Question: why are cells small

Zoe Vance answered on 11 Feb 2025:

I think it’s probably related to surface area vs. volume! As a cell gets bigger the inner volume where all the reactions to keep the cell alive happen would increase a lot faster than the surface area of the outside where things like nutrients and outside signals have to come in so at some point I’d assume it isn’t at an optimal ratio anymore.

There is also some variation in the sizes of cells, for example a human egg cell is usually visible to the naked eye. I had a look about for the largest known cell and most people either say ostrich egg or some kind of algae if you’re looking for a whole organism that’s just a single cell (Valonia ventricosa which gets to a couple of inches or Caulerpa taxifolia which can get to about a foot and looks like a plant!). Those are pretty unusual cases though where it seems like the ‘single’ cell is actually more like a lot of cells joined up together. Interesting question!