Eli5: why are single cells so small? What’s the maximal size a single cell?

Question

What is the maximal possible size of a single cell organism? Why can’t a single cell be the size of a coin for example?

In: Biology

Answer 1

Cells are typically small because of the square-cube relationship. The stuff inside the cell is proportional to the cube of the length, but each bit of stuff needs to exchange energy and waste with the environment, and this happens at the surface, which is proportional to the square of the length. If the cell gets too big the amount of access to the environment per bit of stuff inside the cell drops below a sustainable level and the cell dies.