Why leaves change color(10.12)课件.ppt

Why leaves change color 争替圃恋嘛猪熔勿缴酵示虐弹生疥滓韵退哆扛讨瞄虎吨表婚左壁勒惹晕俞Why leaves change color(10.12)课件Why leaves change color(10.12)课件 You dont need a vivid imagination to picture Mother Nature, on autumn days with a liberal supply of paint, beautifully coloring the leaves of the trees and other plants. Every year at this time, we are awed by the beauty of the trees, knowing it is only temporary. Before long the leaves will fall and become a part of the rich carpet that covers the forest floor. Many people suppose that Jack Frost causes this color change, but he doesnt. Some of the leaves begin to turn before we have any frosts. Native Americans thought it was because the celestial hunters had slain the Great Bear – his blood dripping on the forests changing the leaves of many trees to red. Other trees were turned yellow by the fat that splattered out of the kettle as the hunters cooked meat for supper. 入秋时分，大自然缤纷的色彩绚丽地点缀着树叶和其他的植物。你无需丰富的想象力就可以描画出大自然母亲。每年的这个时候，树木的美丽短暂而令人惊叹，然后落叶纷纷覆盖森林犹如华丽的地毯。人们以为是严霜令树叶变色，但其实不然。有些树叶在霜冻来临之前就已经开始变色了。美洲原住民认为是由于天上的猎人杀死了大熊星座的大熊，鲜血滴落森林使得许多树叶变成了红色。而其他变成黄色的树叶则是由猎人大锅烹熊煮肉做晚餐时溅出来的肥油染黄的。 然后纷纷落叶将融入森林如地毯般丰腴的土地 落叶飘零，滋养大地。 讶荧咏肃博为戌荧爪匝亩掐卢辟颤椒遂镇处随蒂条辐限讼礼泼汾阴疏憨颧Why leaves change color(10.12)课件Why leaves change color(10.12)课件 We now know that change in coloring is the result of chemical processes that take place in the tree during its preparation for winter. In spring and summer, the leaves serve as factories where foods for the trees growth are manufactured. This food-making takes place in millions of tiny cells in the leaf and is carried on by small green bodies, called chlorophyll, that give the leaf its color. These chlorophyll bodies make food for the tree by combining carbon from the air with hydrogen, oxygen, and various minerals in the water the roots gather. In the fall, cool weather causes a slowing down of vital processes, and the work of the leaves ends. The machinery of the leaf factory is dismantled, so to speak. The green chlorophyll is broken up into the va