Wrinkle in Time was, I think, the first SF I ever read, and it was certainly the first book that made a permanent searing lifebond-ish impact on me forever. So yeah.

Ahahahaha. The mitochondria, oh yes. I thought she'd made them up for years. Then I found out they were real! Then I thought farandolae were real. For years. It was... not ideal. Darn you L'Engle!