Autumn leaves – Giải đề IELTS Reading chi tiết
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Bài đọc Autumn leaves
Canadian writer Jay Ingram investigates the mystery of why leaves turn red in the fall
A One of the most captivating natural events of the year in many areas throughout North America is the turning of the leaves in the fall. The colours are magnificent, but the question of exactly why some trees turn yellow or orange, and others red or purple, is something which has long puzzled scientists.
B Summer leaves are green because they are full of chlorophyll, the molecule that captures sunlight converts that energy into new building materials for the tree. As fall approaches in the northern hemisphere, the amount of solar energy available declines considerably. For many trees – evergreen conifers being an exception – the best strategy is to abandon photosynthesis* until the spring. So rather than maintaining the now redundant leaves throughout the winter, the tree saves its precious resources and discards them. But before letting its leaves go, the tree dismantles their chlorophyll molecules and ships their valuable nitrogen back into the twigs. As chlorophyll is depleted, other colours that have been dominated by it throughout the summer begin to be revealed. This unmasking explains the autumn colours of yellow and orange, but not the brilliant reds and purples of trees such as the maple or sumac.
C The source of the red is widely known: it is created by anthocyanins, water-soluble plant pigments reflecting the red to blue range of the visible spectrum. They belong to a class of sugar-based chemical compounds also known as flavonoids. What’s puzzling is that anthocyanins are actually newly minted, made in the leaves at the same time as the tree is preparing to drop them. But it is hard to make sense of the manufacture of anthocyanins – why should a tree bother making new chemicals in its leaves when it’s already scrambling to withdraw and preserve the ones already there?
D Some theories about anthocyanins have argued that they might act as a chemical defence against attacks by insects or fungi, or that they might attract fruit-eating birds or increase a leafs tolerance to freezing. However there are problems with each of these theories, including the fact that leaves are red for such a relatively short period that the expense of energy needed to manufacture the anthocyanins would outweigh any anti-fungal or anti-herbivore activity achieved.* photosynthesis: the production of new material from sunlight, water and carbon dioxide.
E It has also been proposed that trees may produce vivid red colours to convince herbivorous insects that they are healthy and robust and would be easily able to mount chemical defences against infestation. If insects paid attention to such advertisements, they might be prompted to lay their eggs on a duller, and presumably less resistant host. The flaw in this theory lies in the lack of proof to support it. No one has as yet ascertained whether more robust trees sport the brightest leaves, or whether insects make choices according to colour intensity.
F Perhaps the most plausible suggestion as to why leaves would go to the trouble of making anthocyanins when they’re busy packing up for the winter is the theory known as the ‘light screen’ hypothesis. It sounds paradoxical, because the idea behind this hypothesis is that the red pigment is made in autumn leaves to protect chlorophyll, the light-absorbing chemical, from too much light. Why does chlorophyll need protection when it is the natural world’s supreme light absorber? Why protect chlorophyll at a time when the tree is breaking it down to salvage as much of it as possible?
G Chlorophyll, although exquisitely evolved to capture the energy of sunlight, can sometimes be overwhelmed by it, especially in situations of drought, low temperatures, or nutrient deficiency. Moreover, the problem of oversensitivity to light is even more acute in the fall, when the leaf is busy preparing for winter by dismantling its internal machinery. The energy absorbed by the chlorophyll molecules of the unstable autumn leaf is not immediately channelled into useful products and processes, as it would be in an intact summer leaf. The weakened fall leaf then becomes vulnerable to the highly destructive effects of the oxygen created by the excited chlorophyll molecules.
H Even if you had never suspected that this is what was going on when leaves turn red, there are clues out there. One is straightforward: on many trees, the leaves that are the reddest are those on the side of the tree which gets most sun. Not only that, but the red is brighter on the upper side of the leaf. It has also been recognised for decades that the best conditions for intense red colours are dry, sunny days and coo nights, conditions that nicely match those that make leaves susceptible to excess light. And finally, trees such as maples usually get much redder the more north you travel in the northern hemisphere. It’s colder there, they’re more stressed, their chlorophyll is more sensitive and it needs more sunblock.
I What is still not fully understood, however, is why some trees resort to producing red pigments while others don’t bother, and simply reveal their orange or yellow hues. Do these trees have other means at their disposal to prevent overexposure to light in autumn? Their story, though not as spectacular to the eye, will surely turn out to be as subtle and as complex.
Câu hỏi Bài đọc Autumn leaves
Questions 14-18
Reading Passage 204 has nine paragraphs, A-l. Which paragraph contains the following information?
Write the correct letter, A-l, in boxes 14-18 on your answer sheet.
