Summer green夏天的綠
Look for the yellow dots behind the green ones. How many can you find?
在綠點後面找找黃點。你找得到幾個？
Living Things · Unit 2 · Lesson 8 · 生命與生態 單元二 第八課
Why Do Leaves Change Color?葉子為什麼會變色？
A leaf does not turn yellow in autumn. It was yellow all summer, and you could not see it. In a 3D model, look inside a leaf at the three pigments that color it. Move the season forward and watch the green fade until the yellow underneath shows through. Then choose a tree that turns red, and find out what kind of weather makes the brightest reds. Last, mix the three pigments yourself.
葉子不是到了秋天才變黃的。它整個夏天都是黃的，只是你看不見。在 3D 模型裡，看看讓葉子有顏色的三種色素。把季節往前推，看綠色慢慢褪去，底下的黃色露出來。接著選一棵會變紅的樹，找出什麼樣的天氣能讓紅色最鮮豔。最後自己動手調一調這三種色素。
Big idea · 一句話看懂
A green leaf holds more than one color. The green pigment, chlorophyll, is so strong that it hides the yellow and orange pigments that are there with it. In autumn the days grow short and cool. The tree stops renewing its chlorophyll and takes the useful parts back into its branches. As the green fades, the yellow and orange show. Some trees also make a red pigment at this time. Then the tree seals off each leaf, and the leaf falls.
一片綠色的葉子裡，其實不只一種顏色。綠色的色素——葉綠素——太強了，把同時存在的黃色和橘色色素都蓋住了。到了秋天，白天變短、天氣變涼，樹不再補充葉綠素，並且把裡面有用的東西收回枝條裡。綠色一褪，黃色和橘色就露出來。有些樹在這個時候還會另外製造一種紅色的色素。接著樹把每一片葉子的出入口封住，葉子就掉落了。
3D Model · 3D 模型
What Is Hiding in a Leaf 葉子裡藏著什麼
Drag to turn the model, and scroll or pinch to zoom. On the left is a leaf. The circle on the right is a closer look at the pigments inside it. Press Pause, and move the Season slider slowly from summer to autumn. Watch the green dots, and look at what was behind them the whole time. Then switch between the two kinds of tree, and turn Bright days, cool nights off and on.
拖曳可以旋轉模型，滾輪或雙指可以縮放。左邊是一片葉子，右邊的圓圈是把葉子裡的色素放大來看。按「暫停」，把「季節」滑桿從夏天慢慢拉到秋天。盯著那些綠點，再看看它們後面一直藏著什麼。接著在兩種樹之間切換，並把「白天晴朗、夜裡涼」關掉再打開。
Drag to turn · 拖曳旋轉 Scroll or pinch to zoom · 滾輪／雙指縮放
This 3D model needs WebGL, which this browser does not support. The reading and the cards below still explain everything.
這個瀏覽器不支援 WebGL，無法顯示 3D 模型；下方的課文與卡片一樣能看懂。
- Green dots: chlorophyll
綠點：葉綠素 - Yellow dots: carotenoids, there all year
黃點：類胡蘿蔔素，整年都在 - Red dots: anthocyanins, made in autumn by some trees
紅點：花青素，有些樹秋天才製造 - Brown: the cork layer at the base of the stalk
咖啡色：葉柄基部的木栓層
A teaching model. Pigments are molecules, far too small to see as dots, and they are spread all through the cells of the leaf. The amounts on the three bars and the color of the leaf are examples that follow the general pattern. Real trees differ from kind to kind and from year to year. The season slider covers several months.
這是教學用的模型。色素是分子，小到不可能看成一顆一顆的點，而且它們散佈在葉子的細胞裡。三條量表上的數量和葉子的顏色都是示意，只照著大致的規律走；真的樹，每一種、每一年都不一樣。季節滑桿涵蓋的是好幾個月。
Model drawn by My Culture Connect as a teaching diagram. The ideas follow the sources listed at the bottom of this page. · 模型由人師教育協會自繪示意；原理依本頁最下方列出的出處。
Reading · 英文閱讀
8
Unit 8: Why Do Leaves Change Color?
In some parts of the world, whole hillsides turn yellow, orange, and red for a few weeks every autumn. It looks as if someone has painted the trees. But most of that color was not added in autumn. It was in the leaves all summer.
世界上有些地方，每年秋天整片山坡會有幾個星期變成黃色、橘色和紅色，看起來就像有人替樹上了顏料。可是這些顏色大部分並不是秋天才加上去的，它們整個夏天都在葉子裡。
A leaf is green because it is full of chlorophyll. This is the pigment that catches sunlight so that the leaf can make food. There are other pigments in the leaf as well, yellow and orange ones called carotenoids. In summer you cannot see them, because there is so much green on top.
