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I was reading a book and it said that internal/intrinsic growth is defining property of life and not extrinsic growth as saying accumulation of dust on a book makes it a bit bigger, even if it is by a few mm but since it's just a deposition of material and it can be removed, so it's not living. Now, if we see intrinsic growth then I had a doubt. Say we took a piece of log and dipped it into the water. Then the log will also grow in size and this growth is from inside, but the log of wood isn't living. So, I was in doubt that how can I define growth for a living.

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    $\begingroup$ There has been a lot of debate on this topic actually and there is no universally agreed upon definition of life. Almost any point that you raise can be refuted with a non-living counter example. Therefore, I think that this question will most likely accumulate answers that are primarily based on opinions rather than facts. However, if you just refer to growth in living systems it almost always means replication (of cells/genetic material). $\endgroup$ – WYSIWYG Mar 12 '19 at 14:30
  • $\begingroup$ All rudimentary definitions of life I've ever come across include growth as only one of many properties. I doubt a log of wood also conducts reproduction, homeostasis, or metabolism (to list a few other features). Similarly, a computer virus reproduces, thermostats self-regulate, and abiotic chemicals may 'metabolise', but somehow these don't confound us. I think the questioner can't proverbially see the wood for the trees :-) $\endgroup$ – S Pr Mar 12 '19 at 14:55
  • $\begingroup$ Actually this question came in my mind when I encountered a question that said whether plasma membrane is living or not.My mind instantly drifted towards coacervates prepared by some scientists in order to explain that how 1st form of life would have originated. Then I thought that if I prepare a phospholipid bilayer and add all sorts of protein and stuff in it,can I call it living? Will it show growth? If not then what is life and what is living. How do we define growth in a way that it can best explain life. $\endgroup$ – Abner Alfred Thompson Mar 12 '19 at 16:21
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If you are just asking what does growth mean in the context of living systems then it almost always means replication of a unit: cell or genetic material (cell division, DNA replication etc).

Note that increase in cell volume or the inter-cellular space (accretionary growth) also happen in living systems and they are also considered growth. However, at a gross level these processes are indistinguishable from what is happening to wood that is dipped in water.

So growing is not an exclusive feature of living systems but still one of the defining features.

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