The harsh conditions in deserts are intolerable for most plants and animals. Despite these conditions, however, many varieties of plants and animals have adapted to deserts in a number of ways. Most plant tissues die if their water content falls too low: the nutrients that feed plants are transmitted by water; water is a raw material in the vital process of photosynthesis; and water regulates the temperature of a plant by its ability to absorb heat and because water vapor lost to the atmosphere through the leaves helps to lower plant temperatures. Water controls the volume of plant matter produced. The distribution of plants within different areas of desert is also controlled by water. Some areas, because of their soil texture, topographical position, or distance from rivers or groundwater, have virtually no water available to plants, whereas others do.
The nature of plant life in deserts is also highly dependent on the fact that they have to adapt to the prevailing aridity. There are two general classes of vegetation: long-lived perennials, which may be succulent (water-storing) and are often dwarfed and woody, and annuals or ephemerals, which have a short life cycle and may form a fairly dense stand immediately after rain.
The ephemeral plants evade drought. Given a year of favorable precipitation, such plants will develop vigorously and produce large numbers of flowers and fruit. This replenishes the seed content of the desert soil. The seeds then lie dormant until the next wet year, when the desert blooms again.
The perennial vegetation adjusts to the aridity by means of various avoidance mechanisms. Most desert plants are probably best classified as xerophytes. They possess drought-resisting adaptations: loss of water through the leaves is reduced by means of dense hairs covering waxy leaf surfaces, by the closure of pores during the hottest times to reduce water loss, and by the rolling up or shedding of leaves at the beginning of the dry season. Some xerophytes, the succulents (including cacti), store water in their structures. Another way of countering drought is to have a limited amount of mass above ground and to have extensive root networks below ground. It is not unusual for the roots of some desert perennials to extend downward more than ten meters. Some plants are woody in type —an adaptation designed to prevent collapse of the plant tissue when water stress produces wilting. Another class of desert plant is the phreatophyte. These have adapted to the environment by the development of long taproots that penetrate downward until they approach the assured water supply provided by groundwater. Among these plants are the date palm, tamarisk, and mesquite. They commonly grow near stream channels, springs, or on the margins of lakes.
Animals also have to adapt to desert conditions, and they may do it through two forms of behavioral adaptation: they either escape or retreat. Escape involves such actions as aestivation, a condition of prolonged dormancy, or torpor, during which animals reduce their metabolic rate and body temperature during the hot season or during very dry spells.
Seasonal migration is another form of escape, especially for large mammals or birds. The term retreat is applied to the short-term escape behavior of desert animals, and it usually assumes the pattern of a daily rhythm. Birds shelter in nests, rock overhangs, trees, and dense shrubs to avoid the hottest hours of the day, while mammals like the kangaroo rat burrow underground.
Some animals have behavioral, physiological, and morphological (structural) adaptations that enable them to withstand extreme conditions. For example, the ostrich has plumage that is so constructed that the feathers are long but not too dense. When conditions are hot, the ostrich erects them on its back, thus increasing the thickness of the barrier between solar radiation and the skin. The sparse distribution of the feathers, however, also allows considerable lateral air movement over the skin surface, thereby permitting further heat loss by convection. Furthermore, the birds orient themselves carefully with regard to the Sun and gently flap their wings to increase convection cooling.
Paragraph 1: The harsh conditions in deserts are intolerable for most plants and animals. Despite these conditions, however, many varieties of plants and animals have adapted to deserts in a number of ways. Most plant tissues die if their water content falls too low: the nutrients that feed plants are transmitted by water; water is a raw material in the vital process of photosynthesis; and water regulates the temperature of a plant by its ability to absorb heat and because water vapor lost to the atmosphere through the leaves helps to lower plant temperatures. Water controls the volume of plant matter produced. The distribution of plants within different areas of desert is also controlled by water. Some areas, because of their soil texture, topographical position, or distance from rivers or groundwater, have virtually no water available to plants, whereas others do.
