One becomes two一個變兩個
Watch the first split. The cell stretches, and then it pinches apart in the middle.
看第一次分裂：細胞拉長，然後從中間斷開。
Living Things · Unit 1 · Lesson 4 · 生命與生態 單元一 第四課
How Are Bacteria and Viruses Different?細菌和病毒哪裡不一樣？
People call both of them germs, and both are far too small to see. But they are not the same kind of thing at all. In a 3D model, watch one bacterium split into two, then four, then thirty-two, all by itself. Then watch a virus, which can do nothing alone, get a living cell to build new viruses for it. Last, find out how many of each would fit across one millimeter.
大家把它們都叫做「病菌」，兩種也都小到看不見。可是它們根本不是同一類東西。在 3D 模型裡，看一個細菌靠自己分裂成兩個、四個，一直到三十二個。再看一個自己什麼都做不了的病毒，怎麼讓一個活的細胞替它做出新的病毒。最後算算看，一毫米的寬度可以排下幾個細菌、幾個病毒。
Big idea · 一句話看懂
A bacterium is a whole living cell. It takes in food, grows, and splits in two by itself. A virus is not a cell. It is a small packet of instructions in a coat, and it is about a hundred times smaller. A virus cannot grow or copy itself. It has to get inside a living cell, and then the cell builds the new viruses. Most bacteria do us no harm, and many are useful.
細菌是一個完整的、活的細胞。它會吸收養分、長大，然後靠自己一分為二。病毒不是細胞，它只是一小包說明書，外面包著一層殼，而且大約比細菌小一百倍。病毒不會長大，也不能複製自己；它必須進到一個活的細胞裡，由那個細胞替它做出新的病毒。大部分的細菌對我們無害，還有很多是有用的。
3D Model · 3D 模型
Two Ways to Multiply 兩種變多的方法
Drag to turn the model, and scroll or pinch to zoom. Start with the bacterium. Press Pause and move the slider slowly. Watch one cell stretch and split, and count how many there are each time. Then choose A virus and move the slider again. This time, look for who is doing the building.
拖曳可以旋轉模型，滾輪或雙指可以縮放。先看細菌。按「暫停」，慢慢拉動滑桿，看一個細胞拉長、斷成兩個，每一次都數一數有幾個。接著選「病毒」，再拉一次滑桿。這一次請注意：動手做的是誰？
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: a bacterium, one whole cell
綠色：細菌，一個完整的細胞 - Yellow loop: the cell's own DNA
黃色的圈：細胞自己的 DNA - Purple: the virus that arrives
紫色：一開始來的那個病毒 - Red curl: the virus's instructions
紅色的小捲：病毒的說明書 - Coral: the new viruses the cell builds
珊瑚色：細胞做出來的新病毒
A teaching model. The sizes are not to scale: a real virus is about one-hundredth the size of a bacterium, far too small to draw beside it. The colors are made up. The virus shown is the kind that infects bacteria. Viruses that infect plants, animals, and people have other shapes and other ways of getting in and out. The 20 minutes is the fastest case for one well-studied bacterium, and the eight new viruses are an example.
這是教學用的模型。大小沒有照比例：真的病毒大約只有細菌的百分之一，小到沒辦法畫在旁邊。顏色是自己配的。這裡畫的是會感染細菌的那一種病毒；感染植物、動物和人的病毒，形狀不一樣，進出細胞的方法也不一樣。「20 分鐘」是一種研究得很清楚的細菌在最快情況下的數字；八個新病毒是舉例。
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
4
Unit 4: How Are Bacteria and Viruses Different?
People often use one word, germs, for both bacteria and viruses. Both are far too small to see, and some of each can make us sick. But they are not two kinds of the same thing. One is a living cell. The other is not a cell at all.
大家常常用「病菌」一個詞，同時指細菌和病毒。兩種都小到看不見，也各有一些會讓我們生病。可是它們並不是同一類東西裡的兩種：一個是活的細胞，另一個根本不是細胞。
A bacterium is one whole cell. It has a wall, a membrane, and its own DNA, though it has no nucleus to keep the DNA in. It takes in food and grows. When it is big enough, it copies its DNA and splits in two. In the best conditions, some bacteria can do this about every 20 minutes.
細菌是一個完整的細胞。它有細胞壁、細胞膜，還有自己的 DNA，只是沒有細胞核來裝 DNA。它吸收養分、長大；長得夠大了，就把 DNA 複製一份，然後一分為二。在最理想的條件下，有些細菌大約每 20 分鐘就能分裂一次。
Bacteria live almost everywhere: in soil, in water, in hot springs, and deep in rock. They live on your skin and inside you too. Your body carries about as many bacterial cells as it has cells of its own. Most of them do no harm, and many are useful. Other bacteria turn milk into yogurt. Only some kinds cause disease.
