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EXTRA4 The word "inhibit" in the passage is closest in meaning to

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What Controls Flowering
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The timing of flowering and seed production is precisely tuned to a plant's physiology and the rigors of its environment. In temperate climate plants lost flower early enough so that their seeds can mature before the deadly winds of autumn. Depending on how quickly the seed and food develop flowering may occur in spring as it does in oaks; in summer as in lettuces; or even in autumn as in asters.

What environmental cues do plants use to determine the seasons? Most cues such as temperature or water availability are quite variable: autumn can be warm; a late snow could fall in spring; also summer might be unusually cool and wet. So the only reliable cue is day length: longer days always mean that spring and summer are coming; shorter days foretell the onset of autumn and winter.

With respect to flowering botanists classify plants as day neutral, long day or short day. A day neutral plant flowers as soon as it has sufficiently grown and developed regardless of the length of day. The neutral plants include tomatoes, corn, snapdragons and roses. Although the naming is traditional, long day and short day plants are better described as short night and long night plants because their flowering actually depends on the duration of continuous darkness rather than on day length. Short night plants (which include lettuces, spinach, iris, clover and petunias) flower when the length of darkness is shorter than a species' specific critical period. Long night plants(including asters, potatoes, soy beans, goldenrod and cockleburs) flower when the length of uninterrupted darkness is longer than the species' specific critical period. Thus spinach is classified as a short night plant because it flowers only if the night is shorter than eleven hours (its critical period), and the cocklebur is a long night plant because it flowers only if an uninterrupted darkness lasts more than 8.5 hours. Both of these plants will flower with ten-hour nights.

Plant scientists can induce flowering. Plant scientists can induce flowering in the cocklebur by exposing leaves to long nights (longer than its 8.5 hour critical period) in a special chamber, while the rest of the plant continues to experience short nights. Clearly, a signal that induces flowering transmitted from the leave to the flowering bud. Plant physiologists have been attempting for decades to isolate these elusive signaling molecule often called florigen (literally, flowering maker). Some researchers believe they are close to demonstrating a flower's stimulating substance for specific type of plant. Using genetic manipulation, it is likely, however, that interactions among multiple and yet unidentified planthormones stimulate or inhibit flowering, and that these chemicals may differ among plant species. Researchers have had more success in determining how plants measure the length of uninterrupted darkness, which is a crucial stimulus for producing whatever substance control flowering.

To measure continuous darkness, a plant needs two things: some sort of metabolic clock to measure time (the duration of darkness) and a light detecting system to set the clock. Virtually all organisms have an internal biological clock that measures the time even without environmental cues. In most organisms including plants, the biological clock is poorly understood, but we know that the environmental cues, particularly light, can reset the clock. How do plants detect light? The light detecting system of plants is a pigment in leaves called phytochrome (literally, plant color).

Plants seem to use the phytochrome system in combination with their internal biological clocks to detect the duration of continuous darkness. Cockleburs, for example, flower under the schedule of sixteen hours of darkness and eight hours of light. However, interrupting the middle of the dark period with just a minute or two of lights prevents flowering. Thus their flowering is controlled by the length of continuous darkness. It is evident that even brief exposure to sunlight or white light will reset their biological clocks. The color of the light used for the light exposure is also important. A nighttime flash of pure red light inhibits flowering, while flash of light at the far-red end of the spectrum has no effect on flowering, as if no light were detected.

10.The word "inhibit" in the passage is closest in meaning to

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本题为词汇题。“inhibit”的意思是“抑制;禁止”,词汇所在句“Using genetic manipulation, it is likely, however, that interactions among multiple and yet unidentified plant hormones stimulate or inhibit flowering”在文中的意思是“利用基因操作,这是有可能实现的。然而,多个尚未确认的植物激素之间的相互作用刺激或抑制开花。”如果大家不认识inhibit这个单词,一些解题技巧也能帮助我们解题。首先or链接了stimulate和inhibit两个单词,or表示选择,所以我们猜测stimulate和inhibit应该是反义词。如果是近义词的话,连接词应该是and。而stimulate的意思是“刺激;激励”所以inhibit应该有“抑制”的意思。此外,“in-”这个词根代表“不,无,非”,具有消极意义,词根也可以帮助我们猜出答案。 A选项speed up的意思是“加速,加快”,排除。 B选项restrain的意思是“制止;抑制”,意思与inhibit相近,故为正确答案。 C选项contribute的意思是“贡献出”,排除。 D选项prolong的意思是“延长,拉长”,排除。

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