The word mitochondria is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 22
Highest Scoring Words With Friends™ Plays In The Letters mitochondria
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Seven Letter Word Alert: (31 words)
carotid, cartoon, chariot, chorion, choroid, chroman, coadmit, comonad, conidia, crinoid, diction, domatic, doorman, doormat, dormant, haricot, hominid, manhood, marconi, martini, monarch, monitor, mordant, moronic, nomadic, odorant, omicron, oration, thiamin, tornado, triadic