A sunny day after rain下過雨的大晴天
The holes are wide open, and sugar pours out along the vein.
氣孔大開，糖沿著葉脈不斷送出去。
Living Things · Unit 1 · Lesson 2 · 生命與生態 單元一 第二課
How Does a Leaf Make Food from Sunlight?葉子怎麼用陽光做出食物？
A plant never eats, yet it grows from a tiny seed into a tall tree. Where does all that stuff come from? In a 3D model of a leaf cut open, give it light, air, and water, and watch it make sugar and give off oxygen. Take one of the three away and see what happens. Then find out why almost everything you eat began as sunlight on a leaf.
植物從來不吃東西，卻能從一顆小小的種子長成一棵大樹。那麼多的東西是從哪裡來的？在一片切開的葉子的 3D 模型裡，給它光、空氣和水，看它怎麼做出糖、放出氧氣。再拿掉其中一樣，看看會怎麼樣。最後找出答案：為什麼你吃的東西，幾乎每一樣最初都是照在葉子上的陽光？
Big idea · 一句話看懂
A leaf is a food factory that runs on sunlight. It takes in carbon dioxide from the air and water from the roots. With the energy of light, it joins them into sugar, and it gives off oxygen. The plant uses the sugar to live and to grow. The leaf needs all three things at once: light, carbon dioxide, and water. Whichever one is shortest sets the speed.
葉子是一座用陽光發動的食物工廠。它從空氣裡吸進二氧化碳，從根部得到水，再用光的能量把它們結合成糖，同時放出氧氣。植物靠這些糖活著、長大。葉子同時需要三樣東西：光、二氧化碳和水；最缺的那一樣，決定它做得多快。
3D Model · 3D 模型
Inside a Leaf 葉子裡面
Drag to turn the model, and scroll or pinch to zoom. This is a slice of a leaf, seen from the side and made much larger. Follow the five kinds of dots: yellow light, gray carbon dioxide, blue water, orange sugar, and pale green oxygen. Then move the three sliders one at a time. What happens to the sugar when you turn the light down? What happens to the little holes underneath when you take the water away?
拖曳可以旋轉模型，滾輪或雙指可以縮放。這是一片葉子的切面，從側面看，而且放大了很多倍。跟著五種小點走：黃色是光、灰色是二氧化碳、藍色是水、橘色是糖、淺綠色是氧氣。接著一次只動一支滑桿：把光調暗，糖怎麼了？把水拿掉，底下那些小孔又怎麼了？
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。
- Yellow dots: sunlight
黃色的點：陽光 - Gray dots: carbon dioxide coming in
灰色的點：進來的二氧化碳 - Blue dots: water coming in along the vein
藍色的點：沿著葉脈進來的水 - Orange cubes: sugar going out along the vein
橘色小方塊：沿著葉脈送出去的糖 - Pale green dots: oxygen going out
淺綠色的點：出去的氧氣 - Dark green balls: chloroplasts, where the sugar is made
深綠色小球：葉綠體，做糖的地方
A teaching model. A real leaf is only a fraction of a millimeter thick, and this slice is drawn very much larger and far tidier than a real one. The percentages on the sliders are not measurements; they only mean a little or a lot. The rule that the shortest supply sets the speed is a simple picture of something more complicated. The counts of sugar and oxygen follow the real recipe: six oxygen for every sugar. Light is not really made of dots that pile up in a leaf.
這是教學用的模型。真的葉子只有零點幾公釐厚，這個切面畫得大了非常多倍，也比真的整齊得多。滑桿上的百分比不是測量值，只代表「少」或「多」。「最缺的那一樣決定速度」是把比較複雜的事情簡化之後的說法。糖和氧氣的數目照的是真的配方：每做一顆糖，放出六個氧氣。光其實也不是一顆一顆堆在葉子裡的小點。
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
2
Unit 2: How Does a Leaf Make Food from Sunlight?
You have to eat to stay alive. So does a dog, a bird, and a fish. But a tree stands in one place for a hundred years and never eats a thing. All the same, it grows. A seed that weighs less than a coin becomes a trunk too heavy to lift. Where does all that wood come from?
你必須吃東西才能活下去，狗、鳥和魚也一樣。可是一棵樹在同一個地方站了一百年，從來沒有吃過任何東西，卻照樣長大。一顆比硬幣還輕的種子，可以長成重到搬不動的樹幹。那麼多的木頭是從哪裡來的？
For a long time people thought the answer was the soil. About four hundred years ago, a scientist named Jan van Helmont tested the idea. He planted a small willow tree in a pot of soil and gave it nothing but water for five years. The tree gained about 74 kilograms. The soil had lost only 57 grams. So the tree was not made of soil.
