正文阅读
Cells and how to run them
神奇的细胞如何运行
The chemical reactions on which life depends need a place to happen. That place is the cell. All the things which biology recognises as indisputably alive are either cells or conglomerations of cells (viruses fall into disputable territory). Since the middle of the 19th century the cell has been seen as the basic unit of life.
生命赖以生存的化学反应需要一个发生地。那个地方就是细胞。所有生物学认为无可争议的活物不是细胞就是细胞聚合体（病毒属于有争议的领域）。自19世纪中叶以来，细胞一直被视为生命的基本单位。
A cell requires something to keep its insides in and the outside out. That is the role of the cell membrane, a flexible film made largely of lipids. These are smallish tadpole-shaped molecules with heads that are comfortable in water and twin tails that shun it. When put into a watery solution they naturally form double layers in which the water-tolerant heads are on the outside and the water-wary bits on the inside. Some plant, fungal and bacterial cells employ more rigid structures, called cell walls, as further fortifications beyond their membranes. But it is the membrane which defines the cell.
细胞需要一些东西来保持其内部和外部。细胞膜就发挥了这样的作用，它是一种主要由脂质构成的柔性膜。它们是蝌蚪状的小分子，头部亲水，双尾疏水。当放入水溶液时，它们会自然形成双层结构，其中耐水的头部在外面，疏水的部分在里面。一些植物、真菌和细菌细胞有更坚硬的结构，称为细胞壁，作为细胞膜之外的进一步防御结构。但是是膜决定了细胞。
What is more, the disposition of membranes determines what sort of cell it is. Some creatures use membranes chiefly to define their perimeters. These are called prokaryotes, and come in two varieties, bacteria and archaea. In others they are also used to create structures within cells, notably a nucleus to contain the dna on which genes are written. Such cells may have ten or 20 times more membrane within them than they have defining their surfaces. They are called eukaryotic, Greek for truly nucleated. Creatures made from them are eukaryotes.
而且，细胞膜的位置决定了它是什么类型的细胞。有些生物主要用膜来确定它们的周长。它们被称为原核生物，分为两种：细菌和古菌。在另一些细胞中，膜也被用来创造细胞内结构，特别是一个包含基因的DNA的细胞核。这些细胞内的膜可能比它们表面的膜多10到20倍。它们被称为真核生物，在希腊语中的意思是真正有核的。由它们组成的生物是真核生物。
/3 
