久久亚洲国产成人影院-久久亚洲国产的中文-久久亚洲国产高清-久久亚洲国产精品-亚洲图片偷拍自拍-亚洲图色视频

您現在的位置: > Language Tips > Easy English > Odd Question  
 





  Why do leaves change color?
[ 2006-04-06 08:51 ]

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 green pigment 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 leaves disintegrates.

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 pigment carotene, the same pigment that gives carrots their bright orange color.

Red, wine-red, and purple leaves contain the pigments anthocyanins, which also lend their color to radishes, cabbage, roses, and geraniums. 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 thin veins that, 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 by tannins, 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.

 

note:

 

pigment: 色素
chlorophyll: 葉綠素

 

 

disintegrate: 分解

 

carotene: 胡蘿卜素

 

anthocyanins: 花青素
radish: 蘿卜
geraniums: 天竺葵

 

 

 

 

 

vein: 紋理

 

 


tannis: 單寧酸

 
 
 




主站蜘蛛池模板: 国产在线视频精品视频免费看 | 美美女高清毛片视频免费观看 | 交视频在线观看国产网站 | 欧美一级片在线免费观看 | 国产网红自拍 | gay毛片 | 免费a级毛片大学生免费观看 | 日韩视频在线观看中字 | 日本高清福利视频在线观看 | 国产午夜毛片一区二区三区 | 亚洲成年网 | 国产性生交xxxxx免费 | 亚洲在线成人 | 国自产精品手机在线视频香蕉 | 91综合精品网站久久 | 成人精品视频在线 | 久草在线观看视频 | 韩国一级毛片在线观看 | 男女牲高爱潮免费视频男女 | 日韩三级视频在线 | ccav在线永久免费看 | 欧美怡红院高清在线 | 一级毛片视频播放 | 亚洲香蕉影院 | 国产精品正在播放 | 日韩免费一级a毛片在线播放一级 | 中国国产一级毛片视频 | 91精品在线国产 | 欧美深夜影院 | 亚洲第一激情 | 亚洲精品国产成人专区 | 成年人国产 | 欧美一级毛片高清毛片 | 理论片我不卡在线观看 | 草草影院第一页yycccom | 国产精品1区2区3区 国产精品1区2区3区在线播放 | 成年美女黄网站色视频大全免费 | 日韩一级生活片 | 国产一区国产二区国产三区 | 手机免费在线看毛片 | 久草在线观看首页 |