It would take 500 average - size cells to equal the size of the period at the end of this sentence. So it is not surprising that the functions of a cell are invisible to the unaided eye.
Uz punkta šī teikuma beigās varētu novietoties 500 vidēja izmēra šūnas, tāpēc, kā viegli saprast, šūnā notiekošie procesi ar neapbruņotu aci nav novērojami.