葉子是綠的，因為裡面充滿了葉綠素。這種色素負責捕捉陽光，讓葉子能夠做食物。葉子裡還有別的色素：黃色和橘色的，叫做類胡蘿蔔素。夏天你看不到它們，因為蓋在上面的綠色實在太多了。
Chlorophyll does not last. Sunlight wears it out, and the tree has to keep making more. In autumn the days grow shorter and cooler, and the tree stops. It breaks the chlorophyll down and moves the useful parts back into its branches, to keep through the winter.
葉綠素並不耐用。陽光會讓它耗損，樹得不停地補充。到了秋天，白天變短、天氣變涼，樹就不再補了。它把葉綠素拆開，把有用的部分搬回枝條裡，留著過冬。
As the green fades, the yellow and orange are still there, and now you can see them. That is all it takes to turn a tree gold.
綠色褪去以後，黃色和橘色還在，這時候你就看得到它們了。一棵樹變成金黃色，就只是這樣而已。
Red is different. Red comes from a third kind of pigment, and it is not in the leaf during the summer. Some trees make it in autumn from the sugar in their leaves. They make the most when the days are bright and the nights are cool but not freezing. That is why the same tree can be brilliant one year and dull the next.
紅色就不一樣了。紅色來自第三種色素，夏天的葉子裡並沒有它。有些樹到了秋天，才用葉子裡的糖把它做出來。白天晴朗、夜裡涼而不結霜的時候，做得最多。所以同一棵樹，可能今年紅得發亮，明年卻很黯淡。
At last the tree grows a thin layer of cork across the base of each leaf stalk. This shuts off the water. The leaf dries, turns brown, and falls. The tree has not lost much. It has taken back what it could, and it will grow new leaves in spring.
最後，樹在每一根葉柄的基部長出一層薄薄的木栓，把水路關上。葉子乾掉、變成褐色，然後掉落。樹並沒有損失多少：能收回的都收回了，春天會再長出新的葉子。
Read aloud · 課文朗讀
Questions · 閱讀理解
Why can we not see the yellow in a leaf during the summer?
There is so much green chlorophyll on top that it hides the yellow.
What does a tree do with its chlorophyll in autumn?
It stops making more, breaks it down, and moves the useful parts back into its branches.
What kind of weather makes the reddest leaves?
Bright days, and nights that are cool but not freezing.
Words & Phrases · 生字及片語
autumn(n.)秋天The leaves turn gold in autumn.葉子在秋天變成金黃色。season(n.)季節Which season do you like best?你最喜歡哪一個季節？color(n.)顏色The color was there all summer.那個顏色整個夏天都在。pigment(n.)色素A pigment gives a leaf its color.色素讓葉子有了顏色。fade(v.)褪色；逐漸消失The green begins to fade.綠色開始褪去。hidden(adj.)隱藏的The yellow was hidden under the green.黃色藏在綠色底下。bright(adj.)明亮的；鮮豔的Bright days make the leaves redder.晴朗的白天讓葉子更紅。cool(adj.)涼爽的Cool nights help to make red leaves.涼爽的夜晚有助於葉子變紅。
Quick Check · 小測驗
1. Why is a leaf green in summer?
2. Where does the yellow of an autumn leaf come from?
3. What does a tree do with its chlorophyll in autumn?
4. Which color is newly made in autumn?
5. What makes a leaf finally fall?
Mix It Yourself · 自己調調看
Three pigments, many colors 三種色素，很多種顏色
Slide each pigment up or down and watch the leaf. Start by taking away the green.
把每一種色素調多或調少，看葉子怎麼變。先從把綠色拿掉開始。
How much of each pigment? · 每種色素各有多少？
The mixing here uses the same simple rule as the model. Real leaves hold many more shades.這裡的混色用的是和模型同一套簡單的規則。真的葉子，色調要豐富得多。
The leaf looks · 這片葉子看起來
Try It in the Model · 在模型裡試試
Four moments in the year 一年裡的四個時刻
Yellow is uncovered, and red is made. That is the whole difference between a tree that turns gold and a tree that turns scarlet.
黃色是「露出來」的，紅色是「做出來」的。一棵變金黃的樹和一棵變火紅的樹，差別就在這裡。
Yellow shows through黃色露出來
Check the three bars. Has the yellow bar grown, or has something else changed?
