Besides, even though the crocodiles lost water reserves and body weight when underground, the losses were proportional; upon emerging, the aestivating animals had no dehydration and displayed no other harmful effects such as a slowed-down growth rate. The two researchers reckon that this capacity of crocodiles to get themselves through the harsh times and the long starvation periods is sure to be the answer to the crocodilian line's survival throughout history.
Questions
Questions 15–21 Matching Headings
Reading Passage 2 has seven paragraphs, A-G.
Choose the correct heading for each paragraph from the list of headings below.
Write the correct number, i-xi.
i. The favourable feature in the impact of a drought
ii. A unique finding that was recently achieved
iii. Slow metabolism which makes crocodile a unique reptile
iv. The perfectly designed body for a great land roamer
v. Shifting eating habits and food intake
vi. A project on a special mechanism
vii. Regulating body temperature by the surrounding environment
viii. Underwater aid in body structure offered to a successful predator
ix. A historical story for the supreme survivors
x. What makes the crocodile the fastest running animal on land
xi. The competition between the crocodiles and other animals
Questions 22–27 Summary Completion
Complete the summary below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
Aestivation
In many places inhabited by crocodilians, most types of crocodiles have evolved a successful scheme to survive in the drought brought by a 22. According to Kennett and Christian's six-year study of Australian freshwater crocodiles' aestivation, they found aestivating crocodiles spent around 23 of the year and had no access to 24. The amount of water in the body declined proportionately with 25; thus there is no sign of 26 and other health-damaging impact on the crocodiles even after an aestivation period. This super capacity helps crocodiles endure the tough drought without slowing their speed of 27.
Answers & Explanations Summary
| # | Answer | Evidence | Explanation |
|---|---|---|---|
| Q15 | ix | They witnessed the rise and fall of the dinosaurs, which once ruled the planet, and even the 65 million years of alleged mammalian dominance didn't wipe them off | Excerpt/Passage Explanation: The passage says that crocodiles saw dinosaurs become powerful and then disappear. It also says that even when mammals were thought to be the most important animals for millions of years, crocodiles still managed to live and were not destroyed. Answer Explanation: The answer means that Paragraph A tells a long story about how crocodiles have lived for a very, very long time and how good they are at surviving. Reason For Correctness: The correct answer is 'ix. A historical story for the supreme survivors' because Paragraph A talks about how crocodiles have lived for 200 million years. It explains that they survived when other animals, like dinosaurs, disappeared. The paragraph highlights their ability to adapt and continue living throughout history, showing they are 'supreme survivors' because they kept going through many big changes on Earth. |
| Q16 | iv | The first crocodile-like ancestors came into existence approximately 230 million years ago, and they had many of the features which make crocodiles natural and perfect stealth hunters: streamlined body, long tail, protective armour and long jaws. They are born with four short, webbed legs, but this does not mean that their capacity to move on the ground shall ever be underestimated. When they move, they are so fast that you won't even have any chance to try making the same mistake again by getting too close, especially when they're hunting | Excerpt/Passage Explanation: The passage explains that early crocodiles had good body parts like a smooth body, long tail, and strong skin, which made them great hunters. It then says that even though they have short legs, they can move very, very fast on land, so you should not think they are slow. Answer Explanation: The answer, 'iv', means that Paragraph B is mostly about how crocodiles have a body that works very well for moving on land. Reason For Correctness: The correct answer is 'iv. The perfectly designed body for a great land roamer' because Paragraph B describes the physical features of crocodiles and their ancestors, calling them 'natural and perfect stealth hunters' with a 'streamlined body, long tail, protective armour and long jaws'. It also highlights their surprising ability to move quickly 'on the ground', stating their 'capacity to move on the ground shall ever be underestimated' and that 'they are so fast'. These details explain their well-suited body and their effectiveness as 'land roamers'. |
| Q17 | iii | Compared with mammals and birds, crocodiles have a slower metabolism, which makes them less vulnerable to food shortage. In the most extreme case, a crocodile can slow its metabolism down even further, to the point that it would survive without food for a whole year, enabling them to outlive mammals in relatively volatile environments | Excerpt/Passage Explanation: The passage says that crocodiles use energy in their bodies more slowly than animals like mammals and birds. This means they are less likely to be harmed if there isn't enough food. It also says that a crocodile can slow down its body's energy use even more, so it can live for a whole year without eating. This helps them stay alive longer than mammals in places where conditions change a lot. Answer Explanation: The answer is 'iii', which means the heading for Paragraph C is about crocodiles having a slow way their bodies use energy, which makes them special among reptiles. Reason For Correctness: The correct answer is 'iii. Slow metabolism which makes crocodile a unique reptile' because Paragraph C mostly explains how crocodiles' bodies use energy slowly. It talks about their 'slower metabolism' and how this helps them live longer without food than other animals like mammals and birds. This special ability to slow down their body's energy use and survive without eating for a very long time is what makes them unique, especially in tough environments. |
