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Environment Forum

Latest Posts

Definition of living?

Posted by Andrew Bone Tuesday, 13th September 2016

The definition of 'living' may vary, but most scientists are agreed that living things:

- are not necessarily capable of independent movement. A common definition beginner students use for life is 'that it moves on its own', or that it 'grows'. A plant is living, but does not 'move on its own', except perhaps through growth. However, many non-living processes, such as the formation of crystals, involve movement and 'growth' as well.

- living things are capable of reproduction. Sometimes 'self-replicates' is used, but care should be taken here: crystals will grow through a process which could be described as self-replication.

- living things are organisms. These fall into the kingdoms of cellular life: Bacteria, Archaea, and Eukarya. There are also organisms which are non-cellular: viruses and viroids (a simple form of virus with a single strand of RNA and only about 15% as many nucleobases).

Posted by Andrew Bone Thursday, 13th October 2016

Cellular organisms have cell membranes, DNA and capacity for reproduction in common, but otherwise there is a great variety of possible organelles, including the option of a nucleus. Viruses are where the clarity on what is living and what is not gets a little less clear: viruses do not carry all the reproduction equipment of their own, so have to hijack the DNA of a eukaryote to reproduce.

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