Cell Size: Cells never get too large because:
1. limits on diffusion
faster passage across membrane in small cells than large.
more efficient communication throughout cytoplasm (smaller cells have less volume, so less distance for molecules to travel)
2. limits of surface-to-volume ratio
A small volume / surface area (small cells) allows molecules to reach all parts of cell the quickest.
Interaction with outside occurs only at surface (at the plasma membrane). Surface area of large cells is not large enough to allow quick diffusion of needed molecules into the large volume of those cells.
Cell Surface Area vs. Volume (McGraw Hill)
Cell Surface Area vs. Volume (BioCourse.com) - Requires Shockwave
