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listen to part of a lecture in a botany class.
請聽植物學課上的部分內容。
It’s autumn and as you know in most parts of the United States, the leaves on the trees are changing color from green to yellow, orange and lots of other colors.
現在是秋天，正如你們所知，在美國的大部分地區，樹上的樹葉正從綠色變成黃色、橘色和很多其他顏色。
So this will be a great time to talk about how and why some of these leaves turn one color in particular and that’s bright red.
所以現在是個絕佳的時機來談論一些樹葉是如何以及為什么會變成一種特別的顏色，那就是亮紅色。
Well, before we discuss why leaves turn red,
在我們討論樹葉為什么會變紅之前，
first, let’s, um, look, I know this is very old material, but just to play it safe, let’s first go over why leaves are usually green.
我們首先......我知道這是非常老的材料，但是為了保險起見，我們先來過一遍樹葉為什么通常是綠色的。
It’s chlorophyll, right? Leaves get their green color from chlorophyll, the chemical that’s responsible for photosynthesis.
是葉綠素對吧？樹葉從葉綠素中獲得它們的綠色，這種化學物質是產生光合作用的原因。
The chlorophyll in the leaves collects energy from the Sun in the form of sunlight and it converts this energy into sugar which is food for the plants.
樹葉中的葉綠素從太陽的陽光中收集能量，然后將這種能量轉化成植物的食物——糖。
It’s chlorophyll that makes leaves green most of the time.
讓樹葉在大部分時候保持綠色的正是葉綠素。
Now, the classic explanation for why leaves change color is this: in autumn, the leaves start preparing for the winter and stop synthesizing new chlorophyll.
對樹葉為什么會變顏色的傳統解釋是：在秋天，樹葉開始為冬天做準備，停止合成新的葉綠素。
Since chlorophyll is sensitive to sunlight and to cold temperatures, both of which you get in autumn, the existing chlorophyll in the leaves breaks down.
因為葉綠素對陽光和低溫很敏感，而在秋天這兩個因素都有，所以樹葉中存在的葉綠素開始分解。
And since it’s not been replaced by the new chlorophyll, the green color of the leaves gradually fades away.
由于沒有新的葉綠素來代替它，樹葉的綠色漸漸消退。
As this happens, the other pigments present in the leaf become visible.
這種現象發生時，樹葉中的其他色彩開始顯現。
