题目内容
细菌在血中大量繁殖是（）。
查看答案
搜索结果不匹配？点我反馈
更多问题
Koalas, an Australian tree-climbing animal, are very particular about what they eat, devoting themselves entirely to a diet of the leaves of eucalyptus trees. But there are problems associated with an exclusive diet of leaves, especially if, like the koala, you happen to be a relatively small animal. One of these problems is that the leaves of trees are rich in fibre, and so resist digestion. Eucalyptus leaves are worse than most, for they contain large amounts of lignin, the indigestible, woody material found in the cell walls of many plants. But there is another drawback for the koala. The ratio of an animal’s gut volume to its energy requirements depends on body mass; the smaller it is, the lower the ratio. So tiny leaf-eaters are likely to have difficulty processing sufficient quantities of their poor-quality food to meet their metabolic needs. S. J. Cork and T. J. Dawson of the University of New South Wales and I. D. Hume of the University of New England have made a study of the koala’s digestion. They have identified three major factors that allow koalas to exploit its fibre-laden diet. In the first place, the koala has a discerning digestive system; like the rabbit, it can regulate the passage of food through its gut in a way that discriminates between particles of different sizes. The alimentary canal retains and solutes smaller, more digestible particles, while expelling unwanted, coarser matter. This is probably a space-saving exercise; it has the effect of increasing the rate at which raw material can be fed into the system. The second factor behind the koala’s success is that it has a low overall requirement for metabolic energy, compared to other Australian animals of similar size. So it saves on its fuel needs. In this respect, the koala is not dissimilar to another slow-moving, leaf eating mammal, the three-toed sloth. Thirdly, eucalyptus leaves have hidden qualities. Despite the large quantity of lignin, such leaves are rich in digestible energy -especially in the form of fatty substances. Not all such resources are available to the koala’s metabolic machinery; essential oils are passed out, for example. But some fatty substances are available, as are sugar and starch. It is these compounds that satisfy the bulk of the koala’s energy needs. Surprisingly, constituents of the eucalyptus’s cell walls, such as cellulose, are less important. Some cellulose is digested, but the koala’s accomplishments in this field do not rival those of other animals that reshow. The purpose of Cork, Dawson and Hume study is to
钠石灰中含（）
A new variety of sugar cane, bred from crosses of ordinary cultivated strains with a wild type found in Argentina, could become an important source of energy as well as sugar. Two conditions need to be fulfilled to make it worthwhile to cultivate an agricultural crop for energy. The crop must be easy to harvest and process, and it must be high-yielding. On both these counts, sugar cane is ideal: the technology for harvesting and milling has been thoroughly tested over the years, and sugar cane is one of the most productive plants ever recorded. Professor Mike Giamalva and his colleagues at Louisiana State University have now produced a plant that is super-productive. Their new variety grows to 3.6 metres high. On experimental plots, it gives yields of 253 tons per hectare -equal to the highest yield of any plant recorded. But even this record has been exceeded. On good soil, yields may reach 321 tons per hectare. Another advantage of Giamalva’s new strain of sugar cane is its high fibre content. Traditionally, researchers have selected strains that produce large amounts of juice rich in sugar, and low quantities of fibre. The fibre is either discarded, or sometimes burnt as fuel. The new sugar cane gives exceptional quantities of fibre for only modest amounts of juice. When it comes from the mill, the bagasse has about 70 per cent of the heat content of wood, or 30-40 per cent of that of coal. Burning bagasse to provide energy is not a new idea. Many sugar factories throughout the world are now self-sufficient in energy, while some, for example, in Mauritius, Hawaii and South Africa, "export" electricity to the national grid. Mauritius currently gets around 10 per cent of its electricity from sugar factories. However, in Louisiana local farmers are unwilling to grow the cane until they have a guaranteed market. Yet industrialists will not invest in the new fuel until they have a constant supply. And only local factories may be able to exploit cane because, being bulky, it is costly to transport. One way of overcoming this problem would be to dry the fibrous residue and compact it. Work on compacting fibrous residue is now under way in several research centres. Whether compacting will pay its way will depend on the local situation and the cost of alternative energy supplies. A study carried out by Fay Baguant from the University of Mauritius showed that electricity could be produced there from fibrous residue about twice as cheaply as from oil or coalfired stations. The new variety can be grown with ordinary sugar cane or with other crops to provide energy for processing. It can be compressed and burned as a substitute for charcoal. Or it can be incorporated into paper, cardboard and fibreboard. Brazil, with its fleet of cars running almost entirely on alcohol fuel extracted from sugar cane, already has shown that the plant has the potential to alter radically a country’s agricultural sector. What is special of Mike Giamalva’s new sugar cane
A new variety of sugar cane, bred from crosses of ordinary cultivated strains with a wild type found in Argentina, could become an important source of energy as well as sugar. Two conditions need to be fulfilled to make it worthwhile to cultivate an agricultural crop for energy. The crop must be easy to harvest and process, and it must be high-yielding. On both these counts, sugar cane is ideal: the technology for harvesting and milling has been thoroughly tested over the years, and sugar cane is one of the most productive plants ever recorded. Professor Mike Giamalva and his colleagues at Louisiana State University have now produced a plant that is super-productive. Their new variety grows to 3.6 metres high. On experimental plots, it gives yields of 253 tons per hectare -equal to the highest yield of any plant recorded. But even this record has been exceeded. On good soil, yields may reach 321 tons per hectare. Another advantage of Giamalva’s new strain of sugar cane is its high fibre content. Traditionally, researchers have selected strains that produce large amounts of juice rich in sugar, and low quantities of fibre. The fibre is either discarded, or sometimes burnt as fuel. The new sugar cane gives exceptional quantities of fibre for only modest amounts of juice. When it comes from the mill, the bagasse has about 70 per cent of the heat content of wood, or 30-40 per cent of that of coal. Burning bagasse to provide energy is not a new idea. Many sugar factories throughout the world are now self-sufficient in energy, while some, for example, in Mauritius, Hawaii and South Africa, "export" electricity to the national grid. Mauritius currently gets around 10 per cent of its electricity from sugar factories. However, in Louisiana local farmers are unwilling to grow the cane until they have a guaranteed market. Yet industrialists will not invest in the new fuel until they have a constant supply. And only local factories may be able to exploit cane because, being bulky, it is costly to transport. One way of overcoming this problem would be to dry the fibrous residue and compact it. Work on compacting fibrous residue is now under way in several research centres. Whether compacting will pay its way will depend on the local situation and the cost of alternative energy supplies. A study carried out by Fay Baguant from the University of Mauritius showed that electricity could be produced there from fibrous residue about twice as cheaply as from oil or coalfired stations. The new variety can be grown with ordinary sugar cane or with other crops to provide energy for processing. It can be compressed and burned as a substitute for charcoal. Or it can be incorporated into paper, cardboard and fibreboard. Brazil, with its fleet of cars running almost entirely on alcohol fuel extracted from sugar cane, already has shown that the plant has the potential to alter radically a country’s agricultural sector. The writer’s attitude towards the potentials of the new sugar cane is
微信支付 
支付宝支付