1: According to paragraph 1, water provides all of the following essential functions for plants EXCEPT
○ improving plants’ ability to absorb sunlight
○ preventing plants from becoming overheated
○ transporting nutrients
○ serving as a raw material for photosynthesis
Paragraph 2: The nature of plant life in deserts is also highly dependent on the fact that they have to adapt to the prevailing aridity. There are two general classes of vegetation: long-lived perennials, which may be succulent (water-storing) and are often dwarfed and woody, and annuals or ephemerals, which have a short life cycle and may form a fairly dense stand immediately after rain.
Paragraph 3: The ephemeral plants evade drought. Given a year of favorable precipitation, such plants will develop vigorously and produce large numbers of flowers and fruit. This replenishes the seed content of the desert soil. The seeds then lie dormant until the next wet year, when the desert blooms again.
2: Paragraph 3 suggests that during a dry year ephemerals
○ produce even more seeds than in a wet year
○ do not sprout from their seeds
○ bloom much later than in a wet year
○ are more plentiful than perennials
3: How is paragraph 2 related to paragraph 3?
○ Paragraph 2 provides a general description of desert plants, and paragraph 3 provides a scientific explanation for these observations.
○ Paragraph 2 divides desert plants into two categories, and paragraph 3 provides further information about one of these categories.
○ Paragraph 2 proposes one way of dividing desert plants into categories, and paragraph 3 explains one problem with this method of classification.
○ Paragraph 2 discusses two categories of desert plants, and paragraph 3 introduces a third category of plants.
4: In saying that ephemerals will develop “vigorously" when there is favorable precipitation, the author means that their development will be
○ sudden
○ early
○ gradual
○ strong and healthy
Paragraph 4: The perennial vegetation adjusts to the aridity by means of various avoidance mechanisms. Most desert plants are probably best classified as xerophytes. They possess drought-resisting adaptations: loss of water through the leaves is reduced by means of dense hairs covering waxy leaf surfaces, by the closure of pores during the hottest times to reduce water loss, and by the rolling up or shedding of leaves at the beginning of the dry season. Some xerophytes, the succulents (including cacti), store water in their structures. Another way of countering drought is to have a limited amount of mass above ground and to have extensive root networks below ground. It is not unusual for the roots of some desert perennials to extend downward more than ten meters. Some plants are woody in type —an adaptation designed to prevent collapse of the plant tissue when water stress produces wilting. Another class of desert plant is the phreatophyte. These have adapted to the environment by the development of long taproots that penetrate downward until they approach the assured water supply provided by groundwater. Among these plants are the date palm, tamarisk, and mesquite. They commonly grow near stream channels, springs, or on the margins of lakes.
5: The word “countering” in the passage is closest in meaning to
○ eliminating
○ making use of
○ acting against
○ experiencing
6: According to paragraph 4, some desert plants with root systems that are extraordinarily well developed have
○ relatively little growth aboveground
○ very leafy aboveground structures
○ non woody plant tissue resistant to wilting
○ water stored within their roots
7: The word “assured” in the passage is closest in meaning to
○ pure
○ diminished
○ guaranteed
○ deep
8: What do “the date palm, tamarisk, and mesquite" have in common?
○ They are always found together.
○ They depend on surface water provided by streams, springs, and lakes.
○ They are phreatophytes.
○ Their roots are capable of breaking through hard soils
Paragraph 5: Animals also have to adapt to desert conditions, and they may do it through two forms of behavioral adaptation: they either escape or retreat. Escape involves such actions as aestivation, a condition of prolonged dormancy, or torpor, during which animals reduce their metabolic rate and body temperature during the hot season or during very dry spells.
9: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
○ One way animals escape is by entering a state of extended dormancy, known as aestivation, during the hottest and driest times of year.
○ Animals can escape without using direct action, or aestivation, simply by reducing their metabolic rate and body temperature.