很長一段時間，人們以為答案是土壤。大約四百年前，一位叫做范．海爾蒙特的科學家做了實驗來檢驗這個想法。他把一棵小柳樹種在一盆土裡，五年當中只給它澆水。這棵樹增加了大約 74 公斤，土卻只少了 57 公克。所以樹並不是土做的。
The real answer is in the leaves. A leaf takes in a gas called carbon dioxide from the air, through tiny holes on its underside. Water comes up from the roots. Inside the leaf there are small green parts called chloroplasts. They catch the energy of sunlight and use it to join the carbon dioxide and the water into sugar.
真正的答案在葉子裡。葉子透過背面細小的孔，從空氣中吸進一種叫做二氧化碳的氣體；水則從根部送上來。葉子裡面有一些綠色的小東西，叫做葉綠體。它們抓住陽光的能量，用它把二氧化碳和水結合成糖。
This is called photosynthesis, which means putting together with light. Sugar is the plant's food. It burns some for energy, and it builds the rest into leaves, roots, and wood. So most of a tree is made from air and water, joined together by sunlight.
這件事叫做「光合作用」，意思是「用光來合成」。糖就是植物的食物：一部分燒掉當作能量，其餘的拿來長出葉子、根和木頭。所以一棵樹的大部分，是空氣和水做的，是陽光把它們接在一起的。
Something is left over when sugar is made: oxygen. The leaf lets it out through the same tiny holes, and it mixes into the air. That oxygen comes from the water, not from the carbon dioxide. It is the gas that you, and nearly every other animal, must breathe to stay alive.
做糖的時候會多出一樣東西：氧氣。葉子從同樣那些小孔把它放出去，混進空氣裡。這些氧氣是從水來的，不是從二氧化碳來的。它就是你和幾乎所有動物都必須呼吸才能活下去的那種氣體。
Now think about your last meal. Rice, bread, and vegetables are parts of plants. Meat and eggs come from animals that ate plants. Follow any food back far enough, and you arrive at a green leaf in the sun. In a way, you run on sunlight too.
現在想一想你上一餐吃了什麼。米飯、麵包和青菜是植物的一部分；肉和蛋來自吃植物的動物。任何一種食物，只要往回追得夠遠，都會追到一片曬著太陽的綠葉。從某個角度來說，你也是靠陽光在運轉的。
Read aloud · 課文朗讀
Questions · 閱讀理解
What did van Helmont's willow tree show?
The tree gained about 74 kilograms while the soil lost only 57 grams, so a tree is not made of soil.
What three things does a leaf need to make sugar?
It needs light, carbon dioxide from the air, and water from the roots.
Where does the oxygen that a leaf gives off come from?
It comes from the water. It is left over when the leaf joins water and carbon dioxide into sugar.
Words & Phrases · 生字及片語
leaf(n.)葉子A green leaf fell from the tree.一片綠葉從樹上掉下來。sunlight(n.)陽光Plants need sunlight to grow.植物需要陽光才能生長。sugar(n.)糖A leaf makes sugar from air and water.葉子用空氣和水做出糖。oxygen(n.)氧氣We breathe in oxygen.我們吸進氧氣。carbon dioxide(n.)二氧化碳Leaves take in carbon dioxide from the air.葉子從空氣中吸收二氧化碳。root(n.)根The roots take up water from the soil.根從土壤裡吸水。energy(n.)能量Food gives your body energy.食物提供身體能量。factory(n.)工廠A leaf is like a small food factory.葉子就像一座小小的食物工廠。
Quick Check · 小測驗
1. What does a leaf make in photosynthesis?
2. Where does a leaf get its carbon dioxide?
3. What gives the leaf the energy to make sugar?
4. A plant has bright light and plenty of air but very little water. What happens?
5. What is most of a tree made from?
Work It Out · 算算看
The recipe for sugar 做糖的配方
Photosynthesis follows an exact recipe. Choose how many sugars the leaf should make, and count what it needs and what is left over.
光合作用有一份精確的配方。選一選葉子要做幾顆糖，再數一數它需要什麼、又多出了什麼。
Goes in · 放進去
Comes out · 做出來
The sugar here is glucose. Each dot stands for one molecule, the smallest bit of a substance. A real leaf makes an enormous number of them every second, and it needs light for every one.這裡的糖是葡萄糖。每一個點代表一個分子，也就是一種物質最小的一份。真的葉子每一秒都做出數量龐大的分子，而且每一個都需要光。
The leaf needs · 葉子需要
6 carbon dioxide · 二氧化碳
6 water · 水
And it makes · 做出
1 sugar · 糖（葡萄糖）
6 oxygen · 氧氣
The recipe never changes: 6 carbon dioxide and 6 water make 1 sugar and 6 oxygen. Nothing is lost. Every atom that goes in comes out again in the sugar or in the oxygen.這份配方永遠不變：6 個二氧化碳加 6 個水，做出 1 顆糖和 6 個氧氣。什麼都沒有少：放進去的每一個原子，都在糖或氧氣裡面。
Try It in the Model · 在模型裡試試
Four kinds of day 四種日子
On the cloudy day, try adding more water or more carbon dioxide. Does the sugar go up? Only the thing in shortest supply can speed the leaf up.
在陰暗的日子裡，試著多加一點水或二氧化碳：糖有變多嗎？只有補上最缺的那一樣，葉子才快得起來。
A dark, cloudy day陰暗的日子
Air and water are waiting, but there is not enough energy to join them.
空氣和水都在等，可是沒有足夠的能量把它們接起來。
A hot, dry day又熱又乾的日子
The holes close to save water, and the carbon dioxide is shut out.
氣孔關起來省水，二氧化碳也被擋在外面。
Night夜晚
The factory stops. The counters stand still until morning.
工廠停工，數字不再增加，要等到天亮。
Go Further · 延伸閱讀
The same gases, seen from two other lessons 同樣的氣體，從另外兩課來看
Earth and Weather · Lesson 16 · 地球與天氣 第十六課What Is the Greenhouse Effect?溫室效應是什麼？What carbon dioxide does in the air before a leaf takes it in.二氧化碳被葉子吸進去以前，在空氣裡做了什麼。Go to the lesson · 前往這一課 →The Human Body · Lesson 21 · 人體探索 第二十一課Where Does Your Energy Come From?你的力氣從哪裡來？What your body does with the sugar that plants made.植物做出來的糖，到了你的身體裡怎麼變成力氣。Go to the lesson · 前往這一課 →
Leaves by the Numbers · 葉子的數字
Six numbers about photosynthesis 六個和光合作用有關的數字
From one sugar to the whole planet.
從一顆糖，到整顆地球。
3things · 樣東西
A leaf needs light, carbon dioxide, and water, all at the same time.葉子同時需要光、二氧化碳和水。
6 + 6the recipe · 配方
Six carbon dioxide and six water make one sugar and six oxygen.6 個二氧化碳加 6 個水，做出 1 顆糖和 6 個氧氣。
74 kggained · 增加
Van Helmont's willow gained about this much in five years, while its soil lost only 57 grams.范．海爾蒙特的柳樹五年裡大約增加了這麼多，土卻只少了 57 公克。
1779the year · 年
Jan Ingenhousz showed that plants need light to do this, and that only their green parts do it.英根豪斯證明植物要有光才做得到這件事，而且只有綠色的部分會做。
3–6%of the light · 的光
Plants usually turn only about this much of the light that falls on them into stored energy.照在植物上的光，通常大約只有這麼多被轉成儲存起來的能量。
100+billion tons · 十億噸
Each year, plants and other living things that use light turn about 100 to 115 billion tons of carbon into living material.每一年，植物和其他會利用光的生物，把大約 1,000 到 1,150 億噸的碳變成生物體的一部分。
Leaf Stories · 葉子的故事
The willow, the bubbles, the color green, and the rice in your bowl 一棵柳樹、一串氣泡、綠色，還有你碗裡的飯
How people worked it out, and where you can see it today.
人們是怎麼弄懂的，還有今天在哪裡看得到。
1600s · 十七世紀
The willow in the pot盆子裡的柳樹
Jan van Helmont weighed a pot of soil, planted a small willow in it, and watered it for five years. Then he weighed everything again. The tree had gained about 74 kilograms, and the soil had lost only 57 grams. He decided that the tree was made of water. He was half right. He did not know that the air was giving it something too.
