Question

Why are larger organisms made up of greater number of cells ?

Answer 1

larger organisms developed from more smaller cells rather than simply growing larger cells.
If cells grow too large, they cannot continue to function well. These are the main reasons:
1. Diffusion doesn't happen fast enough to supply the materials and take away the wastes from a cell that is too large. The interior of the cell is too far away from the plasma membrane.
2. The DNA can't be copied fast enough to handle the protein needs of a large cell.
3. The surface area to volume ratio is too small in a cell that is too large. Since materials must enter and leave the cell through the plasma membrane, the plasma membrane must be big enough to handle all these transfers. In a cell that is too large, the plasma membrane isn't large enough to handle it.