地球上生存着数百万种生物,从微小的细菌,到枝叶繁茂的高大树木,丰姿多采,形态万千。它们虽然千差万别,但其内部构造却都是由一种基本单位——细胞构成的。最简单的生物,如细菌只有一个细胞,而高等动植物却有无法计数的细胞组成的。这些细胞就是生命活动的基本单位。一、细胞的组成与功能细胞通常很小,直径只有10～16微米(μ,1毫米=1,000微米),小的甚至只有0.2～5微米。不借助显微镜是无法看见它们。细胞的形状也是多种多 There are millions of species living on the planet, from tiny bacteria to lush, tall trees that have a variety of forms and shapes. Although they vary widely, their internal structures are made up of one basic unit, the cell. The simplest creatures, such as bacteria, have only one cell, while higher animals and plants have cells that can not be counted. These cells are the basic unit of life activity. First, the cell composition and function of cells is usually small, only 10 to 16 microns in diameter (μ, 1 mm = 1,000 microns), small or even only 0.2 to 5 microns. They can not be seen without a microscope. The shape of the cell is also varied