What makes a living organism?
An organism can be said to be alive if it:
has defined outer limits or boundaries
takes in free energy, either as sunlight or chemical potential
energy stored in food
excretes waste products, high in entropy
maintains a high level of internal disequilibrium
maintains a constant internal medium, regardless of changing external
conditions.
Characteristics of life forms
The table below compares some of the more commonly
observed characteristics of various kinds of living organisms with those
of a small ecosystem, such as a beehive, and of Gaia. Should not the definition
of life include such larger life forms as these too?
CHARACTERISTIC |
LIFE FORMS
|
|
Bacteria |
Mammal |
Tree |
Beehive |
Gaia |
Reproduction |
+ |
+ |
+ |
- |
- |
Metabolism |
+ |
+ |
+ |
+ |
+ |
Evolution |
+ |
+ |
+ |
+ |
+ |
Thermostasis |
- |
+ |
- |
+ |
+ |
Chemostasis |
+ |
+ |
+ |
- |
+ |
Self-healing |
+ |
+ |
+ |
+ |
+ |
|