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Life in the Desert In the asutere and inhospitable environment of the desert, each inhabitant must be highly specialized in order to survive. In spite of the common notion that a desert is deserted of life, there are actually many living organisms. The pricipal limiting factor for successful animal and plant species is, obvious, the dearth of water, and some of the most-significant adaptations have evolved in solution to this basic problem. In the desert, many of the plants are annuals, lasting only one season. Some are ephemerals, lasting only a day. Many plants have reduced leaf surfaces, or they have transmuted them into sharp thorns. Some species, such as mosses and lichens, curl their leaves during the dry periods. Other plants have fleshy tissues in which they concentrate and conserve great quantities of reserve water. Still others plants grow only in the proximity of sources or basins of water dispersed in the desert(in oases) or around riverdeds where underground water flows. These plants have extremely long roots, which reach down to the moisture coming from the permanent water table. This is the case for the well-known date palm of the oases in the Sahara and the Middle East. When the water layer is too distant, however, other species live by spreading their roots along the surface in order to enjoy the moisture that condenses during the night but insufficient to penetrate deeply into the soil. Adaptation that are equally remarable can be seen among the animals, whcih, in order to survive; have no fewer problems to resolve than do the plants. Heat and lack of water are again principal factors limiting the possibility of life, the factors that must be addressed by the choices and strategies of each individual organism. To these factors is often added the scarcity of food, which is partically resolved by the low density of animals in the desert. Similarly to what happens during the winter of the temperate latitudes, when many species hibernate, desert animals reduce their metabolism during the summer by becoming less active, often in the shelter of rocks or underground. The same can occur in the case of prolonged drought. This reasonal behavior recalls what also happens on the scale of a single day, activities are stopped during the hottest hours, and everyone seeks shelter in the shade. Large-dimensioned species, such as hoofed or carnivorous mammals, which are endowed with relative facility of movement, as flying insects and birds are also, often undertake nomadic movements or actual migrations to find more-hospitable areas during period that are particularly unfavorable because of high temperature or drought. There are many adaptations in form and function to the torrid climate of the desert. For the purpose of more easily dispersing the heat, animals in hot desert region have smaller bodily dimensions than similar species living in colder areas. The opposite is true for the appendages, which are more developed and sometimes moist in animals living in hot areas, in order to cool off more easily. This is the case for the enormous ears of the jacrabbit--the hare of the Sonora Desert in America. Many desert animals are capable of tolerating long periods urine that is highly concentrated, thus reducing their loss of water. Some desert mice, alternatively, conserve the water that would be lost in respiration by maing it pass through a series of intricate ducts that open into the nasal sinuses, where the air loses moisture as it cools. So, are you satisfied with the above?? I feel tired~~~~ | 
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发表于 2008-4-28 14:47:00
楼主
，主要是我觉得口语的主观题和独立写作都是蛮无聊的问题，就好像前几次有一个题目是什么上11个月的课好不好，哎！ETS真是挖空心思啊，而且对于无聊问题还要用逻辑的方式阐述，自己写着也蛮想吐的
