"What is an organism?"
Perhaps in trying to answer the question, "what is an organism?", we encounter the same problem we do in trying to answer the question, "what is life?". With the latter question, we really want to know about the nature of an activity, namely the activity of living. Perhaps with the former question, we also really want to know about the nature of an activity, but we have no verb-form to substitute for "organism". Therein might lie the problem. We might solve it by coining a verb: 'organisimizing' [OR--guh-NIHZ-ih-MY-zing], from 'to organisimize'. It seems a mouthful, yet so do 'systematizing' and 'operationalizing'. We familiarize ourselves to a new word after a while (aside: as we did with Citizendium).
What characterizes 'organisimizing'? I would answer: the activity of working together as a living collection of observable interrelated units of provisionally ignorable internal structure. That answer applies to the behavior of single cells, the internal structure of whose constituents we can provisionally ignore, but it generalizes to the behavior of any collection of cells that satisfies the criteria of living from the perspectives of open system nonequilibrium thermodynamics, information processing, self-reproduction and evolution, self-organization, and autonomous functioning in its own behalf. To organisimize means to form a living community of some kind that allows of interpretable description (i.e., modeling).
If the suggestion of neologizing the activity of organisms to better understand organisms seems unconventional or radical, we might take heart from Goldenfeld and Woese, who reminded us of the father of chemistry, Antoine Lavoisier’s words:
We cannot improve the language of any science without at the same time improving the science itself; neither can we, on the other hand, improve a science without improving the language or nomenclature which belongs to it.
- I. Simple uses.
- 1. Organic structure; = ORGANICITY n. Obs. rare. (1701, 1706, 1890) 
- 2. a. A whole with interdependent parts, compared to a living being; an organic system. (1768, 1860, 1900, 1993) 
- b. Philos. The theory that in science everything is ultimately an organic part of an integrated whole. (1925, 1928, 1959, 1965) 
- 3. a. An individual animal, plant, or single-celled life form. Also: the material structure of such an individual; an instance of this. (1834, 1842, 1858, 1882, 1894, 1924, 1976, 1984) 
- b. Organized existence as a whole. rare. (1887, 1996) 
- II. Compounds.
- 4. organism-environment a., of, relating to, or designating the relationship between an organism and its environment. (1946, 1958, 2003) 
- organismal a., of, relating to, or concerned with an organism or organisms. (1861, 1940, 2003) 
- Goldenfeld,N.; Woese,C. (2007) Biology's next revolution. Nature 445:369 Link to Full-Text
- 1701 N. GREW Cosmol. Sacra II. iii. §11 It is the advantagious Organism of the Eye, by which that is procured. 1706 J. EVELYN Sylva 353 So astonishing and wonderful is the organism, parts and functions of plants and trees. 1890 J. MARTINEAU Seat Authority Relig. II. ii. §3. 245 From the complexion of the language and the organism of the style.
- 1768 A. TUCKER Light of Nature II. II. xxiii. 277 When an artist has finished a fiddle to give all the notes in the gamut, but not without a hand to play upon it, this is an organism. 1860 J. L. MOTLEY Hist. Netherlands (1868) I. vi. 299 The weight of the strong Protestant organism..might have balanced the great Catholic League. 1900 J. D. ROBERTSON Holy Spirit iii. 53 Paul first taught us to speak of society as an organism. 1993 N.Y. Times Mag. 22 Aug. 44/3 A burbland created almost all at once, very fast and virtually ex nihilo, right after the war, a self-contained social organism.
- 1925 A. N. WHITEHEAD Sci. & Mod. World (1926) 112 This doctrine involves the abandonment of the traditional scientific materialism, and the substitution of an alternative doctrine of organism. 1928 Jrnl. Philos. Stud. 3 33 He [sc. Lloyd Morgan] saw no reason why the term organism should not be applied to all those ‘natural entities’, as he called them, existing throughout the universe in emergent degrees of complexity. 1959 A. W. LEVI Philos. & Mod. World xii. 486 The ‘philosophy of organism’..suggests the synthesis of incompatibles. 1965 E. E. HARRIS Found. of Metaphys. in Sci. xiv. 282 The appropriate philosophy for contemporary science must be..a philosophy of organism.
- 1834 Philos. Trans. Royal Soc. 124 359 The introduction of new powers into an organism necessarily requires a modification in its mode of development. 1842 H. MILLER Old Red Sandstone (ed. 2) i. 40 There are formations which yield their organisms slowly to the discoverer. 1858 G. H. LEWES Sea-side Stud. 157 The simplest organisms breathe, exhale, secrete, absorb, and reproduce by their envelopes alone. 1882 A. W. WARD Dickens vii. 205 A mental and moral vigour supported by a splendid physical organism. 1894 H. NISBET Bush Girl's Rom. 60 Wounded and insulted in the most sensitive part of his organism. 1924 C. MACKENZIE Old Men of Sea viii. 116 His was a cruel paralysis by which one complete half of his organism had been affected. 1976 P. PARISH Medicines (1982) I. i. 18 The most obvious example is the cure of disease by drugs such as antibiotics, which destroy the invading organisms that were making the patient ill. 1984 J. F. LAMB et al. Essent. Physiol. (ed. 2) i. 3 All living organisms are composed of cells.
- 1887 J. RUSKIN Præterita II. x. 336 That quality of beauty which I now saw to exist through all the happy conditions of living organism. 1996 Blueprint July-Aug. 26/2 In developing from the New York Deconstructivist Show,..Libeskind now talks a mean line in civic participation and new patterns of social organism.
- 1946 C. MORRIS Signs, Lang. & Behavior iii. 84 One action rather than another..is ‘required’ by the *organism-environment situation. 1958 New Biol. 26 84 His [sc. man's] social, mental, and technological achievements do not make his 'organism-environment’ relationship less important than that of other animals. 2003 Proc. National Acad. Sci. U.S.A. 100 9892 Our findings illustrate the potential for organism-environment interactions to modify the direction as well as the magnitude of global change effects on ecosystem functioning.
- 1861 G. WILSON & A. GEIKIE Mem. E. Forbes iv. 125 The power of organic chemistry to alter and extend the *organismal sciences was felt and acknowledged by all. 1940 G. S. CARTER Gen. Zool. Invertebr. p. xi, The outlook of these branches of zoology is necessarily organismal, and throughout the book this outlook has been adopted. 2003 Sunday Times (Nexis) 14 Sept. (University Guide) 34 Molecular biosciences; organismal biosciences; pharmacology and pharmacy.