Skin cell皮膚細胞
They fit together like paving stones and are replaced all the time.
它們像石板一樣拼在一起，而且不斷汰舊換新。
The Human Body · Lesson 24 · 人體探索 第24課
What Are You Made Of?你是什麼做成的？
Zoom in on your hand, ten times closer at every step: skin, cells, the nucleus, and at last the DNA inside. Then work out how long it would take to count your cells.
把鏡頭對著你的手，每一步都拉近十倍：皮膚、細胞、細胞核，最後是裡面的 DNA。再算一算，要數完你的細胞得花多久。
Big idea · 一句話看懂
You are made of trillions of tiny living cells. Every one came from another cell, and almost every one carries the same set of instructions, your DNA.
你是由幾十兆個小小的、活的細胞組成的；每一個都來自另一個細胞，而幾乎每一個都帶著同一套說明書——你的 DNA。
3D Model · 3D 模型
Ten Times Closer 再近十倍
Press play, or drag the slider. Every step makes things ten times bigger. You begin with a whole skeleton and dive into the back of the hand: skin, the tiny ridges on it, a layer of cells, one cell, the nucleus in its middle, and finally the twisted ladder of DNA. Watch the yellow bar under the model: the panel on the right tells you how long it is and what else is that size. At the cell, try the four cell types.
按播放，或是拖動滑桿。每一步都把東西放大十倍。你從一整副骨架出發，朝著手背一路鑽進去：皮膚、皮膚上細細的紋路、一層細胞、一個細胞、細胞中間的細胞核，最後是像扭轉的梯子一樣的 DNA。注意看模型下面那條黃色的橫條：右邊的面板會告訴你它有多長，還有什麼東西也是這麼大。到了細胞那一站，試試四種不同的細胞。
Loading… · 載入中…
Drag to turn · 拖曳旋轉 Scroll or pinch to zoom · 滾輪／雙指縮放
Magnified 1 times · 放大 1 倍
This 3D model needs WebGL, which this browser does not support. The counting and paper tools and the cards below still work.
這個瀏覽器不支援 WebGL，無法顯示 3D 模型；下方的數細胞、量紙工具和卡片一樣能用。
Count your cells · 數一數你的細胞
About 30 trillion cells. How fast can you count?大約 30 兆個細胞。你數得多快？
—years to count them all年才數得完
While this page has been open, a grown-up's body has made about 0 new red blood cells.這一頁打開到現在，一個大人的身體大約已經造了 0 個新的紅血球。
How thick is one sheet? · 一張紙有多厚？
—mm for one sheet一張紙的厚度（公釐）
- Pink bubble: the cell membrane
粉紅色的泡泡：細胞膜 - Purple ball: the nucleus
紫色的球：細胞核 - Orange beans: mitochondria, the power stations
橘色的豆子：粒線體，細胞的發電廠 - Gold beads: spools that DNA is wound on
金色的珠子：纏著 DNA 的線軸 - Twisted ladder: DNA
扭轉的梯子：DNA
The skeleton and the hand bones are real shapes from BodyParts3D. Everything smaller is our own drawing, with the sizes kept roughly right at each step. Real cells are crowded with far more parts than we show, they have no bright colors, and nothing inside them holds still. A real nucleus holds about two meters of DNA; we show a few short pieces.
骨架和手的骨頭是 BodyParts3D 的真實形狀。更小的東西都是本站自繪的示意圖，每一站的大小比例大致是對的。真正的細胞裡擠滿了比這裡多得多的零件，沒有鮮豔的顏色，裡面的東西也沒有一刻是靜止的。真正的細胞核裡裝著大約兩公尺長的 DNA；這裡只畫了短短的幾段。
Bone model: BodyParts3D, © The Database Center for Life Science, licensed under CC BY 4.0. We selected the bones, simplified the shapes, and turned the model upright; the skin, the cells, and everything inside them are our own drawing. · 骨骼模型來源：BodyParts3D（日本生命科學資料庫中心，CC BY 4.0 授權）；本站挑選骨頭、簡化形狀並轉正方向，皮膚、細胞與細胞裡的一切為本站自繪示意。
Reading · 英文閱讀
24
Unit 24: What Are You Made Of?
Look closely at the back of your hand. Your skin looks like one smooth sheet. But if you could shrink until a grain of sand looked as big as a house, you would see something surprising. Your skin is not one sheet at all. It is built from tiny pieces fitted together, like the stones of a path. Each piece is called a cell.
