Question

why can't single grow vry large or big organisms are multicellular why.?? why can't such organisms be a single large cells ??

Answer 1

Because in such a large body one cell cant handle every function.

Answer 2

1) Large area means more requirnent of O2 which cant be obtained by simple diffusion 2) big cell req more food which cant be gained in direct way so it req complex machanism 3) cells are very delicate so cant grow large in size without accumlation of other cells 4) cell reproduce by binarry fission where the sigle cell splits into two new cells which will be difficult in large cells