life form vs organism

life form

noun
  • The morphology of an organism that distinguishes it from others. 

organism

noun
  • Something with many separate interdependent parts, seen as being like a living thing; an organic system. 

  • A discrete and complete living thing, such as animal, plant, fungus or microorganism. 

How often have the words life form and organism occurred in a corpus of books? (source: Google Ngram Viewer )