仔細看看你的手背。皮膚看起來是完整光滑的一片。可是，如果你能一直縮小，小到一粒沙看起來像一棟房子那麼大，你會看到一件意想不到的事：皮膚根本不是「一片」。它是用很小很小的一塊一塊拼起來的，就像小路上的石板。每一塊叫做一個細胞。
A cell is the smallest part of you that is alive. It takes in food and oxygen, it uses energy, and it can make a copy of itself. Most cells are far too small to see: you could line up several of them across the width of a single hair. That is why nobody knew about cells until the microscope was invented. In 1665, an English scientist named Robert Hooke looked at a thin slice of cork and saw rows of tiny empty boxes. They reminded him of the small rooms where monks lived, so he called them “cells.”
細胞是你身上「活著」的最小單位。它吸收食物和氧氣、使用能量，還能複製出另一個自己。大部分的細胞都小到看不見：一根頭髮的寬度，就可以並排放好幾個。所以在顯微鏡發明之前，沒有人知道細胞的存在。1665 年，英國科學家虎克（Robert Hooke）觀察一片薄薄的軟木塞，看到一排排小小的空格子，讓他想起修道士住的小房間，於是把它們叫做 cell（小房間）。
How many cells do you have? A grown-up has about 30 trillion. A trillion is a million millions. If you counted one cell every second, without stopping to eat or sleep, you would need nearly a million years to finish.
你有多少個細胞呢？一個大人大約有 30 兆個。一兆是一百萬個一百萬。如果你一秒鐘數一個，不吃飯也不睡覺，要將近一百萬年才數得完。
A cell has parts, just as your body has organs. A thin skin called the membrane holds the cell together and decides what goes in and out. Inside are tiny power stations called mitochondria. Remember how your cells burn sugar with oxygen to get energy? The mitochondria are where that happens. And in the middle sits the nucleus, the control room.
就像身體有器官，細胞也有自己的零件。一層薄薄的皮叫做細胞膜，把細胞包起來，也決定什麼東西可以進出。裡面有小小的發電廠，叫做粒線體。還記得細胞用氧氣把糖燒掉來得到能量嗎？那件事就是在粒線體裡發生的。正中間坐著的是細胞核——控制室。
Inside the nucleus is the most amazing thing of all: DNA. DNA looks like a very long, twisted ladder. The rungs of the ladder come in four kinds, and their order is a code, like letters in a book. This book holds the instructions for building you and keeping you running. Almost every one of your cells carries a full copy of it. If you could pull the DNA from just one cell out straight, it would be about two meters long!
細胞核裡面，有最神奇的東西：DNA。DNA 看起來像一座非常長、扭轉起來的梯子。梯子的橫槓有四種，它們排列的順序就是一套密碼，就像書裡的字。這本書記載的，是怎麼建造你、怎麼讓你運作的說明。你幾乎每一個細胞裡，都有完整的一本。如果能把一個細胞裡的 DNA 拉直，它大約有兩公尺長！
Your cells are not all alike. A red blood cell is a soft red disc that carries oxygen. A nerve cell has a long wire for sending messages. A muscle cell is a long fiber that can pull. Yet they all follow the same book of instructions: each kind simply reads different pages. And every one of them came from another cell that split in two. That is how you grow, and how a cut heals. So what are you made of? Trillions of tiny living things, all working together. Zoom in on the model above and meet them.
你的細胞並不是每個都一樣。紅血球是軟軟的紅色圓盤，負責載氧氣；神經細胞有一條長長的線，用來傳遞訊息；肌肉細胞是一條會拉的長纖維。可是它們照的都是同一本說明書——只是每一種細胞讀的頁數不一樣。而且，每一個細胞都是由另一個細胞一分為二得來的；你就是這樣長大的，傷口也是這樣癒合的。所以，你是什麼做成的？是幾十兆個小小的生命，全部一起合作。到上面的模型裡把鏡頭拉近，去認識它們吧。
Read aloud · 課文朗讀
Questions · 閱讀理解
What is a cell?
The smallest part of you that is alive. It takes in food and oxygen, uses energy, and can make a copy of itself.
What are the jobs of the membrane, the mitochondria, and the nucleus?
The membrane holds the cell together and decides what goes in and out. The mitochondria burn sugar to make energy. The nucleus is the control room.
What is DNA, and where is it kept?
DNA is a very long, twisted ladder whose rungs spell out the instructions for building you and keeping you running. It is kept in the nucleus.
