The cell organelle with a tail-like appendage is the flagellum.

Here's why:

* Flagella are long, whip-like structures that extend from the cell surface. They are used for locomotion (movement) in some single-celled organisms like bacteria and sperm cells.

* The "tail" of the flagellum is actually a complex arrangement of microtubules, which are protein filaments that slide past each other to create the whipping motion.

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