That is fairly close to the size of the smallest cells - the mycoplasmas. Also, if the cell volume is too small, on the average there will be a very small number of molecules contained within the cell. Even if there are a finite, but very small, number of molecules in a cell, random concentration fluctuations will be huge. If the concentration of some molecule or ion fluctuates greatly, there is an unstable cellular environment. Endoplasmic reticulum, mitochondria, chloroplasts, microtubules, and microfilaments are among the structures associated with eukaryotes.
Multicellular organisms consist of eukaryotic cells.