范．海爾蒙特先秤了一盆土的重量，在裡面種下一棵小柳樹，澆了五年的水，然後把所有東西重新秤一次。樹大約增加了 74 公斤，土只少了 57 公克。他的結論是：樹是水做的。他對了一半。他不知道，空氣也給了這棵樹東西。
1779
Bubbles in the sun陽光下的氣泡
Jan Ingenhousz put green plants under water and watched. In sunlight, small bubbles rose from the green parts. In the shade, the bubbles stopped. The plants were making a gas, and they needed light to do it. That was the missing piece. In the 1900s, another scientist, Cornelis van Niel, showed that the oxygen in those bubbles comes from water that the plant has split apart.
英根豪斯把綠色的植物放在水裡觀察。在陽光下，綠色的部分冒出一顆顆小氣泡；到了陰影裡，氣泡就停了。植物正在製造一種氣體，而且需要光才做得到。這就是缺少的那一塊拼圖。到了二十世紀，另一位科學家范尼爾證明，氣泡裡的氧氣來自被植物拆開的水。
Color · 顏色
Why leaves are green葉子為什麼是綠的
Sunlight is a mix of many colors. The green stuff in a leaf, called chlorophyll, takes in mostly the blue light and the red light and uses their energy. It takes in much less of the green, so the green light bounces off and reaches your eyes. The color you see is the part of the sunlight that the leaf uses least.
陽光是很多種顏色混在一起的。葉子裡綠色的東西叫做葉綠素，它主要吸收藍光和紅光，利用它們的能量；綠光吸收得少得多，所以被反射出來、進到你的眼睛。你看到的顏色，其實是陽光裡葉子用得最少的那一部分。
Changhua · 彰化
The rice in your bowl你碗裡的飯
Changhua County grows so much rice that it has been called the rice barn of Taiwan. Stand beside a paddy field on a sunny day, and you are looking at this lesson at work. Every leaf is taking in air and water and making sugar. The plant packs that sugar into its seeds as starch, and those seeds are the grains of rice in your bowl.
彰化縣盛產稻米，有「臺灣米倉」的稱號。大晴天站在稻田旁邊，你看到的就是這一課正在發生的事：每一片葉子都在吸進空氣和水、做出糖。稻子再把這些糖變成澱粉，存進種子裡；那些種子，就是你碗裡的一粒粒米飯。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思Plants get their food from the soil.植物的食物是從土裡來的。
✓ Fact · 事實Plants make their own food from air and water, using light. From the soil they take water and small amounts of minerals.植物用光，把空氣和水做成自己的食物。它們從土裡吸收的是水和少量的礦物質。
✗ Myth · 迷思A tree is made mostly of soil.一棵樹大部分是土做的。
✓ Fact · 事實Most of a tree is made from carbon dioxide and water. Van Helmont's soil lost only 57 grams while his tree gained 74 kilograms.樹的大部分是二氧化碳和水做的。范．海爾蒙特的土只少了 57 公克，樹卻增加了 74 公斤。
✗ Myth · 迷思The oxygen that leaves give off comes from carbon dioxide.葉子放出來的氧氣是從二氧化碳來的。
✓ Fact · 事實It comes from water. The plant splits water apart, keeps what it needs, and lets the oxygen go.它是從水來的。植物把水拆開，留下需要的部分，把氧氣放掉。
✗ Myth · 迷思Leaves are green because they use green light.葉子是綠的，因為它們用的是綠光。
✓ Fact · 事實It is the opposite. Leaves use mostly blue and red light. Green is the color they use least, so it is the color that bounces back.正好相反。葉子主要用的是藍光和紅光；綠光用得最少，所以被反射回來。
Remember It · 記憶口訣
Photosynthesis in a sentence 一句話記住光合作用
Air comes in空氣進來
Carbon dioxide, through tiny holes.
二氧化碳，從小孔進來。
Water comes up水送上來
From the roots, along the veins.
從根部，沿著葉脈。
Light joins them光把它們接起來
Sugar is made in the green parts.
綠色的部分做出糖。
Oxygen goes out氧氣出去
Left over from the water.
是水剩下來的。
Classroom Activity 1 · 課堂活動一
Bubbles from a Leaf 葉子冒泡泡
You need · 準備材料
- A clear glass or bowl of water and a fresh green leaf (a water plant works best)一個裝了水的透明杯子或碗，還有一片新鮮的綠葉（水草效果最好）
- A sunny windowsill, a dark cupboard, and a clock一個曬得到太陽的窗台、一個黑暗的櫃子，還有時鐘
Steps · 步驟
- Put the leaf under the water. Use a small stone to hold it down if it floats.把葉子放進水裡。如果它浮起來，用一顆小石頭壓住。
- Stand the glass in bright sunlight for one hour. Look closely at the leaf. What do you see on it?把杯子放在明亮的陽光下一個小時。仔細看葉子：上面出現了什麼？
- Tap the glass gently and wipe the bubbles off. Now put it in the dark cupboard for one hour.輕輕敲一敲杯子，把氣泡抹掉。然後把它放進黑暗的櫃子裡一個小時。
- Look again. Are there as many bubbles as before? What made the difference?再看一次。氣泡和剛才一樣多嗎？差別是什麼造成的？
This is the experiment Ingenhousz did in 1779. The bubbles in sunlight are mostly oxygen. Some bubbles may also form just because the water warms up, so compare the sunny glass with the dark one before you decide.
