In order to maintain life an organism must exhibit:
The ability to convert food into energy this includes converting the energy stored in the bonds of Glucose into the high energy storage compound ATP. This usually occurs in the mitochondria.
The ability to maintain a stable internal environment(maintain homeostasis) Humans use the nervous and endocrine system to do this.
The ability to produce more of their own kind (not needed for the individual organism to survive) it can be sexual or asexual.
The ability to increase in size.
The ability to remove metabolic wastes wastes that are made during chemical reactions in the body (Carbon Dioxide,Water, & Urea)
The ability to obtain and process food (Autotrophic or Heterotrophic)
The ability to move materials into, out of and throughout an organism
The ability to manufacture materials not able to be aquired from the environment. We synthesize many enzymes and hormones.
A space ship lands at your house. You look inside and see a creature. Describe what would you do to see if the alien was alive. Be specific... and also state which life function you are testing to see that the organism exhibits. Example: You offer it food...nutrition