NB You may use any letter more than once.
Questions 19-22 Complete the notes below. Choose ONE WORD ONLY from the passage for each answer. Write your answers in boxes 19-22 on your answer sheet.
Why believe the ‘light screen’ hypothesis?
• The most vividly coloured red leaves are found on the side of the tree facing the 19. .
• The 20. surfaces of leaves contain the most red pigment.
• Red leaves are most abundant when daytime weather conditions are 21. and sunny.
• The intensity of the red colour of leaves increases as you go further 22. .
Questions 23-25
Do the following statements agree with the information given in Reading Passage 204?
In boxes 23-25 on your answer sheet, write
TRUE if the statement agrees with the information
FALSE if the statement contradicts the information
NOT GIVEN if there is no information on this
Question 26
Choose the correct letter A, B, C or D. Write the correct letter in box 26 on your answer sheet.
For which of the following questions does the writer offer an explanation?
Điểm số của bạn là % - đúng / câu
Giải thích chi tiết
Questions 14 – 18: Dạng MATCHING HEADINGS Cách làm:
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14. a description of the substance responsible for the red colouration of leaves Câu hỏi đề cập đến là việc vị trí của mô tả về chất tạo nên màu đỏ của lá nằm ở đoạn nào. Thông tin đó nằm ở đoạn C, cụ thể là: Màu đỏ được tạo ra bởi anthocyanins, sắc tố thực vật tan trong nước phản chiếu ánh sáng từ đỏ đến xanh lam. → Đáp án là C | Đoạn C The source of the red is widely known: it is created by anthocyanins, water-soluble plant pigments reflecting the red to blue range of the visible spectrum. |
15. the reason why trees drop their leaves in autumn Câu hỏi đề cập đến vị trí nào trong bài nói về lý do tại sao cây rụng lá vào mùa thu. Thông tin nằm ở đoạn B, nó chỉ ra rằng hầu hết các cây, trừ cây lá kim thường xanh, ngừng quang hợp vào mùa đông và rụng lá để tiết kiệm tài nguyên. → Đáp án là B | Đoạn B For many trees – evergreen conifers being an exception – the best strategy is to abandon photosynthesis* until the spring. So rather than maintaining the now redundant leaves throughout the winter, the tree saves its precious resources and discards them. |
16. some evidence to confirm a theory about the purpose of the red leaves Câu hỏi muốn tìm vị trí của một số bằng chứng để xác nhận một lý thuyết về mục đích của lá đỏ. Trong đoạn H, thông tin chỉ ra ngay cả khi ta chưa từng nghĩ rằng đây là điều xảy ra khi lá chuyển sang màu đỏ, vẫn có những dấu hiệu rõ ràng. → Đáp án là H | Đoạn H Even if you had never suspected that this is what was going on when leaves turn red, there are clues out there. |
17. an explanation of the function of chlorophyll Câu hỏi đề cập đến vị trí nằm ở đoạn nào của lời giải thích về chức năng của diệp lục. Trong đoạn B, ta được biết phân tử chlorophyll giúp hấp thụ ánh sáng và chuyển hóa năng lượng thành vật liệu cho cây -> tạo màu xanh cho lá cây. → Đáp án là B | Đoạn B Summer leaves are green because they are full of chlorophyll, the molecule that captures sunlight converts that energy into new building materials for the tree. |
18. a suggestion that the red colouration in leaves could serve as a warning signal. Câu hỏi đề cập về vị trí trong bài của một gợi ý rằng màu đỏ ở lá có thể đóng vai trò như một tín hiệu cảnh báo. Thông tin đoạn E cho thấy màu đỏ có thể là cách cây “quảng cáo” sức khỏe tốt để xua đuổi côn trùng, khiến chúng chọn cây yếu hơn làm nơi đẻ trứng. → Đáp án là C | Đoạn E It has also been proposed that trees may produce vivid red colours to convince herbivorous insects that they are healthy and robust and would be easily able to mount chemical defences against infestation. If insects paid attention to such advertisements, they might be prompted to lay their eggs on a duller, and presumably less resistant host. |
Questions 19 – 22: Dạng SENTENCE COMPLETION Cách làm:
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The most vividly coloured red leaves are found on the side of the tree facing the 19…………………. . Từ cần điền vào có thể là một danh từ do đứng sau mạo từ “the”. Trên nhiều loại cây, những chiếc lá đỏ nhất là những chiếc lá ở phía cây nhận được nhiều ánh nắng nhất. → Đáp án là sun | Đoạn H One is straightforward: on many trees, the leaves that are the reddest are those on the side of the tree which gets most sun. |
