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【判断题】
大白菜接近地面的烂掉了，流出黑水是由于真菌引发的病害A.
正确
B.
错误
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举一反三
【判断题】During the 20th century, the automobile rapidly developed from an expensive toy for the rich into a practical vehicle for transport in most developed countries. In developing countries, the practical ...
A.
正确
B.
错误
【单选题】一般而言,采用产品差异化战略的企业,具有以下特征( )。
A.
销售毛利率高，总资产周转率高
B.
销售毛利率高，总资产周转率低
C.
销售毛利率低，总资产周转率高
D.
销售毛利率低，总资产周转率低
【多选题】How does conformational changes in a transporter mediate the passive transport of a solute such as glucose?
A.
An important example of a transporter that mediates passive transport is the glucose transporter in the plasma membrane of many mammalian cell types. The protein, which consists of a polypeptide chain that crosses the membrane at least 12 times, can adopt several conformations—and it switches reversibly and randomly between them. In one conformation, the transporter exposes binding sites for glucose to the exterior of the cell; in another, it exposes the sites to the cell interior.
B.
Because glucose is uncharged, the electrical component of its electrochemical gradient is zero. Thus the direction in which it is transported is determined by its concentration gradient alone. When glucose is plentiful outside cells, as it is after a meal, the sugar binds to the transporter’s externally displayed binding sites; if the protein then switches conformation—spontaneously and at random—it will carry the bound sugar inward and release it into the cytosol, where the glucose concentration is low.
C.
Conversely, when blood glucose levels are low—as they are when you are hungry—the hormone glucagon stimulates liver cells to produce large amounts of glucose by the breakdown of glycogen. As a result, the glucose concentration is higher inside liver cells than outside. This glucose can bind to the internally displayed binding sites on the transporter. When the protein then switches conformation in the opposite direction—again spontaneously and randomly—the glucose will be transported out of the cells and made available for import by other, energy-requiring cells.
D.
The net flow of glucose can thus go either way, according to the direction of the glucose concentration gradient across the plasma membrane: inward if more glucose is binding to the transporter’s externally displayed sites, and outward if the opposite is true. Although passive transporters themselves play no part in controlling the direction of solute transport, they are highly selective in terms of which solutes they will move. For example, the binding sites in the glucose transporter bind only D-glucose and not its mirror image L-glucose, which the cell cannot use as an energy source.
【简答题】化简 sin(nπ+α)cos(nπ-α) cos[(n+1)π-α] ，n∈Z．
【单选题】The key advantages of _____ transport include relative speed, good availability, flexibility, and prompt adaptability to any changes in demands.
A.
rail
B.
road
C.
parcel
D.
air
【简答题】The European Union picked up the theme, and referred to it as Road Transport Informatics. In the course of time the name of this technology was subjected to many changes 6) __________ the USA gave it...
【简答题】Concorde SST The most impressive aircraft f the jet age was the supersonic transport aircraft, Concorde. This aircraft flew faster than the speed of sound and allowed three hour flights between New Yo...
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