Words & Phrases · 生字及片語
cell(n.)細胞Your body is made of trillions of cells.你的身體是由幾十兆個細胞組成的。tiny(adj.)非常小的An ant is tiny, but a cell is much smaller.螞蟻很小，但細胞比牠小得多。microscope(n.)顯微鏡We looked at onion skin under a microscope.我們用顯微鏡觀察洋蔥皮。trillion(n.)兆A trillion is a million millions.一兆是一百萬個一百萬。nucleus(n.)細胞核The nucleus is the control room of the cell.細胞核是細胞的控制室。instructions(n.)說明；指示Read the instructions before you build the model.組模型之前，先讀說明書。copy(n.)複製品；一份Please make a copy of this page.請把這一頁影印一份。alive(adj.)活著的The plant is still alive: look at the new leaf.這棵植物還活著：你看那片新葉子。
Quick Check · 小測驗
1. What is the smallest living part of your body?
2. Why did Robert Hooke choose the word “cell”?
3. About how many cells does a grown-up have?
4. Which part of the cell burns sugar to make energy?
5. What does DNA look like?
Cell Types · 細胞的種類
One instruction book, many kinds of cells 同一本說明書，很多種細胞
Think of a school with one big library. The cook, the nurse, and the music teacher all use the same library, but each one reads different books. Your cells share one set of DNA in the same way: each kind reads the pages it needs.
想像一所學校只有一間大圖書館。廚房阿姨、護理師、音樂老師用的都是同一間圖書館，可是每個人讀的書不一樣。你的細胞就是這樣共用同一套 DNA：每一種細胞只讀它需要的那幾頁。
Red blood cell紅血球
It has no nucleus and lives for about a hundred days. Most of the cells in your body are red blood cells.
它沒有細胞核，大約活一百多天。你身上的細胞，大部分都是紅血球。
Nerve cell神經細胞
One long wire, many short branches. You met them in the lesson about the brain.
一條長長的線，很多短短的分支。你在大腦那一課見過它們。
Muscle cell肌肉細胞
A long striped fiber with many nuclei. Thousands of them side by side make a muscle.
一條有條紋的長纖維，裡面有很多個細胞核。成千上萬條並排在一起，就是一條肌肉。
Bone cell骨細胞
Some build new bone and some clear away old bone. That is how a broken bone heals.
有的負責造新的骨頭，有的負責清掉舊的。骨折就是這樣癒合的。
Measure Yourself · 親身測量
How do you measure something too thin to measure? 太薄的東西，要怎麼量？
A cell is too small for a ruler. So is one sheet of paper. But scientists have a trick for thin things, and you can use it too, with the tool below the model.
細胞太小了，尺量不出來；一張紙也是。不過科學家有一個量薄東西的方法，你也可以用——就在模型下方的工具裡。
- 📚Stack · 疊起來Count out 100 sheets of the same paper (the pages of a thick book work well: 100 sheets are 200 pages).數出 100 張同樣的紙（一本厚書的內頁就很好用：100 張是 200 頁）。
- 📏Measure · 量一量Press the stack flat and measure how thick it is, in millimeters.把那一疊壓平，量它有幾公釐厚。
- ➗Divide · 除一除Type the numbers into the tool. It divides for you and tells you how many cells would fit across one sheet.把數字輸入工具。它會幫你除，並告訴你一張紙的厚度可以並排放幾個細胞。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思Cells are flat, like the pictures in a book.細胞是扁平的，就像書上畫的那樣。
✓ Fact · 事實Pictures are flat, but cells are not. They are tiny three-dimensional bags, balls, discs, and fibers.圖是平的，細胞可不是。它們是立體的小袋子、小球、圓盤和纖維。
✗ Myth · 迷思All the cells in your body look the same.身體裡所有的細胞都長得一樣。
✓ Fact · 事實Scientists count hundreds of kinds, each with a shape that fits its job.科學家算出有好幾百種，每一種的形狀都配合它的工作。
✗ Myth · 迷思You keep the same cells all your life.你一輩子用的都是同一批細胞。
✓ Fact · 事實Many are replaced all the time. A red blood cell lasts only about 100 to 120 days.很多細胞一直在汰換。一個紅血球大約只能用 100 到 120 天。
✗ Myth · 迷思Every cell in and on your body is your own.你身體裡裡外外的每一個細胞，都是你自己的。
✓ Fact · 事實About as many bacteria live in and on you as you have cells of your own. Most of them are in your gut, and most do you no harm.住在你身體裡和身上的細菌，數目和你自己的細胞差不多。它們大部分住在腸子裡，而且大多對你沒有害處。
Remember It · 記憶口訣
Cells in a sentence 一句話記住細胞
Cell means small roomcell 就是小房間
Hooke saw tiny boxes in cork in 1665 and named them after monks' rooms.
1665 年，虎克在軟木塞裡看到小格子，用修道士的小房間替它們命名。
About 30 trillion大約 30 兆個
Counting one a second would take nearly a million years.
一秒數一個，要將近一百萬年。
Wall, power, control牆、發電廠、控制室
Membrane, mitochondria, nucleus.
細胞膜、粒線體、細胞核。
DNA is the instruction bookDNA 是說明書
A twisted ladder in the nucleus, with a full copy in almost every cell.
