From Liquipedia StarCraft Brood War Wiki
Biological units are made fully or partially out of living organic tissue.
- Science Vessel's Irradiate harms only the listed units.
- Medic's Heal ability works only on biological ground units.
- Dark Archon's Maelstrom affects only biological units.
- The SCV is also a mechanical unit.
- The Queen's Spawn Broodlings affects ground-based biological units as well as tanks and goliaths.