看看那三條量表。是黃色那一條變長了，還是別的東西變了？
Red is made做出紅色
Now switch off Bright days, cool nights, and watch the leaf.
現在把「白天晴朗、夜裡涼」關掉，看看葉子。
Letting go放手
Watch the brown spot where the stalk meets the branch, and then the leaf.
盯著葉柄和樹枝相接處的那個咖啡色小點，再看葉子。
Go Further · 延伸閱讀
What the green is for, and why there are seasons 綠色是做什麼的，季節又是怎麼來的
Living Things · Lesson 2 · 生命與生態 第二課How Does a Leaf Make Food from Sunlight?葉子怎麼用陽光做出食物？See what chlorophyll does all summer.看看葉綠素整個夏天在忙什麼。Go to the lesson · 前往這一課 →Living Things · Lesson 7 · 生命與生態 第七課How Does Water Reach the Top of a Tree?水怎麼爬到樹頂？See the water supply that the cork layer shuts off.看看木栓層關掉的那條水路。Go to the lesson · 前往這一課 →
Color by the Numbers · 顏色的數字
Six numbers about autumn leaves 六個和秋葉有關的數字
How many pigments, how many trees, and for how long.
幾種色素、多少樹、持續多久。
3pigments · 種色素
Green chlorophyll, yellow and orange carotenoids, and red anthocyanins.綠色的葉綠素、黃色和橘色的類胡蘿蔔素、紅色的花青素。
2changes · 個變化
Autumn color comes from two things: losing the green, and in some trees gaining red.秋天的顏色來自兩件事：失去綠色，以及某些樹多了紅色。
10%make red · 會做紅色
In temperate regions, only about one tree species in ten makes the red pigment.在溫帶地區，大約每十種樹裡只有一種會製造紅色的色素。
70%in New England · 在新英格蘭
In a few places, most famously the northeastern United States, as many as this share of tree species make it.在少數地方（最有名的是美國東北部），會製造紅色色素的樹種可以高到這個比例。
1900the year · 年
Mikhail Tsvet invented a way to separate the pigments of a leaf, while studying plant colors.茨維特在研究植物的顏色時，發明了把葉子裡的色素分開來的方法。
1,100–2,600 mabove the sea · 海拔
The height of Aowanda in Nantou, one of Taiwan's well-known places for autumn leaves.南投奧萬大的海拔高度——台灣著名的賞楓地點之一。
Leaf Stories · 葉子的故事
A man named Color, a puzzle about red, trees that drop their leaves in the dry season, and a valley in Nantou 名字就叫「顏色」的人、紅色之謎、乾季落葉的樹，還有南投的一座山谷
What people have found out by looking closely at a leaf.
人們仔細看一片葉子之後發現的事。
1900
A man named Color名字就叫「顏色」的人
Mikhail Tsvet was a botanist who wanted to know what pigments a green leaf holds. In 1900 he found a way to pull them apart, so that the green, the yellow, and the orange each ended up in a different place. His method is called chromatography, and scientists everywhere still use it. His family name, Tsvet, is the Russian word for color.
茨維特是一位植物學家，他想知道綠色的葉子裡到底有哪些色素。1900 年，他找到一個把它們拆開的方法，讓綠色、黃色和橘色各自跑到不同的位置。這個方法叫做「層析法」，全世界的科學家到今天都還在用。他的姓氏 Tsvet，在俄文裡就是「顏色」的意思。
Open question · 還沒有定論
Why bother to make red?何必費力做紅色？
Yellow costs a tree nothing, because it was already there. Red is different. The tree has to spend sugar to make it, in leaves it is about to throw away. Why? Scientists have several ideas and have not settled the matter. One idea is that red works like a sunshade. It protects the leaf from strong light on cold days, so that the tree has more time to take its nutrients back.
黃色不花樹什麼力氣，因為它本來就在。紅色不一樣：樹得花掉糖才做得出來，而且是做在馬上就要丟掉的葉子上。為什麼？科學家有好幾種想法，還沒有定論。其中一種想法是，紅色像一把遮陽傘：在寒冷的日子裡替葉子擋住強光，讓樹有更多時間把養分收回去。
Tropics · 熱帶
Not only in autumn不只在秋天
Trees that drop all their leaves for part of the year are called deciduous. In cool countries they do it before winter. But in many warm parts of the world there is no cold winter, and trees there drop their leaves in the dry season, when water is short. Other trees, called evergreens, keep green leaves all year and replace them a few at a time.
