In other words, if you selected a currently living eukaryotic cell at random, would it be a single-celled organism or part of some multicellular entity?
I think the answer to the question is clear when we look at all cells in general: the vast majority will be prokaryotic, the vast majority of which (though, I was surprised to recently learn, apparently not all) are unicellular. But what about if we focus on cells with a nucleus? Do the protozoans, microalgae, yeasts and whatnot outnumber the cells contained in macroscopic animals, plants, and fungi?
Global biomass is overwhelmingly plants - by which is meant kingdom Plantae, sensu strictissimo, which is multicellular by definition and excludes protists.
Also note even if we were using the more general sense of “plant” that includes protists, land biomass is two orders of magnitude larger than biomass in the ocean, which is where most of the protists live. So it’d still be plants. Probably most numerically, parenchyma and not-yet-dead sclerenchyma cells.
Ah, thanks. I had stumbled across the biomass breakdown before, but was unsure about the definition of ‘plant’ used (it was some popular outlet that didn’t cite the source).
The only niggling question is whether biomass is a good indicator—if we were to use it also for prokaryotic cells, we’d get a miscount, since these are typically much smaller than eukaryotes. But as long as the average single eukaryotic cell isn’t much smaller than the average eukaryotic cell that is part of a multicellular organism, this seems to settle the question.
Single-celled eukaryotes are often smaller than the individual cells of multicellular organisms. Yeasts, for instance, are quite small as far as cells go, tending less than 3-5 µm . But not generally more than 1 order of magnitude smaller than most cells. The cells of multicellular organisms tend to be 10-100 µm in largest dimension.