an organism is any living thing that functions as an individual… such a definition is not very clear
organisms are between organ systems and populations in biological organization
“organismality” is a proposed concept where there are multiple levels of how organism something is, defining degrees of cooperation and complexity
| level | example | composition | metabolism, growth, reproduction | co-operation |
|---|---|---|---|---|
| virus | tobacco mosaic virus | nucleic acid, protein | no | no metabolism, so not living, not an organism, say many biologists; but they evolve, their genes collaborating to manipulate the host |
| unicellular organism | paramecium | one cell with organelles | yes | inter-cellular signaling |
| swarming protistan | dictyostelium | unicellular amoebae | yes | free-living unicellular amoebae for most of lifetime; swarm and aggregate to a multicellular slug, cells specializing to form a dead stalk and a fruiting body |
| multicellular organism | mushroom-forming fungus | cells, grouped into organs for specific functions | yes | cell specialization, communication |
| permanent sexual partnership | anglerfish | male and female permanently fastened together | yes | male provides male gametes; female provides all other functions |
| mutualism | lichen | organisms of different species | yes | fungus provides structure, absorbs water and minerals; algae does photosynthesis |
| joined colony | siphonophore | zooids joined together | yes | organism specialization; inter-organism signaling |
| superorganism | ant colony | individuals living together | yes | organism specialization; inter-organism signaling |