一年裡有一段時間把葉子全部落光的樹，叫做落葉樹。在涼爽的國家，它們在冬天之前落葉。可是世界上很多溫暖的地方沒有寒冷的冬天，那裡的樹是在缺水的乾季落葉。另外一些樹叫做常綠樹，整年都有綠葉，葉子是一次換幾片、慢慢輪替的。
Taiwan · 台灣
The red valley of Aowanda奧萬大的紅色山谷
Aowanda National Forest Recreation Area lies in the mountains of Nantou, between 1,100 and 2,600 meters above the sea. It has a large natural forest of Formosan sweetgum, and every autumn these trees, with the maples near the visitor center, color the valley. Taiwan's Ministry of Agriculture explains that leaves of the same kind of tree change color sooner high in the mountains than they do lower down. That is one reason people in Taiwan go up into the mountains to see red leaves.
奧萬大國家森林遊樂區位在南投的山區，海拔 1,100 到 2,600 公尺之間。這裡有大片原生的楓香林，每年秋天，這些楓香和遊客中心附近的青楓一起把山谷染上顏色。農業部的農業知識入口網說明：同一種樹的葉子，在高海拔會比在低海拔先變色。這也是在台灣大家往山上去看紅葉的原因之一。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思Leaves turn yellow because the tree makes yellow in autumn.葉子變黃，是因為樹在秋天製造了黃色。
✓ Fact · 事實The yellow was there all summer. It shows when the green fades.黃色整個夏天都在，綠色褪去之後才看得見。
✗ Myth · 迷思Frost is what turns leaves red.葉子是被霜凍紅的。
✓ Fact · 事實The best reds come with bright days and cool nights that do not freeze.最漂亮的紅色出現在白天晴朗、夜裡涼而不結霜的時候。
✗ Myth · 迷思Autumn leaves are dying, and the tree is losing them.秋葉是快死了，樹正在失去它們。
✓ Fact · 事實The tree drops them on purpose, after taking back the useful parts.是樹主動讓它們掉落的，而且先把有用的東西收了回去。
✗ Myth · 迷思Every tree drops its leaves when it gets cold.天一冷，每一種樹都會落葉。
✓ Fact · 事實Evergreens keep their leaves, and in warm places many trees drop theirs in the dry season.常綠樹不會；在溫暖的地方，很多樹是在乾季落葉。
Remember It · 記憶口訣
Autumn color in a sentence 一句話記住秋天的顏色
Green hides the rest綠色蓋住其他顏色
Chlorophyll is on top all summer.
整個夏天，葉綠素都在最上面。
Yellow is uncovered黃色是露出來的
It was there the whole time.
它一直都在。
Red is made紅色是做出來的
From sugar, on bright, cool days.
用糖做的，在晴朗涼爽的日子。
Then the leaf is sealed off然後葉子被封住
A cork layer, and the leaf falls.
一層木栓，葉子就掉了。
Classroom Activity 1 · 課堂活動一
Pull the Colors Apart 把顏色拆開
You need · 準備材料
- Two or three green leaves, a coin, and strips cut from a white coffee filter兩三片綠葉、一枚硬幣，還有幾條從白色咖啡濾紙剪下來的紙條
- A small glass, a pencil, and a little rubbing alcohol, poured by an adult一個小玻璃杯、一支鉛筆，還有請大人倒的一點點藥用酒精
Steps · 步驟
- Lay a leaf across a paper strip, about two centimeters from one end. Roll the edge of the coin over it to press a dark green line onto the paper.把葉子橫放在紙條上，離一端大約兩公分。用硬幣的邊緣在上面滾壓，在紙上壓出一條深綠色的線。
- Ask an adult to pour alcohol into the glass, just enough to cover the bottom.請大人把酒精倒進杯子，蓋住杯底就夠了。
- Hang the strip from the pencil so that only its tip touches the alcohol. The green line must stay above the liquid.把紙條掛在鉛筆上，只讓最下面的尖端碰到酒精；那條綠線一定要在液面上方。
- Wait twenty minutes. What colors have traveled up the paper, and which one went farthest?等二十分鐘。有哪些顏色沿著紙條爬上去了？哪一種跑得最遠？
You should find a yellow band above the green one. That is the hidden pigment. Work near an open window, keep the alcohol away from flames and from your eyes, and let the adult put it away.
