“You are probably taller now than you were 4 years ago. What, specifically, caused you to become taller? Explain what happened on a cellular level.”

The cell is the basic unit of life.  Anything smaller than a cell; unable to perform the jobs of the cell, is not a form of life.  Cells are what larger organisms are made of.  Having the ability to understand life on a cellular level allows us to understand the larger organisms.

In terms of human growth, what happens on a cellular level?  Over a time period of, in this case, 4 years, what happens inside a child’s body that causes them to grow taller?  Cells themselves do not grow beyond a certain point, as they would get so large that the systems inside the cell would no longer function properly.  Think of an infant, if they had the same cells from infancy to adulthood, and the cells just grew, the cells would be incredibly large and unable to function properly.  What happens?  The cells actually duplicate.  The cells split, through a process called mitosis, which creates a genetically identical cell.

There are two different phases of the cell cycle, the mitotic phase which is where mitosis occurs, and the inter-phase, during the times when the cell is just carrying out the job it is designed to do.  The cells know what phase to be in because they receive messages from other cells.  The outer membrane of the cell is covered with receptors, that receive messages that “tell” the receiving cell about other cell activity, and this tells the cell what phase it should be in.  The cells in an organism work together systematically to carry out growth, healing, and many other purposes of the organism.