Question

complex multicellular organisms cannot give rise to complete individual from their cut body parts . they mostly belong to higher group of organisms​

Answer 1

The reason is that in multicellular organisms they have a specific body part with which they could reproduce and in the case of Hydra they don't have such organs.

another reason is that there is very less chance of organisms produced to survive because the individual cells of multicellular organisms cannot carry out all the Groups of cells form tissues and organs, which perform different functions