Like whole individuals, cells have a life span. During their life cycle (cell cycle), cell size, shape, and metabolic activities can change dramatically. A cell is “born” as a twin when its mother cell divides, ① producing two daughter cells. Each daughter cell is smaller than the mother cell, and except for unusual cases, each grows until it becomes as large as the mother cell ② was. During this time, the cell absorbs water, sugars, amino acids, and other nutrients and assembles them into new, living protoplasm. After the cell has grown to the proper size, its metabolism shifts as it either prepares to divide or matures and ③ differentiates into a specialized cell. Both growth and development require a complex and dynamic set of interactions involving all cell parts. ④ What cell metabolism and structure should be complex would not be surprising, but actually, they are rather simple and logical. Even the most complex cell has only a small number of parts, each ⑤ responsible for a distinct, well-defined aspect of cell life.

* metabolic: 물질대사의 ** protoplasm: 원형질