The difference between a multicellular organism and a colonial organism is that colonial organism consists of individual one-celled organisms that can, if separated, survive on their own. On the other hand, cells from a multicellular life-form cannot live independently (they are all connected to function together).
Volvox is not considered multicellular because its cells are not aggregated into organized tissues and have no organ and organ systems.
3. Environment
The simplest definition of an ecosystem is that it is a community or group of living organisms that live in and interact with each other in a specific environment.