細菌幾乎到處都有：土壤裡、水裡、溫泉裡，還有很深的岩石裡。你的皮膚上和身體裡面也有。你身上帶著的細菌，數量和你自己的細胞差不多。它們大部分無害，還有很多是有用的。另外有些細菌能把牛奶變成優格。只有一部分種類的細菌會造成疾病。
A virus is much simpler and much smaller. It is a short set of instructions wrapped in a coat of protein. Most viruses are about a hundred times smaller than a bacterium. A virus cannot take in food, and it cannot grow. Left alone, it does nothing at all.
病毒簡單得多，也小得多。它是一小段說明書，外面包著一層蛋白質做的殼。大部分的病毒大約比細菌小一百倍。病毒不會吸收養分，也不會長大。只有它自己的時候，它什麼事也不會做。
To make more viruses, a virus has to get inside a living cell. Once its instructions are in, the cell follows them and builds new viruses out of its own materials. The new viruses then leave and find other cells. There are viruses for every kind of living thing, even for bacteria.
要有更多的病毒，病毒就得進到一個活的細胞裡。它的說明書一進去，細胞就照著做，用自己的材料做出新的病毒。新的病毒再離開，去找別的細胞。每一類生物都有會感染它的病毒，連細菌也有。
So is a virus alive? Scientists do not all agree. It carries instructions and it changes over time, as living things do, but it cannot do anything by itself. The difference matters in medicine. Antibiotics are medicines that stop bacteria from growing or kill them. They do not work on viruses, such as the ones that cause a cold.
那麼病毒算不算活的？科學家的看法並不一致。它帶著說明書，也會像生物一樣隨著時間改變；可是它自己什麼都做不了。這個差別在醫療上很重要。抗生素是抑制細菌生長或殺死細菌的藥，對病毒沒有用；引起感冒的就是病毒。
Read aloud · 課文朗讀
Questions · 閱讀理解
How does a bacterium make more bacteria?
It takes in food and grows. Then it copies its DNA and splits in two.
What is a virus made of?
A short set of instructions wrapped in a coat of protein.
Why can a virus not multiply by itself?
It cannot take in food or grow. It has to get inside a living cell, and the cell builds the new viruses.
Words & Phrases · 生字及片語
germ(n.)病菌People call bacteria and viruses germs.大家把細菌和病毒都叫做病菌。bacteria(n. (pl.))細菌Most bacteria do us no harm.大部分的細菌對我們無害。virus(n.)病毒A virus is much smaller than a cell.病毒比細胞小得多。split(v.)分開；裂開The cell splits in two.細胞一分為二。multiply(v.)增加；繁殖Some bacteria can multiply very quickly.有些細菌可以增加得非常快。harm(n. / v.)傷害These bacteria do no harm.這些細菌沒有害處。yogurt(n.)優格Bacteria turn milk into yogurt.細菌把牛奶變成優格。medicine(n.)藥；醫學The doctor chose the right medicine.醫生選了對的藥。
Quick Check · 小測驗
1. What is a bacterium?
2. How does a bacterium make more bacteria?
3. What does a virus need in order to multiply?
4. Which is smaller?
5. What do antibiotics work on?
How Small? · 到底多小？
How many fit across one millimeter? 一毫米可以排幾個？
One millimeter is the smallest mark on a ruler. Choose a bacterium or a virus, and see how many of them you would have to line up to cross it.
一毫米是尺上最小的一格。選一個細菌或病毒，看看要排幾個才能排滿這一格。
Choose one · 選一個
The line is a stretched scale. Each mark is ten times the one before it. A micrometer (µm) is a thousandth of a millimeter, and a nanometer (nm) is a thousandth of a micrometer.這條線是拉長過的刻度：每一格是前一格的十倍。一微米（µm）是千分之一毫米；一奈米（nm）是千分之一微米。
To cross one millimeter you need · 排滿一毫米需要
in a row, each one across · 個排成一列（每個這麼寬）
Try It in the Model · 在模型裡試試
Four moments to watch 四個值得看的時刻
Compare the two. The bacterium needed nothing but itself. The virus needed a cell, and without one it would have stayed exactly as it was.
比一比這兩個。細菌只靠自己就夠了；病毒需要一個細胞，要是沒有，它就會一直是原來那個樣子。
Thirty-two三十二個
Count the cells. Each one has its own yellow loop of DNA.
數數看有幾個細胞。每一個都有自己的一圈黃色 DNA。
The instructions go in說明書進去了
Find the red curl. That small piece is all the virus needs to send.
找找那個紅色的小捲。病毒要送進去的，就只有這麼一小段。
The cell does the work做事的是細胞
Play it from the start. Where do the new viruses appear, inside the virus or inside the cell?
從頭播放一次。新的病毒是在哪裡出現的——病毒裡面，還是細胞裡面？
Go Further · 延伸閱讀
Your body, and a third tiny helper 你的身體，還有第三種小幫手
The Human Body · Lesson 12 · 人體探索 第十二課How Does Your Body Fight Germs?身體怎麼對抗病菌？See what your body does when a bacterium or a virus gets in.看看細菌或病毒進到身體裡的時候，身體會怎麼做。Go to the lesson · 前往這一課 →How Things Work · Lesson 18 · 萬物原理 第十八課Why Does Bread Rise?麵包為什麼會膨脹？Meet yeast, another living thing that is too small to see.認識酵母——另一種小到看不見的生物。Go to the lesson · 前往這一課 →
Germs by the Numbers · 病菌的數字
Six numbers about bacteria and viruses 六個和細菌、病毒有關的數字
How small, how fast, and how many.
多小、多快、多少。
0.5–5micrometers · 微米
The usual length of a bacterium. A micrometer is a thousandth of a millimeter.細菌一般的長度。一微米是千分之一毫米。
20–300nanometers · 奈米
The width of many round viruses. A nanometer is a thousandth of a micrometer.許多球形病毒的直徑。一奈米是千分之一微米。
1/100the size · 的大小
Most viruses are about one-hundredth the size of most bacteria.大部分的病毒，大約只有大部分細菌的百分之一大。
20minutes · 分鐘
In the best conditions, the bacterium E. coli can split in as little as this.在最理想的條件下，大腸桿菌最快這麼久就能分裂一次。
38trillion · 兆
The estimated number of bacterial cells in and on one human body, about as many as its own cells.一個人身上和體內的細菌細胞，估計有這麼多，和人自己的細胞數量差不多。
1892the year · 年
Dmitri Ivanovsky found the first sign of something smaller than any bacterium that could still spread a disease.伊凡諾夫斯基第一次發現：有一種比任何細菌都小的東西，還是能傳播疾病。
Germ Stories · 病菌的故事
A filter, a mold, a hunter of bacteria, and a common cold 一個濾器、一種黴菌、獵捕細菌的病毒，還有感冒
How people learned that bacteria and viruses are different things.
人們是怎麼知道細菌和病毒是兩回事的。
1892–1898
It went through the filter它穿過了濾器
A disease was spoiling tobacco plants. In 1892, Dmitri Ivanovsky pressed the sap of sick plants through a filter fine enough to hold back bacteria. The filtered sap still made healthy plants sick. In 1898, Martinus Beijerinck repeated the test and showed that the unseen thing multiplied only inside the living cells of the plant. He called it a virus.
有一種病讓菸草一株一株壞掉。1892 年，伊凡諾夫斯基把病株的汁液壓過一種細到能擋住細菌的濾器，結果濾過的汁液還是能讓健康的植物生病。1898 年，貝傑林克重做了這個實驗，並且證明這種看不見的東西只在植物活的細胞裡才會增加。他把它叫做 virus（病毒）。
1928
A mold that stops bacteria一種擋住細菌的黴菌
In 1928, the Scottish doctor Alexander Fleming discovered penicillin, a substance made by a mold. Penicillin kills bacteria by blocking a step in the building of their cell walls. It was the start of the medicines we call antibiotics. A virus has no cell wall and builds nothing by itself, so there is nothing there for such a medicine to block.
1928 年，蘇格蘭醫生弗萊明發現了盤尼西林（青黴素），那是一種黴菌製造的物質。盤尼西林擋住細菌建造細胞壁的其中一個步驟，細菌就活不成。這是我們今天叫做「抗生素」的這類藥的起點。病毒沒有細胞壁，自己也不建造任何東西，所以這種藥在它身上沒有可以擋的地方。
1915
Viruses that hunt bacteria獵捕細菌的病毒
Bacteria get viruses too. In 1915, the British scientist Frederick Twort found a tiny agent that infected and killed bacteria. Such a virus is called a bacteriophage, which means bacteria eater. It lands on a bacterium and injects its instructions, and the bacterium builds new viruses. Bacteriophages are among the most common things in the living world.
