Organelle
An organelle was any part of a  with a specific function.

In 2374, after Seven of Nine's separation from the Borg, her Human immune system restarted and rejected anything Borg, including her Borg organelles. ()

Later that year, Seven's dormant Borg nanoprobes reactivated and caused a high concentration of Borg organelles to appear in her bone marrow and lymphatic tissue. ()

Mitochondria were a type of organelle. In a botany lesson for Naomi Wildman in 2375, The Doctor pointed out such an organelle and described its form as "like a little bitty potato." ()

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Anatomy