What is Life?

If Biology is the study of life, how do we define life?  Is there one characteristic that defines all life?  If you ask a room of students “how can you tell if something is alive” you’ll hear things like “poke it with a stick and see if it moves.”  Unfortunately, that isn’t right.  In fact, there is not one characteristic that defines all life.  Living things are defined by a few characteristics.

All living things:

  • are made up of 1 or more cells.
  • reproduce.
  • are based on a genetic code .
  • grow and develop.
  • obtain and use energy.
  • respond to their environment.
  • maintain a stable internal environment.

Even nonliving things can meet some of these descriptions, so it’s important to be able to tell living from nonliving. For example, a car obtains and uses energy and maintains a stable internal environment.  Some can even respond to their (external) environment!  To be defined as living an object must meet ALL of these requirements.

Technically, viruses don’t meet this description of life and many scientists don’t  consider them to be living things.  However, since they act like living things, they are studied under the umbrella of biology in a field either specifically called Virology or as a broader biology field called Microbiology.

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