細菌也會被病毒感染。1915 年，英國科學家特沃特發現一種會感染並殺死細菌的微小東西。這樣的病毒叫做「噬菌體」，意思是「吃細菌的」。它落在細菌上，把說明書注射進去，細菌就替它做出新的病毒。噬菌體是生物世界裡數量最多的東西之一。
Taiwan · 台灣
A cold is a virus感冒是病毒
Taiwan's Centers for Disease Control explains that the common cold is an infection by viruses, and that the medicines a doctor gives for it treat the fever, the runny nose, and the cough while the body does the rest. It describes antibiotics as substances that stop bacteria from growing or kill them. Which medicine fits an illness is for a doctor to decide.
衛生福利部疾病管制署說明：感冒泛指病毒性感染，醫師開的藥是針對發燒、流鼻水、咳嗽這些症狀，其餘的靠身體自己痊癒。疾管署也說明，抗生素是用來抑制細菌生長或殺死細菌的物質。生什麼病該用什麼藥，要由醫師判斷。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思Bacteria and viruses are the same thing.細菌和病毒是同一種東西。
✓ Fact · 事實A bacterium is a living cell. A virus is a packet of instructions that needs a cell.細菌是活的細胞；病毒是一包說明書，要靠細胞才行。
✗ Myth · 迷思All bacteria are bad for you.細菌都對人有害。
✓ Fact · 事實Most of the bacteria on you and in you do no harm, and many are useful.你身上和體內的細菌大部分無害，還有很多是有用的。
✗ Myth · 迷思Antibiotics work on colds.抗生素可以治感冒。
✓ Fact · 事實Colds are caused by viruses, and antibiotics act on bacteria.感冒是病毒引起的，而抗生素是對付細菌的。
✗ Myth · 迷思Viruses grow and multiply wherever they land.病毒落在哪裡，就在哪裡長大變多。
✓ Fact · 事實A virus cannot grow. It multiplies only inside a living cell.病毒不會長大，而且只能在活的細胞裡增加。
Remember It · 記憶口訣
The difference in a sentence 一句話記住差別
A bacterium is a cell細菌是一個細胞
It eats, grows, and splits in two.
會吃、會長大、會一分為二。
A virus is a packet病毒是一包東西
Instructions in a coat, and nothing more.
一層殼包著說明書，就這樣。
A virus needs a cell病毒需要細胞
The cell builds the new viruses.
新的病毒是細胞做出來的。
A hundred times smaller小一百倍
That is a virus beside a bacterium.
病毒和細菌比起來就是這樣。
Classroom Activity 1 · 課堂活動一
The Doubling Game 加倍遊戲
You need · 準備材料
- A bag of dried beans or small paper squares一袋乾豆子，或一些小紙片
- A sheet of paper, a pencil, and a tray一張紙、一支鉛筆和一個托盤
Steps · 步驟
- Put one bean on the tray. This is one bacterium. Write down 0 minutes and 1.在托盤上放一顆豆子，代表一個細菌。寫下「0 分鐘、1 個」。
- Every bean splits in two. Add a bean for each bean on the tray, and write down 20 minutes and 2.每一顆豆子都一分為二：托盤上有幾顆，就再加幾顆。寫下「20 分鐘、2 個」。
- Keep going, adding 20 minutes each time. How many rounds can you do before you run out of beans?繼續下去，每一次加 20 分鐘。在豆子用完之前，你能做幾輪？
- Work out the number after ten rounds without using beans. How much time has passed?不用豆子，算出第十輪之後的數目。這時候過了多久？
After ten rounds there are 1,024, in 200 minutes. Running out of beans is part of the lesson. Real bacteria run out of food and room in the same way, which is why they cannot keep doubling for long.
十輪之後是 1,024 個，花了 200 分鐘。豆子用完也是這個活動要教的事：真的細菌一樣會把養分和空間用完，所以沒辦法一直加倍下去。
Classroom Activity 2 · 課堂活動二
Cell or Packet? 細胞，還是一包說明書？
You need · 準備材料
- Ten small cards and a pen十張小卡片和一支筆
- Two sheets of paper, one labeled Bacterium and one labeled Virus兩張紙，一張寫「細菌」、一張寫「病毒」
Steps · 步驟
- On each card, write one fact from this lesson, such as “splits in two by itself” or “needs a living cell.”在每張卡片上寫一件這一課學到的事，例如「自己一分為二」或「需要活的細胞」。
- Mix the cards. Take turns drawing one and placing it on the sheet where it belongs.把卡片洗一洗，輪流抽一張，放到它該去的那張紙上。
- Some cards may be true for both, such as “too small to see.” Decide together where to put those.有些卡片可能兩邊都對，例如「小到看不見」。大家一起決定該放在哪裡。
- Then try to explain the difference to someone at home, using only three of the cards.最後只用其中三張卡片，試著把兩者的差別講給家人聽。
A good set of cards covers four questions. Is it a cell? How big is it? How does it make more of itself? Do antibiotics act on it?
