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  3. WHAT CONTROLS FLOWERING (1) The timi

WHAT CONTROLS FLOWERING (1) The timi

游客2024-01-02  56
问题                                         WHAT CONTROLS FLOWERING
    (1) The timing of flowering and seed production is precisely tuned to a plant’s physiology and the rigors of its environment. In temperate climates, plants lost flowers early enough so that their seeds can mature before the deadly winds of fall. Depending on how quickly the seeds and food develop, flowering may occur in spring as it does in oaks; in summer as in lettuces; or even in fall as in asters.
    (2) What environmental cues do plants use to determine the seasons? Most cues such as temperature or water availability are quite variable: Fall 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 fall and winter.
    (3) 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, irises, clover and petunias) flower when the length of darkness is shorter than a species’ specific critical dark period. Long-night plants (including asters, potatoes, soybeans, goldenrod, and cockleburs) flower when the length of uninterrupted darkness is longer than the species’ specific critical dark period. Thus spinach is classified as a short-night plant because it flowers only if the night is shorter than 1I hours (its critical dark 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 10-hour nights.
    (4) Plant scientists can induce flowering in the cocklebur by exposing leaves to long nights (longer than its 8.5-hour critical dark 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 molecules 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 plant hormones 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 controls flowering.
    (5) 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).
    (6) 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 16 hours of darkness and 8 hours of light. However, interrupting the middle of the dark period with just a minute or two of light prevents flowering. [A] Thus their flowering is controlled by the length of continuous darkness. [B] It is evident that even brief exposure to sunlight or white light will reset their biological clocks. [C] The color of the light used for the light exposure is also important. A nighttime flash of pure red light inhibits flowering, while a flash of light at the far-red end of the spectrum has no effect on flowering, as if no light were detected. [D] [br] 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. |
选项 A、Traditionally, long-day and short-day plants are better known as short-night and long-night plants because they actually flower during periods of continuous darkness.
B、The naming of long-day and short-day plants is traditional and depends on whether they flower during long days or long nights.
C、Whether plant is better described in terms of day length or night depends on whether it flowers during the day or during continuous darkness.
D、Despite their traditional names, the flowering of what are called long-day and short-day plants actually depends on the length of continuous darkness rather than on day length.
答案 D
解析 本题考查对文中高亮句子的理解和同义转述，属于句子简化题。解题关键在于对句子中的原因状语从句的理解。原文句子提到，尽管根据传统习惯．“它们”被命名为长日照和短日照植物，但由于其开花实际上取决于黑暗的持续时间，而非日照时间的长短(their flowering…depends on the duration of continuous darkness rather than on day length)，所以把它们称为短夜植物和长夜植物会更好。D项转述了该句的主要信息，其中，介词Despite后接的状语与原文Although引导的状语从句意思相同，而该项的主干内容则是原文原因状语从句的同义表述(the length of是原文the duration of的同义替换)。A项“从传统意义而言，长日照植物和短日照植物被称为短夜植物和长夜植物更好，因为它们实际上在持续黑夜的状态下开花”、B项“长日照植物和短日照植物的叫法是传统的，且取决于它们是否在长日或长夜里开花”和C项“以日长还是夜长来描述植物更好，取决于植物是在白天开花还是在持续黑暗里开花”均是对原文事实信息在某种程度上的扭曲。
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