The 20…………………. surfaces of leaves contain the most red pigment. Từ cần điền vào có thể là một danh từ do đứng sau mạo từ “the”. Màu đỏ sáng hơn ở mặt trên của lá. → Đáp án là upper | Đoạn H Not only that, but the red is brighter on the upper side of the leaf. |
Red leaves are most abundant when daytime weather conditions are 21…………………. and sunny. Từ cần điền vào có thể là một tính từ do đứng trước “and” và sau “and” là tính từ “sunny”. Trong nhiều thập kỷ, người ta cũng đã công nhận rằng điều kiện tốt nhất cho màu đỏ đậm là những ngày khô, nắng và đêm mát mẻ, những điều kiện phù hợp với điều kiện khiến lá cây dễ bị ảnh hưởng bởi ánh sáng quá mức. → Đáp án là dry | Đoạn H It has also been recognised for decades that the best conditions for intense red colours are dry, sunny days and cool nights, conditions that nicely match those that make leaves susceptible to excess light. |
The intensity of the red colour of leaves increases as you go further 22…………………. . Từ cần điền vào có thể là một danh từ do đứng sau tính từ “further”. Các loại cây như cây thích thường chuyển sang màu đỏ hơn khi bạn đi về phía bắc ở bán cầu bắc. → Đáp án là north | Đoạn H And finally, trees such as maples usually get much redder the more north you travel in the northern hemisphere. |
Questions 23 – 25: Dạng TRUE/FALSE/NOT GIVEN Cách làm:
Chọn đáp án bằng cách lần lượt trả lời 2 câu hỏi:
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→ Đáp án là FALSE | Đoạn F […] because the idea behind this hypothesis is that the red pigment is made in autumn leaves to protect chlorophyll, the light-absorbing chemical, from too much light. |
24. The ‘light screen’ hypothesis would initially seem to contradict what is known about chlorophyll.
→ Đáp án là TRUE | Đoạn F It sounds paradoxical, because the idea behind this hypothesis is that the red pigment is made in autumn leaves to protect chlorophyll, the light-absorbing chemical, from too much light. |
25. Leaves which turn colours other than red are more likely to be damaged by sunlight.
→ Đáp án là NOT GIVEN | Đoạn B As chlorophyll is depleted, other colours that have been dominated by it throughout the summer begin to be revealed. |
Question 26: Dạng Global MCQ Cách làm:
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For which of the following questions does the writer offer an explanation? | |
B how leaves turn orange and yellow in autumn Nhận xét:
Cụ thể: Theo thông tin của bài đọc, trước khi rụng, cây sẽ phá vỡ các phân tử chlorophyll trong lá và chuyển lượng nitơ quý giá của chúng trở lại cành cây. Khi chlorophyll cạn kiệt, các màu sắc khác, vốn bị chi phối bởi chlorophyll suốt mùa hè, bắt đầu lộ ra. => Điều này giải thích màu vàng và cam của mùa thu, nhưng không giải thích được màu đỏ và tím rực rỡ của các loại cây như phong hay sumac. Điều này ĐÚNG với thông tin trong đáp án B. → Đáp án B là chính xác | Đoạn B But before letting its leaves go, the tree dismantles their chlorophyll molecules and ships their valuable nitrogen back into the twigs. As chlorophyll is depleted, other colours that have been dominated by it throughout the summer begin to be revealed. This unmasking explains the autumn colours of yellow and orange, […] |
A why conifers remain green in winter Nhận xét:
Cụ thể Mặc dù bài có đề cập đến việc cây lá kim vẫn xanh vào mùa đông nhưng không có thông tin nào cho thấy có lời giải thích cho việc này. → Đáp án A là NOT GIVEN | Đoạn B For many trees – evergreen conifers being an exception – the best strategy is to abandon photosynthesis* until the spring. |
C how herbivorous insects choose which trees to lay their eggs in Nhận xét:
Cụ thể Mặc dù bài có đề cập đến việc côn trùng ăn cỏ chọn cây để đẻ trứng nhưng không có thông tin nào cho thấy có lời giải thích cho việc chúng chọn như thế nào. → Đáp án A là NOT GIVEN | Đoạn E It has also been proposed that trees may produce vivid red colours to convince herbivorous insects that they are healthy and robust and would be easily able to mount chemical defences against infestation. If insects paid attention to such advertisements, they might be prompted to lay their eggs on a duller, and presumably less resistant host. |
D why anthocyanins are restricted to certain trees Nhận xét:
Cụ thể Không có thông tin đề cập đến điều này. → Đáp án A là NOT GIVEN | |
