Explain the need to use more complex ways of reproduction for most of multi-cellular organisms.

Explanation

Fragmentation is a simple reproductive method for some multi-cellular organism whose body organisation is simple. e.g., Spirogyra, mycelial fungi.
Many multi-cellular organisms show higher body organisations, hence in these organisms reproductive method is complex. Specialised cells are organised as tissues, which in turn are organised into organs. Such tissues and organs are at definite position in body. Different cell types perform different specialised functions in such organisms. Reproduction in such organisms is by specific cell type. So, cell-by-cell division would be impractical in them. Due to this mostly all multi-cellular organisms use more complex ways to reproduction.