這就是英根豪斯在 1779 年做的實驗。陽光下的氣泡大部分是氧氣。不過水變暖本身也會冒出一些氣泡，所以要拿曬太陽的那一杯和放在暗處的那一杯比過，再下結論。
Classroom Activity 2 · 課堂活動二
A Leaf in the Dark 見不到光的葉子
You need · 準備材料
- A healthy potted plant with large leaves一盆葉子比較大的健康盆栽
- Black paper or aluminum foil, and paper clips黑紙或鋁箔紙，還有迴紋針
Steps · 步驟
- Choose one leaf and leave it on the plant. Cover part of it, on both sides, with a strip of black paper, and hold the paper in place with paper clips.選一片葉子，不要摘下來。用一條黑紙把它的一部分上下兩面都遮住，用迴紋針固定。
- Leave the plant in a sunny place for one week. Water it as usual.把盆栽放在曬得到太陽的地方一個星期，照平常那樣澆水。
- Take the paper off. Compare the part that was covered with the rest of the leaf.把黑紙拿掉。比一比被遮住的部分和葉子的其他部分。
- What color is the covered part? What do you think happened to it?被遮住的地方是什麼顏色？你覺得它發生了什麼事？
The covered part could not make any food, and the plant stopped keeping it green. Take the clips off gently, and the leaf will usually recover in the light. Use a plant that belongs to you or to your class.
被遮住的部分沒辦法做出食物，植物也不再讓它保持綠色。輕輕把迴紋針拿掉，葉子曬到光之後通常會慢慢恢復。請用自己或班上的盆栽來做。
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）。
- Photosynthesis turns light energy into chemical energy, splitting water to release oxygen and fixing carbon dioxide into sugar; discovered in 1779 by Jan Ingenhousz, who showed that plants need light; plants usually convert 3 to 6% of light; about 100 to 115 billion tons of carbon become biomass each year光合作用把光能轉成化學能，分解水放出氧氣，並把二氧化碳固定成糖；1779 年由英根豪斯發現，他證明植物需要光；植物通常把 3–6% 的光轉成化學能；每年約 1,000–1,150 億噸的碳變成生物量Wikipedia, “Photosynthesis” ↗
- Van Helmont's five-year willow experiment: the tree gained about 74 kg while the soil lost only 57 grams, and he concluded that the gain came from water范．海爾蒙特的五年柳樹實驗：樹增加約 74 公斤，土只少了 57 公克；他推論增加的重量來自水Wikipedia, “Jan Baptist van Helmont” ↗
- In sunlight, plants under water give off bubbles from their green parts, and in the shade the bubbles stop在陽光下，水中植物的綠色部分會冒出氣泡，在陰影中氣泡就停止Wikipedia, “Jan Ingenhousz” ↗
- Plants give off oxygen by splitting water, not carbon dioxide植物放出的氧氣來自分解水，而不是二氧化碳Wikipedia, “C. B. van Niel” ↗
- A stoma is a pore in the skin of a leaf, bordered by two guard cells that control how wide it opens; gases pass through it, and water vapor leaves through it氣孔是葉子表皮上的小孔，由兩個保衛細胞控制開合；氣體經由它進出，水氣也從這裡散失Wikipedia, “Stoma” ↗
- Chlorophyll absorbs mainly blue and red light, and green light is absorbed less, which is why plants look green葉綠素主要吸收藍光和紅光，綠光吸收得比較少，所以植物看起來是綠色的Wikipedia, “Chlorophyll” ↗
- In most leaves the main food-making tissue is a layer of tall cells on the upper side大部分的葉子，主要進行光合作用的組織是靠近上表面的柵狀組織Wikipedia, “Leaf” ↗
- Changhua County is known for its rice and has been called the rice barn of Taiwan彰化縣盛產稻米，有「臺灣米倉」之譽維基百科「彰化縣」（引《田中鎮志》） ↗