Answer:
No, there are some organisms that only have one cell, although there are organ systems that are made up of many cells. Not all organisms have organ systems.
Explanation:
For example, the Trichoplax. It is an animal with no organs that is tiny and multicellular, and only feeds on microalgae. A Trichoplax are flat organisms about a millimetre in diameter with no internal structures and typically have two cellular layers. These organisms live in the oceans and seas all around the world but are not necessarily found in their natural habitat, more so in captivity such as a marine aquarium. Trichoplax are found to live in symbiosis with such things as bacteria and others in the oceans and seas.