| Q18 | v | Crocodiles are successful because they are capable of switching feeding methods. It chases after fish and snatches birds at the water surface, hides in the waterside bushes in anticipation of a gazelle, and when the chance to ambush presents itself, the crocodile dashes forward, knocks the animal out with its powerful tail and then drags the prey into the water to drown | Excerpt/Passage Explanation: The passage says that crocodiles are good at catching food because they can change how they hunt. It then gives examples: they can hunt small fish and birds in the water, or they can hide and wait to catch bigger animals like a gazelle on land, using their tail to hit them and then taking them into the water. This shows they have many ways of getting their food. Answer Explanation: The answer means that the correct main idea for Paragraph D is about how crocodiles change the way they eat and what kind of food they catch. Reason For Correctness: The correct answer is 'v. Shifting eating habits and food intake' because Paragraph D explains how crocodiles adjust their hunting strategies and the types of food they consume. The paragraph explicitly states that crocodiles are good hunters because they can 'switching feeding methods' to catch different kinds of prey, like fish, birds, or gazelles. This shows their ability to change their eating habits and what they eat. |
| Q19 | i | For instance, many crocodiles can protect themselves by digging holes and covering themselves in mud, waiting for months without consuming any food or water until the rains finally return | Excerpt/Passage Explanation: The passage says that crocodiles can keep themselves safe during dry times. They do this by digging holes and hiding in mud. They can stay there for many months without eating or drinking until the rain comes back. Answer Explanation: The answer means that Paragraph E talks about something good or helpful that happens because of dry weather (a drought). Reason For Correctness: The correct answer is 'i. The favourable feature in the impact of a drought' because Paragraph E explains how crocodiles can actually protect themselves during dry seasons. It states that even though drought makes it hard for them, this difficult situation actually 'allowed reptiles to rule' by showing how they can survive. The paragraph then describes the special way crocodiles 'protect themselves by digging holes and covering themselves in mud, waiting for months without consuming any food or water' during these dry times. This ability to survive without food or water for a long time during a drought is the 'favourable feature' mentioned in the heading. |
| Q20 | vi | In a six-year study by Kennett and Christian, the King Crocodiles, a species of Australian freshwater crocodiles, spent nearly four months a year underground without access to water resources. Doubly labelled water was applied to detect field metabolic rates and water flux, and during some years, plasma fluid samples were taken once a month to keep track of the effects of aestivation regarding the accumulation of nitrogenous wastes and electrolyte concentrations | Excerpt/Passage Explanation: The passage says that some scientists, Kennett and Christian, did a 'six-year study' (a long project or research) on crocodiles. They watched how these crocodiles lived underground for several months each year without water, a special way they survive. The scientists used different tests, like 'doubly labelled water' and 'plasma fluid samples', to understand how this special way of surviving, called 'aestivation', affected their bodies. Answer Explanation: The answer, 'vi', means that this part of the text is about a special plan or study that looks into how something works in a unique way. Reason For Correctness: The correct answer is 'vi. A project on a special mechanism' because Paragraph F describes a 'six-year study by Kennett and Christian' on King Crocodiles. This study, or 'project', investigated how these crocodiles manage to survive for months underground without food or water by entering a state called 'aestivation'. This 'aestivation' is a 'special mechanism' that helps them survive harsh dry seasons. The paragraph details the methods used in this study, confirming it is a description of a research project on a unique survival method. |
| Q21 | ii | The study discovered that the crocodiles' metabolic engines function slowly, creating waste and exhausting water and fat reserves. Waste is stored in the urine, becoming more and more concentrated. Nevertheless, the concentration of waste products in blood doesn't fluctuate much, allowing the crocodiles to carry on their normal functions. Besides, even though the crocodiles lost water reserves and body weight when underground, the losses were proportional; upon emerging, the aestivating animals had no dehydration and displayed no other harmful effects such as a slowed-down growth rate | Excerpt/Passage Explanation: The passage explains that the research found out new things. It discovered that crocodiles' bodies work very slowly, using up water and fat, and storing waste in their urine. But even with concentrated waste, their blood stays normal. It also found that when crocodiles come out of their long sleep, they are not dried out and have not grown slower. These are all the special new things the study learned. Answer Explanation: The answer, 'A unique finding that was recently achieved,' means that the paragraph talks about a new and special discovery that was made not long ago. Reason For Correctness: The correct answer 'ii. A unique finding that was recently achieved' is suitable for Paragraph G because this paragraph specifically reports the 'discoveries' made by the study mentioned in the previous paragraph. It explains what the researchers found out about how crocodiles survive during dry periods, such as their slow metabolism, how they manage waste products, and that they don't get dehydrated. These are presented as new and important results from the research. |
