There are several differences between the reproductive systems of unicellular and multicellular organisms. In unicellular organisms, reproduction occurs by the division of the entire cell. The different types of reproduction in unicellular organisms include mitosis, budding, binary fission, and encysting. In contrast, multicellular organisms use their reproductive organs. Thus, unicellular organisms reproduce by methods like spore formation. In contrast, in complex multicellular organisms like humans and animals, both parents are involved during sexual reproduction.