* Self-sufficiency: They can obtain nutrients, produce energy, eliminate waste, reproduce, and respond to their environment, all within the boundaries of their single cell.
* All essential functions in one: Unlike multicellular organisms, they don't rely on specialized cells or tissues for specific tasks. Each cell is a self-contained unit.
* Independent existence: Unicellular organisms can exist independently and thrive without needing to be part of a larger organism.
Example: A single-celled bacterium like E. coli can carry out all the necessary functions for survival and reproduction on its own.
It's important to note that "complete" in this context doesn't mean they are as complex as multicellular organisms. They have simpler structures and processes, but they are complete in the sense that they can function as independent living entities.
