Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Definition of life
Name: Chris E Lee
Age: N/A
Location: N/A
Country: N/A
Date: N/A 


Question:
Does anyone know what is currently the most accepted idea on the characteristics needed for any kind of life?



Replies:
I assume since no one has answered your question in nearly a month that no one has a sufficient answer for you, so I'll take a crack at it. As far as I know, most of the accepted criteria for determining whether something is "alive" can also, at least individually, be applied to non-living things -- it's kind of difficult to say. The main points I can think of at the moment are:

MOTION -- does it seem to move under its own power? Does it move with some discernible purpose? (Toward food, away from heat, etc)

REPRODUCTION -- does it have some way of making more of itself, either through sexual reproduction or by budding or fissioning in some way?

CONSUMPTION -- does it eat or drink? Does it take in nutrients in one way or another in order to survive, grow, and eventually multiply?

GROWTH -- does the organism develop over time, increase in complexity, until it reaches a mature stage?

STIMULUS RESPONSE -- does the organism respond to external stimuli, i.e. has a nervous system of some sort to detect external conditions?
To qualify as a living thing, an organism must in one way or another meet each of those criteria. After all, crystals grow in solution, and take on more material from the surrounding solution in order to do so, but do not respond neurologically if you poke them with a pin. Of course, you don't often see mature Ponderosa pines strolling down Fifth Avenue either, so the criteria are open to interpretation. Plants move through growth, except in special cases like the Venus flytrap; most plants follow the sun through a complex system which floods the side of the plant shaded from the sun with water, swelling the shaded side and causing the plant to lean toward the sun.

Even when all the criteria are met, it may be difficult to determine if something is alive or not. Take a virus. It is a strand of either DNA or RNA, and cannot move on its own power. Yet when it attaches itself to a receptive host, it inserts itself into the cell and forces the host to make more of the virus, a clear reproductive plan. It utilizes the host's cellular processes to do so, in a sense taking in "nutrients" in order to survive and multiply. In some cases, exterior conditions cause the virus to integrate itself into the host DNA, in order to hide until conditions are better to reproduce, showing a response to external stimuli. Is it alive? Please read more about this at your local library.

Wordsworth



Click here to return to the Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory