首页
登录
职称英语
It is a common belief that sharp frosts color the autumn leaves. As a matter
It is a common belief that sharp frosts color the autumn leaves. As a matter
游客
2024-03-12
68
管理
问题
It is a common belief that sharp frosts color the autumn leaves. As a matter of fact, such frosts are far more likely to turn leaves black or dull brown than to give them the gorgeous tints we admire.
The coloring of the leaves in the fall is a chemical process that is favored by gradual cooling rather than sudden cold. It is not entirely confined to the autumn. Bright red and yellow leaves are often found on the swamp maple and other trees, even in summer.
Through the season of growth the leaves serve as food factories for the trees. In their tiny cells the carbon of the air is combined with materials brought up by the tree fluid from the roots to form the starch, sugar, and other substances by which the whole tree is fed. The food-making process is performed by sunshine with the aid of a substance called chlorophyll. Chlorophyll is a mixture of several pigments, or coloring matters. One of these is green, and gives the leaves their ordinary color. Another is yellow and is the same substance that, on account of its abundance in growing grass, makes butter particularly yellow in the spring.
When the cool weather sets in and the growth of vegetation slows down, the trees need less food and gradually suspend work in the leaf factories. Both the food and the chlorophyll in the leaves are drawn into the body of the tree and stored up for use in the spring. This transfer involves many chemical changes. One of them is the breaking up of the chlorophyll into the substances of which it is composed. The green pigment passes out of the leaves before the yellow. Thus yellow becomes one of the prevailing hues of the autumn foliage.
The reds, which also prevail in the autumn, do not come from the chlorophyll, but from pigments contained in the sap. Their appearance indicates an excess of sugar in the leaves, after the withdrawal of other materials. It is supposed, also, that the reddening of the leaves protects the food materials from the harmful effects of strong light during their passage into the tree. The same red coloring is seen in the buds of many plants in the spring, where it probably also serves a protective purpose. [br] The amount of sunlight may most probably influence ______.
选项
A、the timing when the leaves change colors
B、the quality of the nutrients for the trees
C、the speed of the food-making process
D、the variety of pigments in the chlorophyll
答案
B
解析
原文末段第3句暗示强烈的阳光会破坏食物的品质,由此可见,阳光对供给植物的营养物会产生影响,即选项B的说法。
转载请注明原文地址:https://tihaiku.com/zcyy/3528954.html
相关试题推荐
______(不管中国变得多么强大),itwillconstitutenothreattoanyothercountry.Nomatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
随机试题
It’stemptingtospendslowworkdaysthisholidayseasonshoppingforgifts
[originaltext](10)ThePhilippinegovernmentbasbannednewsreportsabout
Iwouldhavegonetothelecturewithyou______Iwassobusy.A、exceptthatB、pr
Here’sawarningfromhealthexperts:Sittingisdeadly.Scientistsareinc
()滤波器在对图像复原过程中需要计算噪声功率谱和图像功率谱。A.逆滤波 B.维
在建筑产品的生产、维修、拆除过程中,操作人员违反有关施工操作规程等而直接导致的安
抗毒素:()A.为外毒素经甲醛处理后获得 B.可中和游离外毒素的毒性作
①谣言止于智者,粉碎谣言靠的还是民众自身的审慎与理性 ②流通的信息不仅要多,更
在计算所得税的各项扣除时,企业发生的公益性捐赠支出,在年度利润总额( )以内的部
压力试验过程中如发现泄漏、异常响声等不正常情况,应停止试验并( ),经修补处理
最新回复
(
0
)