一副好的卡片會回答四個問題：它是不是細胞？它有多大？它怎麼變多？抗生素對它有沒有作用？
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）。
- Bacteria are typically 0.5 to 5.0 micrometers in length; their cells do not contain a nucleus; they live in soil, water, acidic hot springs, and the deep crust; most bacteria in and on the body are harmless and many are beneficial, while several species cause disease; penicillin, made by a fungus, kills bacteria by blocking a step in the building of the cell wall細菌一般長 0.5 到 5.0 微米；細胞沒有細胞核；生活在土壤、水、酸性溫泉與地殼深處；人體內外的細菌多數無害、許多有益，少數會致病；黴菌製造的盤尼西林藉由阻斷細胞壁合成的一個步驟來殺死細菌Wikipedia, “Bacteria” ↗
- Under favorable conditions, E. coli takes as little as 20 minutes to reproduce在適合的條件下，大腸桿菌最快 20 分鐘就能繁殖一代Wikipedia, “Escherichia coli” ↗
- The number of bacterial cells in the human body is estimated at around 38 trillion, and the number of human cells at around 30 to 40 trillion人體內的細菌細胞估計約 38 兆個，人類自己的細胞約 30 到 40 兆個Wikipedia, “Human microbiome” ↗
- A virus replicates only inside the living cells of an organism; it consists of genetic material and a protein coat; many spherical viruses are between 20 and 300 nanometers across; most are about one-hundredth the size of most bacteria; viruses infect all life forms, including bacteria; some biologists consider viruses a life form and others do not; Ivanovsky's filter experiment was in 1892, and in 1898 Beijerinck called the filtered infectious substance a virus病毒只能在生物的活細胞內複製；由遺傳物質與蛋白質外殼組成；許多球形病毒直徑 20 到 300 奈米；多數約為多數細菌的百分之一大；病毒感染所有生物，包括細菌；病毒算不算生命，生物學家看法不一；伊凡諾夫斯基 1892 年的過濾實驗；貝傑林克 1898 年把濾過後仍具感染力的物質稱為 virusWikipedia, “Virus” ↗
- In 1898 Beijerinck repeated the filtration experiments and showed that the agent multiplied in the host cells of the tobacco plant貝傑林克 1898 年重做過濾實驗，並證明這種病原能在菸草的宿主細胞內增殖Wikipedia, “Tobacco mosaic virus” ↗
- A bacteriophage is a virus that infects and replicates within bacteria after injecting its genome; Frederick Twort discovered an agent that infected and killed bacteria in 1915; bacteriophages are among the most common entities in the biosphere噬菌體是感染細菌、把基因體注入後在細菌內複製的病毒；特沃特 1915 年發現一種會感染並殺死細菌的病原；噬菌體是生物圈中數量最多的實體之一Wikipedia, “Bacteriophage” ↗
- The stages of the lytic cycle: the phage attaches, injects its DNA, the host builds new phages, and the cell breaks open裂解週期的各階段：噬菌體附著、注入 DNA、宿主合成並組裝新的噬菌體、細胞裂解Wikipedia, “Lytic cycle” ↗
- Penicillin was discovered in 1928 by the Scottish physician Alexander Fleming盤尼西林由蘇格蘭醫師弗萊明於 1928 年發現Wikipedia, “Penicillin” ↗
- Yogurt is a food produced by bacterial fermentation of milk優格是牛奶經細菌發酵製成的食品Wikipedia, “Yogurt” ↗
- Antibiotics do not work for viral illnesses such as the common cold抗生素對感冒這類病毒引起的疾病無效Wikipedia, “Antibiotic” ↗
- Antibiotics are chemical substances used to inhibit the growth of bacteria or to kill bacteria「抗生素」是用來抑制細菌生長或殺死細菌的化學物質衛生福利部疾病管制署〈正確使用抗生素－做自己健康的守護神，以保安康〉 Taiwan Centers for Disease Control ↗
- The common cold refers to viral infections; treatment is mostly for symptoms such as fever, runny nose, and cough, and the body recovers by its own defenses感冒泛指病毒性感染，治療大多以症狀治療為主（發燒、流鼻水、咳嗽），身體會靠自身機制痊癒衛生福利部疾病管制署 澄清專區〈感冒一定要吃藥才會好？〉 Taiwan Centers for Disease Control ↗