| Q22 | hot season / dry season | In many crocodilian habitats, the hot season brings drought that dries up their hunting grounds, leaving it harder for them to regulate body temperatures | Excerpt/Passage Explanation: The passage explains that in places where crocodiles live, the very warm time of the year causes a period of time with no rain, making the ground dry. This makes it hard for crocodiles to keep their bodies at the right temperature. Answer Explanation: The answer, 'hot season,' means the time of year when it is very warm. This warm period causes a lack of water, which is called a drought. Reason For Correctness: The correct answer is 'hot season' because the passage clearly states that this specific time of year is responsible for causing droughts. Crocodiles have developed a way to survive these droughts, which are 'brought by' the hot season. The passage in section E explains this. |
| Q23 | four months | In a six-year study by Kennett and Christian, the King Crocodiles, a species of Australian freshwater crocodiles, spent nearly four months a year underground without access to water resources | Excerpt/Passage Explanation: The passage says that in a study, a type of crocodile from Australia stayed underground for almost four months every year. They did not have water during this time. Answer Explanation: The answer is 'four months'. This means the crocodiles spent about four months of the year sleeping underground when it was dry. Reason For Correctness: The correct answer is 'four months' because the passage states that the Australian freshwater crocodiles in the study spent approximately this amount of time each year underground. This behavior is part of their aestivation process to survive dry periods. |
| Q24 | water resources | In a six-year study by Kennett and Christian, the King Crocodiles, a species of Australian freshwater crocodiles, spent nearly four months a year underground without access to water resources | Excerpt/Passage Explanation: The passage says that in a study, Australian crocodiles stayed underground for about four months each year. During this time, they could not get any water. Answer Explanation: The answer 'water resources' means that crocodiles did not have any water available to them. Reason For Correctness: The correct answer is 'water resources' because the passage describes a study where crocodiles went underground for several months without any water. The study, conducted by Kennett and Christian, specifically highlights that the crocodiles 'had no access to water resources' during their time underground. |
| Q25 | body weight | Besides, even though the crocodiles lost water reserves and body weight when underground, the losses were proportional; upon emerging, the aestivating animals had no dehydration and displayed no other harmful effects such as a slowed-down growth rate | Excerpt/Passage Explanation: The passage says that crocodiles lose water and their body weight when they are hiding underground. But it also says that they lose both things at the same rate. So, when they come out, they are not dry and do not have problems like slow growth. Answer Explanation: The answer 'body weight' means how heavy an animal's body is. Reason For Correctness: The correct answer is 'body weight' because the passage explains that when crocodiles go into aestivation (a deep sleep), they lose water and their body weight goes down at the same rate. This means they stay healthy and do not get sick or dehydrated. |
| Q26 | dehydration | Besides, even though the crocodiles lost water reserves and body weight when underground, the losses were proportional; upon emerging, the aestivating animals had no dehydration and displayed no other harmful effects such as a slowed-down growth rate | Excerpt/Passage Explanation: The passage explains that even when crocodiles lost water and body weight while hiding underground, it was a fair amount for both. So, when they came out, they were not 'dehydrated' (didn't lose too much water) and didn't show other bad problems like growing slower. Answer Explanation: The answer 'dehydration' means that the crocodiles did not lose too much water from their bodies, which is good for their health. Reason For Correctness: The correct answer is 'dehydration' because the passage states that even though crocodiles lost water during aestivation, this loss was balanced compared to their body weight loss. Therefore, when they came out of aestivation, they showed no signs of 'dehydration' or other bad health effects. |
| Q27 | growth | Besides, even though the crocodiles lost water reserves and body weight when underground, the losses were proportional; upon emerging, the aestivating animals had no dehydration and displayed no other harmful effects such as a slowed-down growth rate | Excerpt/Passage Explanation: The passage states that even though crocodiles lost water and weight while sleeping underground, they were not dry and their growth did not become slower. This means they continued to grow at a normal speed. Answer Explanation: The answer 'growth' means how much the crocodiles grow bigger or change over time. Reason For Correctness: The correct answer is 'growth' because the passage explains that even after a long period of not eating or drinking during aestivation, crocodiles do not show any bad effects, like slower growth. It means their bodies still grow normally. The passage states they had 'no other harmful effects such as a slowed-down growth rate'. |