首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
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 le
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 le
admin
2020-04-14
45
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.
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://kaotiyun.com/show/f4W7777K
0
大学英语六级
相关试题推荐
Everyyearthroughouttheworld【C1】______6,000earthquakesaredetected.Thevastmajorityoftheseare【C2】______toosmallorto
ContrarytocommonbeliefsocialmediawebsitessuchasFacebookdonot【C1】______personalties,theystrengthentheminuniquew
ContrarytocommonbeliefsocialmediawebsitessuchasFacebookdonot【C1】______personalties,theystrengthentheminuniquew
ContrarytocommonbeliefsocialmediawebsitessuchasFacebookdonot【C1】______personalties,theystrengthentheminuniquew
I’vealwaysbeenanoptimistandIsupposethatisrootedinmybeliefthatthepowerofcreativityandintelligencecanmaketh
I’vealwaysbeenanoptimistandIsupposethatisrootedinmybeliefthatthepowerofcreativityandintelligencecanmaketh
A、They’resimilartoaradio-controlledmodelaircraft.B、Theyflythroughouttheworldfreelyjustlikeeagles.C、Theycanauto
Throughouthistorymanhasobservedsuchnaturalcyclesastherisingandsettingofthesun,theebbandflowoftheoceantide
Throughouthistorymanhasobservedsuchnaturalcyclesastherisingandsettingofthesun,theebbandflowoftheoceantide
随机试题
无机结合料稳定基层施工对原材料的技术要求,包括()。
根据《公路工程质量监督规定》的规定,建设单位对未经工程质量检测或者质量检测不合格的工程,按照合格工程组织交工验收的,责令改正,处工程合同价款()以下的罚款。
充分授权制度要求:商业银行应妥善保管合同和授权文件,并且至少每年确认()。
关于完全垄断企业的需求曲线和收益曲线的说法,正确的是()。
将如下所示图形折叠起来后,应该是四个选项中的()。
背景说明:你是宏远公司的总经理助理施林,下面是总经理需要你完成的几项工作任务。便条施林:根据工作计划,下月我将出访德国××公司,由你随行。请你以书面方式向我介绍一下
南方某航空专科学校指令学校杨某、陈某负责制定郑和宝船模型图,并雇请木器厂工人晨某照图制成郑和宝船航模。同年,学校确定杨某、陈某组织撰写有关郑和宝船模型的论文。杨、陈随即各自着手整理资料,陈某将自己执笔写成的两篇论文初稿,均署名陈、杨二人,送杨某定稿,杨某只
2009年国务院政府工作报告中指出,在市场化需求增长乏力的背景下,“大幅度(),这是扩大内需最主动、最直接、最有效的措施。”
并蒂莲:鸳鸯
Collisionbetweenanaircraftandoneormorebirdsistermedabird-strike.Pilotssometimesrecordabirdstrikewhileatcruis
最新回复
(
0
)