Cellular Level -- 細胞層次

Although there are many different kinds of cells in the human body, most of them contain a nucleus, a thick liquid called cytoplasm, and enclosed by a very thin layer of cell membrane.

雖然人體內有很多種類的細胞，但大部分都包含著一個細胞核（nucleus）、一種名叫細胞間質（cytoplasm）的濃厚液體，並且由一層薄薄的細胞膜（cell membrane）包裹著。

Nucleus

The nucleus is the control center of a cell. It contains DNA (deoxyribonucleic acid) molecules, which house the cell's chemical information. A DNA molecule is composed of millions of atoms, structured in a double helix shape. Before a cell divides, its DNA molecules replicate (i.e., copy themselves), to make sure that a complete set of information can be passed to each new cell.

細胞核（Nucleus）

細胞核是一個細胞的控制中心，它藏著帶有細胞之化學訊息的 DNA（去氧核糖核酸）分子，DNA 是一個呈雙螺旋狀的分子，由數以百萬計的原子組成。一個細胞在分裂之前，其 DNA分子會先自身複製，以確保整套訊息能夠被傳達至每一個新的細胞。

The nuclear membrane separates the nucleus from the other components of the cell. However, the nuclear membrane contains numerous holes called nuclear pores, which allow chemical contact between the nucleus and the surroundings.

細胞核膜把細胞核與細胞的其餘部分分隔起來，不過，細胞核膜上存在著很多小孔，容許細胞核與外界作化學上的接觸。

Cytoplasm

The cytoplasm is a transparent, jelly-like fluid that contains up to 90% water. It houses the organelles--some structures with special functions inside the cell. The number and types of organelles depend on the functions of the cell.

細胞間質（Cytoplasm）

細胞間質是一種透明、魚膠狀的液體，約有90%為水分，裡面藏著細胞器（organelles）──細胞內一些具有其特殊工能的結構。細胞器的數目和種類則視乎該細胞的工能而定。

A typical cell usually includes the following organelles:

一個典型的細胞通常包括以下的細胞器：

Endoplasmic Reticulum
The endoplasmic reticulum is a highly folded system responsible for making and storing proteins and fats.

內質網（Endoplasmic Reticulum）
內質網是一個由膜摺疊而成的系統，負責製造及儲存蛋白質和脂肪等物質。

Ribosomes
Although ribosomes are very small in size, they are usually numerous in number, and can scatter among the cytoplasm or attach to the endoplasmic reticulum. It is important for the synthesis of protein in the cell.

核糖體（Ribosomes）
雖然核糖體的體積最為細小，但它們在一個細胞中往往卻是為數眾多的一群，而且可以分散在細胞間質之中或依附在內質網上，對蛋白質的合成有重大作用。

Golgi Body
Golgi body is made up of membranes that store and release the substances produced by the cell. Besides, it also makes lysosome.

高氏體（Golgi Body）
高氏體是由儲存及釋放細胞所製造物質的膜構成。此外，它亦會製造溶酶體。

Lysosome
Lysosome is a reservoir that contains digestive enzymes. These kind of enzymes can break down worn-out organelles and digest foreign substances. During the early stages of development, lysosomes even destroy the cell that surrounds them. This is called "self-digestion" or autolysis.

溶酶體（Lysosome）
溶酶體是一個具有消化能力化學物的儲存庫，這些化學物能分解損耗了的細胞器和消化外來的物質。在發展的初期，溶酶體甚至會摧毀覆蓋著它們的細胞──“自我消化”或自體溶解。

Mitochondrion
Mitochondrion (plural: mitochondria) is an oval shape structure with a heavily folded inner membrane (i.e., cristae). This is where aerobic respiration takes place and energy is released. Mitochondria are often called the energy warehouse of the cell.

粒線體（Mitochondrion）
粒線體呈卵狀，內膜高度摺疊成嵴，有氧呼吸就是在此進行，從而釋放能量。粒線體經常被喻為細胞內的能源儲存庫。

Cell Membrane

Cell membrane is formed by two layers of phospholipid molecules. They act as a protective shield, allowing some substances to pass through, but preventing the passage of others at the same time.

細胞膜（Cell Membrane）

細胞膜是由兩層的磷脂分子組成，它彷如一個防護罩，容許某些分子進入的同時，卻阻止了其他分子的進入。

Cell Division

細胞分裂

有絲分裂
Mitosis

減數分裂
Meiosis

About 50 millions cells die in a second in the human body. At the same time, they are replaced by the same number of new cells. The life cycle of cells varies from one kind to another. For example, cells lining the skin and the alimentary canal have to experience a lot of wear and tear, and are almost replaced every 24 hours. On the contrary, highly specialized cells such as the neurons (i.e., nerve cells) do not divide at all once they have been formed.

人體內每秒鐘約有五千萬個細胞會死去，並同時由另外五千萬個新生細胞所取代。細胞的生命週期按其種類的不同而有所分別。例如，位於皮膚表面和消化道上的細胞，差不多每隔廿四小時便會被取替。反觀那些極為專門的細胞，如神經元（神經細胞），當發展完成後便會失去繁殖的能力。

Cell division is the process by which cells reproduce. There are two types of cell division: mitosis and meiosis.

細胞分裂是細胞繁殖的過程，可透過兩種形式進行：有絲分裂和減數分裂。

Mitosis is the division of a cell nucleus to produce two identical cells. It is the process that the body uses for growth and repair.

有絲分裂（mitosis）指由一個細胞分裂成兩個完全相同的細胞，它是人體生長和修復的程序。

Meiosis occurs in the reproductive system to produce sex cells. It actually involves two cell divisions, one after the other, to produce four new cells that are genetically unique.

減數分裂（meiosis）在生殖系統內進行以產生性細胞，它實際上是經過前後兩次分裂後產生四個在遺存特質上是獨一無二的細胞。

When cell division becomes uncontrolled, it may lead to growths called tumors, which often spread out rapidly, and even interfere with normal body functioning. Scientists believe that certain carcinogens, accidental rearrangement of DNA molecules in a cell, and virus infection can all be factors that trigger the action of cancers.

當細胞分裂變成失控的時候，就會引致腫瘤的出現，而且通常會很快地擴展開去，影響到人體的正常運作。科學家相信一些致癌物質、細胞內 DNA 分子意外地重新排列和過濾性病毒感染等，都會觸發癌症的發生。