The cold virus is sucked inside your lungs and lands on a cell on your airway lining.

感冒病毒就這樣被吸入你的肺裡，並在呼吸道裡的細胞上著陸。

Every living thing on Earth is made of cells, from the smallest one-celled bacteria, to the giant blue whale, to you.

地球上所有生物都是由細胞組成的，從最小的單細胞菌，到巨大的藍鯨然後到你。

Each cell in your body is surrounded by a cell membrane, a thick flexible layer made of fats and proteins, that surrounds and protects the inner components.

你身體裡每個細胞都有細胞膜，細胞膜是由一層又厚又富有彈性的脂肪和蛋白質組成，圍繞並保護內部的細胞。

It's semipermeable, meaning that it lets some things pass in and out but blocks others.

它是半滲透性的，意味著它可以讓某些東西進出，但會阻止某些東西進入。

The cell membrane is covered with tiny projections.

細胞膜上覆蓋著微小的突起物。

They all have functions, like helping cells adhere to their neighbors or binding to nutrients the cell will need.

它們每個都具有功能，例如幫助細胞附著在它的鄰居上，或和細胞需要的營養結合。

Animal and plant cells have cell membranes.

動物和植物細胞都具有細胞膜。

Only plant cells have a cell wall, which is made of rigid cellulose that gives the plant structure.

但只有植物細胞有細胞壁，它是由硬質纖維素組成，能形成植物的支撐架構。

The virus that was sneezed into your lungs is sneaky.

經由噴嚏進入肺內的病毒細胞很狡猾，

Pretending to be a friend, it attaches to a projection on the cell membrane, and the cell brings it through the cell membrane and inside.

它假裝成朋友，附著在細胞膜的某個突起上，這個細胞就帶著它穿過細胞膜到內部，

When the virus gets through, the cell recognizes its mistake.

當病毒順利通過，細胞辨認出錯誤。

An enemy is inside!

敵人在裡面！

Special enzymes arrive at the scene and chop the virus to pieces.

特種酵素抵達現場，把病毒大卸八塊，

They then send one of the pieces back through the cell membrane, where the cell displays it to warn neighboring cells about the invader.

然後把其中一塊送回去，通過細胞膜，細胞在膜上將其示眾 以警告鄰近細胞有入侵者。

A nearby cell sees the warning and immediately goes into action.

鄰近的細胞看見警告，立刻做出行動，

It needs to make antibodies, proteins that will attack and kill the invading virus.

它需要製造抗生素，它是蛋白質成分，會攻擊並殺掉入侵的病毒。

This process starts in the nucleus.

這個過程在細胞核內開始，

The nucleus contains our DNA, the blueprint that tells our cells how to make everything our bodies need to function.

細胞核含有我們的去氧核糖核酸 (DNA) ，為一張藍圖，告訴我們的細胞如何製造身體所需的東西，以發揮功能。

A certain section of our DNA contains instructions that tell our cells how to make antibodies.

去氧核糖核酸的某段包含指令，告訴我們的細胞如何製造抗生素。

Enzymes in the nucleus find the right section of DNA, then create a copy of these instructions, called messenger RNA.

在核內的酵素會找到正確的那一段去氧核糖核酸，然後複製這些指令，稱做傳訊核醣核酸 (mRNA)。

The messenger RNA leaves the nucleus to carry out its orders.

傳訊核醣核酸離開細胞核去執行指令，

The messenger RNA travels to a ribosome.

傳訊核醣核酸前往核醣體，

There can be as many as 10 million ribosomes in a human cell, all studded along a ribbon-like structure called the endoplasmic reticulum.

人體細胞內有可高達一千萬個核醣體，像釘子般綴滿一條帶狀結構，稱為內質網。

This ribosome reads the instructions from the nucleus.

這個核醣體讀取從細胞核傳來的指令，

It takes amino acids and links them together one by one, creating an antibody protein that will go fight the virus.

它需要胺基酸並一個個串起來，製造出抗生素蛋白質去對抗病毒。

But before it can do that, the antibody needs to leave the cell.

但是在此之前，抗生素需要離開細胞。

The antibody heads to the golgi apparatus.

抗生素前往高基氏體，

Here, it's packed up for delivery outside the cell.

在這裡抗生素包裹起來，準備運送到細胞外，

Enclosed in a bubble made of the same material as the cell membrane, the golgi apparatus also gives the antibody directions, telling it how to get to the edge of the cell.

包在一個跟細胞膜同樣材料所製的泡泡裡，高基氏體也給抗生素方向，告訴它如何走到細胞的邊緣。

When it gets there, the bubble surrounding the antibody fuses to the cell membrane.

當它到達那裡，這個包圍著抗生素的泡泡會與細胞膜融合，

The cell ejects the antibody, and it heads out to track down the virus.

細胞排出抗生素，而它出發向外去追捕病毒，

The leftover bubble will be broken down by the cell's lysosomes and its pieces recycled over and over again.

留下來的泡泡會分解由細胞的溶酶體執行，溶掉的碎片會不斷回收利用。

Where did the cell get the energy to do all this?

細胞從何處得到能量執行這些事？

That's the roll of the mitochondria.

那就是粒線體的角色了。

To make energy, the mitochondria takes oxygen - this is the only reason we breathe it - and adds electrons from the food we eat to make water molecules.

要產生能量，粒線體需要利用氧氣，這是我們吸進氧氣的唯一理由，並從我們所吃的食物中加進電子，以製造水分子。

That process also creates a high energy molecule, called ATP, which the cell uses to power all of its parts.

那個過程也產生一種高能量分子，稱為三磷酸腺苷，細胞用它提供能量給所有的零件。

Plant cells make energy a different way.

植物細胞以不同的方法產生能量，

They have chloroplasts that combine carbon dioxide and water with light energy from the sun to create oxygen and sugar, a form of chemical energy.

它們有葉綠體，能結合二氧化碳及水，藉助從太陽得來的光能產生氧氣及糖，為化學能的一種形式。

All the parts of a cell have to work together to keep things running smoothly, and all the cells of your body have to work together to keep you running smoothly.

細胞內的所有零件都必須合作，讓一切運作順利，你身體的所有細胞也都必須合作，讓你運作順利。

That's a whole lot of cells.

那是一大堆的細胞。

Scientists think there are about 37 trillion of them.

科學家認為大約有 37 兆個！