All cells have three things in common

所有的細胞都有三個共通點，不管它們是什麼類型的細胞。

no matter what type of cell they are.

所有細胞具有細胞膜，它能把細胞的內部和環境分開。

All cells have a cell membrane which separates the inside the cell from its environment,

細胞質是一種果凍狀流體，DNA是細胞的遺傳物質。

cytoplasm, which is a jelly-like fluid,

細胞可分為兩大類。

and DNA which is the cell's genetic material.

第一類是真核細胞。

There are two broad categories of cells.

它們具有許多細胞器，包括細胞核和其他特殊部位。

The first category is eukaryotic cells.

真核細胞是屬於較先進及複雜的細胞，如植物和動物中的細胞。

They have organelles

第二類是原核細胞。

which include the nucleus and other special parts.

它們不具有細胞核或膜封閉的細胞器。

Eukaryotic cells are more advanced, complex cells

他們仍是有遺傳物質，但它不在細胞核內。

such as those found in plants and animals.

原核細胞通常是單細胞的生物，例如細菌。

The second category is prokaryotic cells.

那麼，什麼是細胞器？

They don't have a nucleus or membrane enclosed organelles.

細胞器意思是「小器官」。

They do have genetic material but it's not contained within a nucleus.

細胞器是細胞中能執行特殊作業的小器官。

Prokaryotic cells are always one celled,

讓我們先從細胞核介紹，它是細胞的控制中心。

or unicellular organisms, such as bacteria.

細胞核含有DNA或遺傳物質。

So what are organelles?

DNA決定細胞要做的事情，以及如何去做。

Organelle means "little organ."

染色質是在細胞核的內部那些攤開又糾結在一起的DNA。

Organelles are the specialized parts of a cell that have unique jobs to perform.

當細胞準備分裂，DNA會自動濃縮成為染色體。

Let's start with the nucleus, the control center of the cell.

細胞核中還包含一個細胞核仁，這結構是用來製作核糖體的。

The nucleus contains DNA or genetic material.

當核糖體離開細胞核後，它們會執行合成或製造蛋白質等重要工作。

DNA dictates what the cell is going to do

在細胞核外面，核糖體和各種細胞器漂浮在細胞質中，

and how it's going to do it.

細胞質就像是一種果凍狀的物質。

Chromatin the tangled, spread out form of DNA found inside the nuclear membrane.

核糖體會在細胞質內自由遊走，

When a cell is ready to divide

或附加到內質網上，可縮寫為“ER”。

DNA condenses into structures known as chromosomes.

總共有兩種類型的ER：

The nucleus also contains a nucleolus,

粗糙內質網上附著了核糖體，

which is a structure where ribosomes are made.

平滑內質網上沒有附著核糖體。

After ribosomes leave the nucleus

內質網是用來輸送材料的封閉細胞膜通道，

they will have the important job of "synthesizing",

可輸送的材料例如由核糖體合成的蛋白質。

or making, proteins.

蛋白質和其他物質被放在小泡內並透過內質網傳遞

Outside the nucleus the ribosomes and the rest of the organelles

最後是由高爾基體接收它們。

float around in cytoplasm, which is the jelly-like substance.

當蛋白質通過高爾基體，它們被定制成該細胞可以使用的形式。

Ribosomes may wander freely within the cytoplasm

高爾基體將通過的蛋白質轉化折疊為可用的形狀

or attach to the endoplasmic reticulum, sometimes abbreviated as ER.

或添加其他材料到它們，如脂類或碳水化合物。

There are two types of ER:

空泡是存儲不同材料網狀結構。

rough ER has ribosomes attached to it

在植物細胞中，液泡儲存水。

and smooth ER doesn't have ribosomes attached to it.

再回到動物細胞，你會看到一個名為溶酶體細胞器。

The endoplasmic reticulum

溶酶體是損壞或磨損細胞零件的垃圾收集器。

is a membrane enclosed passageway for transporting materials

他們充滿了能打破細胞碎片的酶。

such as the proteins synthesized by ribosomes.

線粒體是動物和植物細胞中的能量廠房。

Proteins and other materials

在呼吸作用過程中，

emerge from the endoplasmic reticulum

線粒體產生ATP分子，能對於所有的細胞活動提供能量。

in small vesicles

需要更多能量的細胞具有更​​多的線粒體。

where the Golgi apparatus, sometimes called the Golgi body

同時，細胞透過細胞骨架保持其形狀。

receives them.

細胞骨架包括細小的微絲，

As proteins move through the Golgi body they're customized

其由蛋白質，微管所組成的。微管是很薄的中空管。

into forms that the cell can use.

一些生物體如植物，是光自養生物

The Golgi body does this by folding the proteins into usable shapes.

他們吸收陽光的能源

or adding other materials on to them

細胞內有稱為葉綠體的細胞器。

such as lipids

光合作用就在葉綠體發生的。

or carbohydrates

它呈現綠色的，因為它有一個綠色的葉綠素。

Vacuoles are sac-like structures that store different materials.

植物細胞在細胞膜的外面，有支持和保護功能的細胞壁。

Here, in this plant cell, the central vacuole stores water.

動物細胞則是沒有細胞壁。

Going back to the animal cell,

有些細胞有獨特的結構。這裡僅僅介紹少數。

you'll see an organelle called a lysosome.

例如在人類中，呼吸道上有具有纖毛的細胞。

Lysosomes are the garbage collectors

這些是微小髮狀凸起物，可以像波浪地移動。

that take in damaged or worn out cell parts.

此功能可幫助抓住由空氣吸入的顆粒，當咳嗽時就能將其驅逐出去。

They are filled with enzymes that break down this cellular debris.

某些細胞中的特點是鞭毛。

The mitochondrion in is an organelle that is the powerhouse for both

某些細菌有鞭毛。

animal and plant cells.

鞭毛就像一個小尾巴，可以幫助細胞移動或推動。

During a process called cellular respiration

人類細胞中惟一具有鞭毛的是精子。

the mitochondria make ATP molecules

總之，請記住：

that provide the energy for all the cells activities.

真核細胞包括植物和動物細胞，具有細胞核和膜封的細胞器，

Cells that need more energy

而原核細胞是單細胞生物，沒有這些東西。

have more mitochondria.

所有細胞具有細胞膜，細胞質和遺傳物質。

Meanwhile the cell maintains its shape

僅植物細胞具有葉綠體，植物和動物細胞具有線粒體。

through a cytoskeleton.

The cytoskeleton includes the thread-like microfilaments

which are made of protein

and microtubules which are thin hollow tubes

Some organisms

such as plans that are photoautotrophic

meaning they capture sunlight for energy

have cells with an organelle called a chloroplast.

The chloroplast is where photosynthesis happens

It's green because it has a green pigment called

chlorophyll.

Plant cells also have a cell wall outside of their cell membranes

that shape, support, and protect the plant cell.

Animal cells never have a cell wall

There are many other unique structures that only some cells have.

Here are just a few.

In humans, for example, the respiratory tract is lined with cells that have cilia.

These are microscopic hair-like projections

that can move in waves.

This feature helps trap inhaled particles in the air and expels them when you cough.

Another unique feature in some cells is flagella.

Some bacteria have flagella.

A flagellum is like a little tail that can help a cell move or propel itself.

The only human cell that has a flagellum

is a sperm cell.

In summary remember:

eukaryotic cells are plant and animal cells with a nucleus and membrane-enclosed organelles

While prokaryotic cells are unicellular organisms without these things.

All cells have a cell membrane, cytoplasm and genetic material.

And even though only plant cells have chloroplasts

both plant and animal cells have mitochondria.