○ The actions that an animal uses to escape are known as aestivation, which sometimes involves a reduction in metabolic rate or body temperature.
○ When the weather is especially hot and dry, an animal may suffer from a condition known as aestivation, at which point the animal needs to escape.
Paragraph 6:Seasonal migration is another form of escape, especially for large mammals or birds. The term retreat is applied to the short-term escape behavior of desert animals, and it usually assumes the pattern of a daily rhythm. Birds shelter in nests, rock overhangs, trees, and dense shrubs to avoid the hottest hours of the day, while mammals like the kangaroo rat burrow underground.
10: It can be inferred from paragraph 6 that all of the places desert animals retreat to
○ provide shade from the sun
○ sometimes become crowded
○ are places where supplies of food are plentiful
○ leave the animals vulnerable to predators
Paragraph 7: Some animals have behavioral, physiological, and morphological (structural) adaptations that enable them to withstand extreme conditions. For example, the ostrich has plumage that is so constructed that the feathers are long but not too dense. When conditions are hot, the ostrich erects them on its back, thus increasing the thickness of the barrier between solar radiation and the skin. The sparse distribution of the feathers, however, also allows considerable lateral air movement over the skin surface, thereby permitting further heat loss by convection. Furthermore, the birds orient themselves carefully with regard to the Sun and gently flap their wings to increase convection cooling.
11: According to paragraph 7, what special adaptation helps the ostrich cope with hot desert conditions?
○ Each of its feathers is very short and dense.
○ Its wings produce only lateral air movement when flapping.
○ Its feathers are very thickly set on both its back and its wings.
○ It can make its feathers stand up on its back.
Paragraph 1: The harsh conditions in deserts are intolerable for most plants and animals. Despite these conditions, however, many varieties of plants and animals have adapted to deserts in a number of ways. Most plant tissues die if their water content falls too low: the nutrients that feed plants are transmitted by water; water is a raw material in the vital process of photosynthesis; and water regulates the temperature of a plant by its ability to absorb heat and because water vapor lost to the atmosphere through the leaves helps to lower plant temperatures. ■Water controls the volume of plant matter produced. ■The distribution of plants within different areas of desert is also controlled by water. ■Some areas, because of their soil texture, topographical position, or distance from rivers or groundwater, have virtually no water available to plants, whereas others do.■
12: Look at the four squares [■] that indicate where the following sentence could be added to the passage.
The increase in reward still did not attract young people to this hard life, and convicted criminals and slaves were pressed into services
Where would the sentence best fit?
這道題是錯題，請大家先不要關注。
13: Directions: Select from the seven phrases below the two phrases that correctly characterize special adaptations found primarily in desert annuals and the three phrases that correctly characterize special adaptations found primarily in desert perennials. Select each phrase you select in the appropriate column of the table. This question is worth 3 points.
Adaptations of Annuals
Adaptations of Perennials
Four of the phrases will NOT be used.