細胞核裡一座扭轉的梯子，幾乎每個細胞都有完整的一份。
In Chinese · 中文怎麼說
Small Rooms and Tiny Sacs 小房間和小胞
The English word “cell” means a small room. So how did it become 細胞 (xìbāo) in Chinese? In 1858, the Chinese mathematician Li Shanlan and the Scottish missionary Alexander Williamson translated a book about plants. For “cell” they wrote 細胞: 細 means tiny, and 胞 is a sac that holds something living. The word traveled to Japan, became the usual term there, and later came back to China. The same 胞 appears in 同胞 (tóngbāo), which means brothers and sisters, or the people of your own country: literally, “those from the same sac.” In that sense, your 30 trillion cells really are 同胞. They are one family, and they all carry the same book.
英文的 cell 意思是小房間，那它到了中文怎麼變成「細胞」的呢？1858 年，中國數學家李善蘭和蘇格蘭傳教士韋廉臣一起翻譯一本講植物的書《植物學》，把 cell 譯成「細胞」：「細」是很小，「胞」是裝著生命的小囊。這個詞傳到日本，成為那裡通用的說法，後來又傳回中國。同一個「胞」字也出現在「同胞」裡——兄弟姊妹，或是自己國家的人，字面上是「從同一個胞出來的」。這樣說來，你那 30 兆個細胞真的是「同胞」：它們是一家人，帶著同一本說明書。
Classroom Activity 1 · 課堂活動一
Onion Skin Under the Microscope 顯微鏡下的洋蔥皮
You need · 準備材料
- A microscope, slides, and cover slips顯微鏡、載玻片和蓋玻片
- A piece of onion一塊洋蔥
- Tweezers and a dropper of water鑷子和一支裝水的滴管
Steps · 步驟
- Break a piece of onion. Peel off the thin, see-through skin between the layers with the tweezers.把洋蔥掰開，用鑷子撕下兩層之間那片薄薄的、透明的皮。
- Lay it flat on a slide in a drop of water and put on the cover slip.把它平放在載玻片上的一滴水裡，蓋上蓋玻片。
- Look at it under low power first. What shapes do you see?先用低倍率觀察。你看到什麼形狀？
- Draw four cells next to each other. Can you find a dot inside each one?畫出相鄰的四個細胞。你能不能在每一個裡面找到一個小點？
Teaching tip: the cells look like rows of bricks, and the dot in each one is the nucleus (a drop of iodine solution, added by the teacher, makes it easier to see). Hooke saw boxes like these in cork more than 350 years ago. If the school has no microscope, many science museums and university websites share photographs of onion cells that the class can draw from.
教學提示：細胞看起來像一排排的磚塊，每一個裡面的小點就是細胞核（由老師滴一滴碘液，會更容易看到）。三百五十多年前，虎克在軟木塞裡看到的就是像這樣的格子。如果學校沒有顯微鏡，很多科學博物館和大學的網站都有洋蔥細胞的照片，可以讓全班照著畫。
Classroom Activity 2 · 課堂活動二
A Cell in a Bag 袋子裡的細胞
You need · 準備材料
- A zip bag, half filled with water or clear hair gel一個夾鏈袋，裝半袋水或透明的髮膠
- A ping-pong ball or a large marble一顆乒乓球或大彈珠
- A handful of dried beans and a piece of yarn一小把乾豆子和一段毛線
Steps · 步驟
- Put the ball into the bag. This is the nucleus.把球放進袋子裡。這是細胞核。
- Add the beans. These are the mitochondria.加進豆子。這些是粒線體。
- Coil up the yarn as small as you can and tape it to the ball. This is the DNA.把毛線盡量捲小，用膠帶貼在球上。這是 DNA。
- Seal the bag. What part of the cell is the bag itself?把袋子封起來。袋子本身是細胞的哪一個部分？
Teaching tip: the bag is the membrane. Let students squeeze it gently: a cell is soft, and its parts drift around. Then pull the yarn out to its full length to show how much longer DNA is than the nucleus that holds it.
教學提示：袋子就是細胞膜。讓學生輕輕捏一捏：細胞是軟的，裡面的零件會漂來漂去。然後把毛線整條拉直，讓學生看到 DNA 比裝著它的細胞核長多少。
⚕ Health note · 健康提醒This lesson is for learning about the body. It is not medical advice. The numbers of cells are scientists' estimates for an adult and are different for every person. Be careful with glass slides and cover slips, and ask an adult before using a microscope.本課是認識身體的教材，不是醫療建議。細胞的數目是科學家對成年人的估計，每個人都不一樣。使用載玻片和蓋玻片要小心，用顯微鏡之前請先問過大人。