你應該會在綠色帶的上方看到一條黃色的帶子，那就是藏起來的色素。請在打開的窗戶旁邊做，酒精要遠離火源和眼睛，用完請大人收好。
Classroom Activity 2 · 課堂活動二
A Leaf Calendar 葉子的日曆
You need · 準備材料
- A tree near your home or school that drops its leaves住家或學校附近一棵會落葉的樹
- A notebook, colored pencils, and tape一本筆記本、色鉛筆和膠帶
Steps · 步驟
- Once a week, pick up one fallen leaf from under the tree and tape it into your notebook.每個星期一次，在樹下撿一片落葉，貼在筆記本裡。
- Write the date and the weather that week: sunny or cloudy, warm or cool.寫下日期，還有那個星期的天氣：晴天還是陰天，溫暖還是涼爽。
- Color a small square beside it to match the leaf as closely as you can.在旁邊畫一個小方格，盡量塗成和葉子一樣的顏色。
- After two months, look at the row of squares. When did the color change fastest?兩個月後，看看那一排小方格。顏色是在什麼時候變得最快？
Pick up fallen leaves only, and leave the ones on the tree. If your tree stays green, that is a result too. Some trees keep their leaves all year.
只撿掉在地上的葉子，樹上的不要摘。要是你的樹一直是綠的，那也是一個結果：有些樹整年都留著葉子。
Sources · 資料出處
Facts and numbers on this page were checked against these sources (October 2026). · 本頁的事實與數字依下列資料查證（2026 年 10 月）。
- Autumn color has two main components, losing the green of chlorophyll and gaining the red of anthocyanins; the yellow is due to carotenoids, already present in the leaf but masked by chlorophyll during summer; chlorophyll breaks down in use and is replenished through the growing season; in late summer, with shortening days and cooling temperatures, the plant begins recovering its nutritional investment in the leaves; anthocyanins are actively produced in autumn from sugars, most when days are bright and cool and nights are chilly but not freezing; they are present in about 10% of tree species in temperate regions and up to 70% in New England; a layer of cork cells forms at the base of each leaf; according to the photoprotection theory anthocyanins shield the leaf so the tree can reabsorb nutrients more efficiently秋色有兩個主要成分：失去葉綠素的綠、獲得花青素的紅；黃色來自類胡蘿蔔素，原本就在葉中，夏天被葉綠素遮住；葉綠素使用中會分解，生長季不斷補充；夏末日照縮短、氣溫下降，植物開始回收葉片中的養分；花青素在秋天由醣類主動合成，白天晴朗涼爽、夜間冷而不結冰時最多；溫帶約 10% 的樹種會產生花青素，新英格蘭可達 70%；葉柄基部形成木栓細胞層；光保護假說認為花青素替葉子遮光，讓樹更有效率地回收養分Wikipedia, “Autumn leaf color” ↗
- Chlorophyll absorbs mainly blue and red light, so tissues that contain it look green葉綠素主要吸收藍光與紅光，所以含葉綠素的組織看起來是綠色Wikipedia, “Chlorophyll” ↗
- Carotenoids are yellow, orange, and red pigments made by plants; they give carrots and corn their color類胡蘿蔔素是植物製造的黃、橘、紅色色素；紅蘿蔔與玉米的顏色來自它Wikipedia, “Carotenoid” ↗
- Mikhail Tsvet invented chromatography in 1900 during his research on plant pigments; his family name is the Russian word for color茨維特在 1900 年研究植物色素時發明層析法；他的姓氏在俄文中意為「顏色」Wikipedia, “Mikhail Tsvet” ↗
- In temperate climates leaf loss coincides with winter; in tropical, subtropical, and arid regions plants lose their leaves during the dry season溫帶地區的落葉發生在冬季；熱帶、亞熱帶與乾燥地區的植物在乾季落葉Wikipedia, “Deciduous” ↗
- An evergreen is a plant whose foliage stays green and working throughout the year常綠植物的葉子整年保持綠色並持續運作Wikipedia, “Evergreen” ↗
- Aowanda National Forest Recreation Area lies between 1,100 and 2,600 meters; its native Formosan sweetgum forest and the green maples near the visitor center color the park every autumn奧萬大國家森林遊樂區海拔 1,100–2,600 公尺；賞楓步道上大片的原生楓香林與遊客中心周遭的青楓等，每逢秋季將園區點綴得萬紫千紅農業部林業及自然保育署〈奧萬大國家森林遊樂區〉 Forestry and Nature Conservation Agency, Taiwan ↗
- When autumn comes and the days shorten and cool, less chlorophyll is made and the carotenoids take over; leaves of the same species change color sooner at high elevations than at low ones秋天日照縮短、氣溫降低，葉綠素製造減少，類胡蘿蔔素佔優勢，黃葉顯現；同一樹種的葉子，高海拔比低海拔優先變色農業部 農業知識入口網〈為什麼樹葉一到秋天就會變成不同的顏色?〉 Ministry of Agriculture, Taiwan ↗