How are the modes for reproduction different in unicellular and multi-cellular organisms?

The organisms with single-celled body organisation are referred to as unicellular organisms. Being single-celled, cell division in these organisms gives rise to offspring (mainly asexual reproduction) and therefore, there is no need of special organ system for the process of reproduction. For example, binary fission in Amoeba takes place by enlargement of the cell and increasing cell content followed by division of mother cell into two daughter cells, each of which is now offspring Amoeba. Other methods of reproduction in unicellular organisms include fragmentation, fission, budding etc. Multicellular organisms consist of multiple cells which are organised into tissues, organs and organ systems. Owing to the complexity of their body organisation, they have specialised reproductive system and reproduce by sexual reproduction.