Final answer:
The characteristic being described is that an amoeba is a unicellular organism.
Step-by-step explanation:
The characteristic of living things being described in the question is that an amoeba is a unicellular organism. Unicellular organisms, like amoebas, are made up of only one cell. They carry out all necessary functions for life within that single cell, including reproduction, obtaining and digesting food, and excreting waste.