Table of Contents
BEST IELTS Academic Reading Test 224
IELTS ACADEMIC READING TEST 224 – PASSAGE – 3
IELTS ACADEMIC READING TEST – 224
READING PASSAGE – 3
Owl Secrets
A. It always appeared to fly in the face of logic. But now, the biological secrets that allow owls to rotate their heads without cutting off their blood supply have finally been unraveled. Scientists have discovered four major adaptations in owls designed to prevent injury when the animals rotate their overly large heads by up to 270 degrees.
B. The study found that the birds’ unique bone structures and vascular systems let them move with increased flexibility. Scientists at John Hopkins University School of Medicine in the US studied snowy, barred and great horned owls y after their deaths from natural causes. They found that the vertebral artery enters the neck higher than in other birds, creating more slack. Unlike humans, owls were found to have small vessel connections between the carotid and vertebral arteries, allowing the blood to be exchanged between the two blood vessels. This creates an uninterrupted blood flow to the brain, even if one route is blocked during extreme neck rotation.
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C. The adaptation gives the birds a huge range of vision without having to move their bodies and arouses detection by prey. The lack of similar adaptations in humans could explain why humans are more vulnerable to neck injury, the experts concluded. When humans attempt sudden and violent twists of their neck they risk damaging the lining of their blood vessels, which can result in a fatal blockage or stroke.
Study senior investigator Doctor Philippe Gailloud, said: ‘Until now, brain imaging specialists like me who deal with human injuries caused by trauma to arteries in the head and neck have always been puzzled as to why rapid, twisting neck movements did not leave thousands of owls lying dead on the forest floor from stroke. ‘The carotid and vertebral arteries in the neck of most animals – including owls and humans – are very fragile and highly susceptible to even minor tears of the vessel lining.
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D. To solve the puzzle, the researchers studied the bone and blood vessel structures in the heads and necks of the birds. An injectable contrast dye was used to highlight the birds’ blood vessels, which were then dissected, drawn and scanned to allow detailed analysis.
E. The most striking finding came after researchers injected dye into the owls’ arteries, mimicking blood flow, and manually turned the animals’ heads. They found that when they turned the heads, the blood vessels below the jaw bone expanded as more dye entered, creating pools of blood capable of maintaining the energy supply to the brain and eyes. They showed that the big carotid arteries, instead of being on the side of the neck as in humans, are carried close to the center of rotation just in front of the spine.
As a consequence, these arteries experience much less twisting and turning. The potential for damage is therefore greatly reduced. This conträsted starkly with human anatomical ability, where arteries generally tend to get smaller and smaller, and do not balloon out as they branch out. This creates the risk of clotting after sudden neck movements such as whiplash.
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F. Researchers say these contractile blood reservoirs act as a trade-off, allowing birds to pool blood to meet the energy needs of their large brains and eyes, while they rotate their heads. The supporting vascular network, with its many interconnections and adaptations, helps minimize any interruption in blood flow. The study results demonstrate what physical properties are needed to allow such extreme head movements, and explain why injuries sustained from treatments that involve manipulating bones with the hands such as chiropractic therapy can have such serious consequences for humans.
Dr Gailloud added: ‘Our new study results show precisely what morphological adaptations are needed to handle such head gyrations and why humans are so vulnerable to bone injury from chiropractic therapy. Extreme manipulations of the human head are really dangerous because we lack so many of the vessel-protecting features seen in owls.’
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G. Medical illustrator Fabian de Kok-Mercado said: ‘In humans, the vertebral artery really hugs the brains and eyes, while they rotate their heads. The supporting vascular network, with its many interconnections and adaptations, helps minimize any interruption in blood flow. The study results demonstrate what physical properties are needed to allow such extreme head movements, and explain why injuries sustained from treatments that involve manipulating bones with the hands such as chiropractic therapy can have such serious consequences for humans.
Dr Gailloud added: ‘Our new study results show precisely what morphological adaptations are needed to handle such head gyrations and why humans have hollow cavities in the neck. But this is not the case in owls, whose structures are specially adapted to allow for greater arterial flexibility and movement.’ It is a powerful adaptive trait, but it is not unique. Plenty of birds have a similar ability to look behind them. Red tailed hawks for example are almost as flexible as their nocturnal cousins. ‘There are lots of advantages to being able to look over your shoulder and see something coming – if you’re trying to avoid predators or detect prey’, he added.
IELTS Academic Reading Test
Questions 27-34
Complete the summary using the list of words and phrases A-M below.
Write the correct letter, A-M in boxes 27-34 on your answer sheet.
NB: You may use any letter more than once
How can owls rotate their heads by (27)……… 270 degrees? The many small bones that make up the neck and spine enable them to achieve (28)……… movement. A research team has discovered that in (29)……… , their vascular network has adapted to make the rotation possible. Owls’ carotid arteries are (30)……… the spine, at the centre of rotation. This means the arteries endure (31)……… the strain when the head is turned.
In addition, the vessels (32)……… their heads can expand, creating reservoirs of blood to supply the brain when the head is turned. And the cavities in the neck vertebrae, through which the vessels pass, are extremely (33)……… giving the vessels space to move around when twisted. All this is necessary because their eyes can’t move: owls can only look (34)……… ahead.
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List of word/ phrases:
A. flexible
B. as much as
C. at the base of
D. in front of
E. intense
F. limited
G. far less
H. multiple
I. in excess of
J. to the side of
K. various ways
L. large
M. straight
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Questions 35-40
Complete each sentence with the correct ending, A-H below. Write the correct letter, A-H in boxes 35-40 on your answer sheet.
35. The bone structure and circulatory system of owls has evolved in order to
36. Humans’ arteries tend to
37. Scientists injected dye into the blood vessels of dead owls in order to 38. When humans attempt sudden twists of their neck they are more likely to
39. The back;up arteries of owls are designed to
40. Owls have a huge range of vision which enables them to
A. collect any excess blood created in the process of turning.
B. cope with their very large heads.
C. damage the lining of their blood vessels.
D. decrease in size.
E. make them lighter.
F. mimic natural blood flow.
G. offer a fresh supply of nutrients when blood vessels get closed off.
H. avoid detection by predators or to find prey.
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ANSWERS ARE BELOW
IELTS Academic Reading Test
ANSWERS
27. B
28. A
29. K
30. D
31. G
32. C
33. L
34. M
35. B
36. D
37. F
38. C
39. G
40. H
IELTS Academic Reading Test