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
23
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] Which of the following has nothing to do with chlorophyll?
选项
A、The nutrients-producing process of the trees.
B、Leaves which turn green in the spring.
C、Grass which becomes yellow in the spring.
D、Young leaves that are red in the spring.
答案
D
解析
末段首句和末句表明红色并非来自叶绿素,末句中的buds与选项D中的young leaves同义,由此可见,选项D为正确的说法。
转载请注明原文地址:https://tihaiku.com/zcyy/3528958.html
相关试题推荐
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
随机试题
Duringastateofdeeprelaxation,severalphysiologicalchangestakeplace
[originaltext]M:Honey,thebasketballgameisabouttostart.Andcouldyoubr
Whatwastrueofthedemonstrators?[br][originaltext][28C]Some150Sout
Inmultipointnetworks,therearetree
A.妊娠18~20周 B.妊娠5周 C.妊娠20~24周 D.妊娠12周
包价旅游合同应当采用书面形式,旅行社未与旅游者订立书面合同的,旅游行政主管部门可
胃黏膜中哪种细胞产生与维生素B12吸收有关的内因子?A、G细胞 B、壁细胞
治疗药物浓度监测的标本采集时间一般选择在A.任一次用药后1个半寿期时B.药物消除
下列地区的气候属于热带季风气候的有:A.中南半岛 B.雷州半岛 C.阿拉伯半
下列筹资方式中,一般属于间接筹资方式的有( )。A.优先股筹资 B.融资
最新回复
(
0
)