Expert: John Locke - 8/4/2007

Question
Hi! I would like to know why cell is called the functional unit of life? I searched elsewhere but couldn't find a satisfying answer. Could you help me?

Answer
Thanks for using AllExperts, Anjali.

Cells are referred to as the functional unit of life for a very practical reason: so far as we are aware, a cell is the smallest creature that carries on all the functions of life. All organisms are made of cells--from the relatively complex mammals to amoebas and bacteria--and all life functions are ultimately controlled by cells. Thus, cells control themselves (this is how bacteria and other single-celled organisms survive), and by working together, they can accomplish complex tasks that they could not individually (this is how all multi-celled organisms survive). It is in this sense that cells are termed the functional unit of life--cells are themselves alive, and are also the "building blocks" of more complex life.

Let's take a step back for a moment. The field of biology recognizes certain characteristics that all living organisms possess in one way or another (for instance, organisms can adapt to their environment, use energy, and reproduce). To be called "life," a creature must possess those attributes: if it does not, it cannot be said to have life. There's no universal agreement as to what exactly should be on that list, though by any definition promoted thus far, cells fulfill all the requirements of life.

For more information, let me recommend this site about scientific considerations used in defining life. It's a scan of a journal article published in Science Reporter, an Indian popular science journal:

http://www.scribd.com/doc/1016/Life-from-birth-to-death/

Also, here's a resource on the characteristics of cells. Read chapter one for a list of traits that all living organisms possess:

http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4

Enjoy!