* Cell Size Limits: Cells have limitations on how big they can get. A larger cell has more difficulty getting nutrients in and waste products out. This is due to the surface area to volume ratio - as a cell grows, its volume increases faster than its surface area.
* Organism Size Through Numbers: Larger organisms generally have more cells, not necessarily larger cells. This allows for specialized tissues and organs to develop.
Example: A blue whale is the largest animal on Earth, but its cells are roughly the same size as a human's cells. The whale is just made up of many, many more cells.
In conclusion: Cell size is generally constrained by their function and the limitations of diffusion. Organisms get larger by having more cells, not by having bigger cells.
