Question

why multicellular organism use sexual mode of reproduction

Answer 1

most of the times the cells exists in millions or more thus asexual reproduction is not possible of such complexity so sexual reproduction is adopted

Answer 2

As the multicellular organisms have complex body design, if they reproduce asexually they will not be able to develop as per the need and will not develops necessary complex body designs... hence sexual mode of reproduction is required by which when two gametes fuse they provide variation to the progeny ..the multicellular organisms have evolved in such a way that they can't reproduce asexually as per their body designs.. except some