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Survival of Plants and Animals in Desert Conditions

沙漠中的恶劣条件对大多数植物和动物来说是无法忍受的。

The harsh conditions in deserts are intolerable for most plants and animals.

然而，尽管有这些条件，许多种类的植物和动物已经以多种方式适应了沙漠。

Despite these conditions, however, many varieties of plants and animals have adapted to deserts in a number of ways.

如果水分含量过低，大多数植物组织就会死亡：植物的营养物质是通过水传播的；水是光合作用的重要原料；水通过吸收热量的能力来调节植物的温度，因为通过叶子蒸发到大气中的水蒸气有助于降低植物的温度。

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.

沙漠不同地区的植物分布也受水的控制。

The distribution of plants within different areas of desert is also controlled by water.

有些地区由于土壤质地、地形位置或与河流或地下水的距离，实际上没有可供植物利用的水，而另一些地区却有。

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.

沙漠中的植物生命也高度依赖于这样一个事实，即它们必须适应普遍的干旱。

The nature of plant life in deserts is also highly dependent on the fact that they have to adapt to the prevailing aridity.

通常有两类植物：寿命较长的多年生植物，它们可能是多汁的（储水的），通常是矮小的和木本的；一年生植物或短生植物，它们的生命周期很短，在雨后可能立即形成相当密集的林区。

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.

如果有一年的良好降水，这些植物将会茁壮成长，结出大量的花朵和果实。

Given a year of favorable precipitation, such plants will develop vigorously and produce large numbers of flowers and fruit.

这就补充了沙漠土壤的种子含量。

This replenishes the seed content of the desert soil.

然后种子休眠，直到下一个潮湿的年份，当沙漠再次恢复生机。

The seeds then lie dormant until the next wet year, when the desert blooms again.

多年生植物通过各种回避机制来适应干旱。

The perennial vegetation adjusts to the aridity by means of various avoidance mechanisms.

大多数沙漠植物可能最适合归类为旱生植物。

Most desert plants are probably best classified as xerophytes.

他们拥有防旱适应性：通过树叶流失的水量得到了减少，这是通过覆盖于蜡状叶表面的浓密绒毛，通过在最热的时候关闭气孔减少水损失和在干旱季节开始时卷起或脱落树叶实现的。

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.

一些旱生植物，多肉植物（包括仙人掌），在它们的结构中储存水分。

Some xerophytes, the succulents (including cacti), store water in their structures.

对付干旱的另一种方法是在地面上有有限数量的植物，在地下有广泛的根系网络。

Another way of countering drought is to have a limited amount of mass above ground and to have extensive root networks below ground.

有些沙漠多年生植物的根向下延伸十多米是很正常的。

It is not unusual for the roots of some desert perennials to extend downward more than ten meters.

有些植物是木本植物，这是一种适应性的设计，以防止植物组织崩溃时，由于水分压力而产生萎蔫。

Some plants are woody in type —an adaptation designed to prevent collapse of the plant tissue when water stress produces wilting.

沙漠植物的另一类是水生植物。

Another class of desert plant is the phreatophyte.

它们通过长主根的生长适应了环境，这些主根向下渗透，直到接近地下水所提供的有保障的供水。

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.

在这些植物中有枣椰树、红柳和牧豆树。

Among these plants are the date palm, tamarisk, and mesquite.

它们通常生长在溪流、泉水或湖泊边缘。

They commonly grow near stream channels, springs, or on the margins of lakes.

动物也必须适应沙漠环境，它们可能通过两种形式的行为适应来做到这一点：它们要么逃跑，要么撤退。

Animals also have to adapt to desert conditions, and they may do it through two forms of behavioral adaptation: they either escape or retreat.

逃跑行为涉及到夏眠，一种延长睡眠的状态，或是麻痹状态，在这种情况下，动物们在炎热的季节或非常干燥的季节里，会降低新陈代谢率和体温。

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.

季节性迁徙是另一种形式的逃避，特别是对大型哺乳动物或鸟类来说。

Seasonal migration is another form of escape, especially for large mammals or birds.

撤退一词用于描述沙漠动物的短期逃跑行为，通常以日常节律的形式出现。

The term retreat is applied to the short-term escape behavior of desert animals, and it usually assumes the pattern of a daily rhythm.

鸟类在巢穴、岩石、树木和茂密的灌木丛中躲避一天中最热的时候，而像长鼻袋鼠这样的哺乳动物则在地下挖洞。

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.

有些动物具有行为上、生理上和形态上（结构上）的适应性，使它们能够承受极端的环境。

Some animals have behavioral, physiological, and morphological (structural) adaptations that enable them to withstand extreme conditions.

例如，鸵鸟的羽毛构造使它的羽毛长而不密。

For example, the ostrich has plumage that is so constructed that the feathers are long but not too dense.

当天气炎热时，鸵鸟会把它们竖在背上，这样就增加了太阳辐射与皮肤之间的屏障厚度。

When conditions are hot, the ostrich erects them on its back, thus increasing the thickness of the barrier between solar radiation and the skin.

然而，羽毛的稀疏分布也允许相当大的侧向空气运动通过皮肤表面，从而允许进一步的热损失对流。

The sparse distribution of the feathers, however, also allows considerable lateral air movement over the skin surface, thereby permitting further heat loss by convection.

此外，鸟类会根据太阳的位置仔细调整方向，轻轻扇动翅膀以增加对流冷却。

Furthermore, the birds orient themselves carefully with regard to the Sun and gently flap their wings to increase convection cooling.

According to paragraph 1, water provides all of the following essential functions for plants EXCEPT

Paragraph 3 suggests that during a dry year ephemerals

How is paragraph 2 related to paragraph 3?

In saying that ephemerals will develop “vigorously" when there is favorable precipitation, the author means that their development will be

The word “countering” in the passage is closest in meaning to

According to paragraph 4, some desert plants with root systems that are extraordinarily well developed have

The word “assured” in the passage is closest in meaning to

What do “the date palm, tamarisk, and mesquite" have in common?

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.

It can be inferred from paragraph 6 that all of the places desert animals retreat to

According to paragraph 7, what special adaptation helps the ostrich cope with hot desert conditions?

Look at the four squares  that indicate where the following sentence could be added to the passage. For this reason, the total amount of plant material in a desert is often 100 times less than the amount of plant material in an equivalent area of temperate forest.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: Select from the seven sentences below the three sentences that are true of Adaptations of Perennials and the two sentences that are true of Adaptations of Annuals. Drag each sentence you select into the appropriate column of the table. Two of the sentences will NOT be used. This question is worth 3 points.

Survival of Plants and Animals in Desert Conditions 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.