91小视频在线观看-91小视频在线观看-91小视频-91小视频-欧美成人免费视频-欧美成人免费电影

食品伙伴網服務號
 
 
當前位置: 首頁 » 專業英語 » 資源技巧 » 正文

樹葉為什么會變色

放大字體  縮小字體 發布日期:2008-03-06
核心提示:銀杏樹葉黃了,楓葉紅了秋天的樹木都換上了新裝。在欣賞自然美景的同時,我要問大家一個問題:你知道樹葉為什么會變色嗎? Leaves change color in the fall, because the chemical changes in the leaves, as their nutrients drain into the tree's branches, trunk,


    銀杏樹葉黃了,楓葉紅了……秋天的樹木都換上了新裝。在欣賞自然美景的同時,我要問大家一個問題:你知道樹葉為什么會變色嗎?

    Leaves change color in the fall, because the chemical changes in the leaves, as their nutrients drain into the tree's branches, trunk, and roots for winter storage, cause the leaves to stop producing the greenpigment chlorophyll.

    Chlorophyll's role in the leaves, to absorb sunlight and to use the sun's energy, is no longer necessary, and the remaining chlorophyll in the leavesdisintegrates.

    When the pigment chlorophyll departs, secondary pigments, substances that also absorb light, emerge to take its place, and change the leaves' colors to theirs. For example, yellow and orange leaves contain the pigmentcarotene, the same pigment that gives carrots their bright orange color.
Red, wine-red, and purple leaves contain the pigmentsanthocyanins, which also lend their color toradishes, cabbage, roses, andgeraniums. The main difference between carotene and anthrocyanins is that the anthrocyanins only form in the leaves in the fall when the weather becomes cooler, especially when the temperature falls to between 32 degrees to 45 degrees Fahrenheit.

    One characteristic of the leaves' color is that, for the most part, it is inherited. The variations in the color, however, are determined by weather conditions. The richest and most brilliant foliage appears after weeks of cool, sunny weather in places in the United States such as New England.
The color of the leaves fade as fall turns to winter, and the stems that secure them to the branches begin to loosen with the change in weather. The cells at the ends of the stems fall apart, leaving the leaves attached to the branches by the thinveinsthat, in warmer weather, transported water and nutrients to the leaves. At this point, virtually any movement can break the veins and the leaves tumble to the ground.

    Although the yellow and red pigments last for a few days once on the ground, they soon disintegrate just as the green chlorophyll pigment did. All that remains are brown leaves colored bytannins, which also give tea its brown color. Without a water supply, the brown leaves carpeting the ground become dry and brittle, and the trees bare

 

更多翻譯詳細信息請點擊:http://www.trans1.cn
 
關鍵詞: 樹葉 變色
[ 網刊訂閱 ]  [ 專業英語搜索 ]  [ ]  [ 告訴好友 ]  [ 打印本文 ]  [ 關閉窗口 ] [ 返回頂部 ]
分享:

 

 
推薦圖文
推薦專業英語
點擊排行
 
 
Processed in 0.169 second(s), 17 queries, Memory 0.9 M
主站蜘蛛池模板: 麒麟色欧美影院在线播放 | 高清毛片aaaaaaaaa片 | 亚洲天天做日日做天天欢毛片 | 美女视频一区二区三区 | 色中色资源 | 伊人网在线免费视频 | 欧美一级日韩在线观看 | 99国产国人青青视频在线观看 | 国产免费卡1卡2卡 | 狠狠色狠狠色综合网 | 日本成人免费在线视频 | 正在播放91 | 久久国产香蕉视频 | 日日摸夜夜爽 | 瑟瑟久久 | 国产三级日产三级韩国三级 | 亚洲免费在线观看 | 成年人看的毛片 | 美女扒开尿口给男人桶视频免费 | 精品成人毛片一区二区视 | 性欧美高清久久久久久久 | 狠狠色依依成人婷婷九月 | 天天操欧美 | 在线观看免费视频国产 | videosex久久麻豆 | 免费观看片| 五月婷婷在线播放 | 深爱五月婷婷 | 特黄特色大片免费视频播放 | 99草在线观看 | 淫欲网 | avtom影院永久地址人人影院 | 三级在线免费 | 午夜三级成人三级 | 妇少香港三日本三级视频 | 黄色录像大全 | 手机看片免费永久在线观看 | 2022天天操| 四虎永久免费最新在线 | 日本免费网| 酒色网址 |