Answer Choices
○ Woody structures
○ Explosive growth in wet years
○ Long, thin, shallow roots
○ Storage of water in plant tissue
○ Minimization of the amount of water used for photosynthesis
○ Short life cycle
○ Leaves designed to minimize water loss
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答案：
1. ○ 1
2. ○ 2
3. ○ 2
4. ○ 4
5. ○ 3
6. ○ 1
7. ○ 3
8. ○ 3
9. ○ 1
10. ○ 1
11. ○ 4
12. ○ 2
13. ANNUALS:
○ Explosive growth in wet years
○ Short life cycle
PERENNIALS:
○ Woody structures
○ Storage of water in plant tissue
○ Leaves designed to minimize water loss
沙漠中的嚴酷環(huán)境對于大部分動植物來說都是難以忍受的。然而，盡管如此，還是有多樣的動植物通過各種方式最終適應了沙漠環(huán)境。如果水含量過低，大部分植物組織會死亡；植物所汲取的養(yǎng)分是通過水分來傳輸?shù)�；水分也是光合作用這個關鍵過程中的成分；同時，水分通過吸收熱量來調節(jié)植物體的溫度，因為水蒸氣通過葉片蒸騰到空氣中的過程可以幫助植物降低溫度。水分控制著植物物質的產(chǎn)出量。沙漠中不同地區(qū)的植物的分布也受水分的控制。在有些地區(qū)，因為土質、地形位置或者與河流或地下水的距離等因素，幾乎沒有水分提供給植物，而其他一些地方則相反。
沙漠中植物的特征很大程度上取決于它們對這種普遍干旱條件的適應程度。沙漠地區(qū)的植物大致可以分為兩類：壽命較長的多年生植物，這類植物一般都是多肉植物（可以儲水），經(jīng)常是比較矮小的木本植物；以及一年生或壽命更短的植物，這類植物生命周期短，可能在降雨后快速而密集地形成。
那些壽命短的植物“|躲避”干旱。在一個降雨比較充足的年份中，這類植物會迅速生長，并且會大量地開花結果。如此一來，這類植物的種子會遍布沙漠。這些種子會靜靜地休眠直到下一個雨量較充沛的年份，再次在沙漠中綻放。
多年生植物會采用各種躲避機制以適應干旱。大部分的沙漠植物可能最好都被歸類為旱生植物。這類植物進化出了抗旱適應機制：覆蓋在蠟質葉子層表面的濃密的絨毛,在溫度最高的時候閉合氣孔,在干旱季初期卷起或脫落葉片都可以減少經(jīng)過葉片的水分的流失。有些旱生植物在植物組織中貯存水分，如多肉植物（包括仙人掌）。另一種抵抗干旱的方法是抑制植物地上部分的生長，轉而發(fā)展廣泛的地下根系網(wǎng)絡。有些多年生沙漠植物的根系可以向下延伸10米多深，這種情況（在沙漠中）并不少見。有些植物是木本植物，這種適應機制可以防止因水壓（下降）產(chǎn)生萎蔫而引起的植物細胞解體。另一類沙漠植物類別則是地下水濕生植物。這類植物通過繁衍長的主根來適應環(huán)境，這些主根可以向下穿透直達地下水提供的充足水源。這類植物包括棗椰樹、檉柳以及牧豆樹屬的一些灌木。這類植物通常情況下沿溪流，河道或者是湖泊邊緣分布。
動物也必須要適應沙漠環(huán)境，它們通過兩種行為模式來適應沙漠：逃離或撤退。逃離包括一些類似于夏眠這樣的行為，這一行為可以使得動物們在酷暑難耐或炎熱季節(jié)依靠長期的休眠或蟄伏來降低它們的新陳代謝速率和體溫。
季節(jié)性遷徙是逃離行為的另一種表現(xiàn)方式，特別是對于大型哺乳類動物和鳥類而言。撤退一詞是用于形容短期的沙漠動物逃離行為的，而且這通常被認為是一種日常性的節(jié)律模式。鳥類在巢穴、巖石懸垂處、樹叢以及茂密的灌木叢中尋找庇護以躲避一天當中最熱的那幾個鐘頭，而像更格盧鼠這樣的哺乳動物則選擇藏身于地下的洞穴中。
有些動物還具有行為學、生理學以及形態(tài)學（結構）上的適應機制，以確保它們可以抵抗極端環(huán)境。例如，鴕鳥的羽毛具有這樣的結構特征：毛很長但不太濃密。當氣溫變熱時，鴕鳥便會豎起背上的羽毛，因此增加太陽輔射與嬌嫩皮膚之間的屏障的厚度。然而，這些稀疏排列的羽毛同時也確保了皮膚表面橫向空氣流動的進行，因此通過對流達到散熱的效果。此外，鴕鳥會根據(jù)太陽的位置謹慎調整自己的方向，輕輕拍打翅膀以增加對流的降溫效果。
