sentences:  Plants, but not animals, synthesize phytoecdysteroids from mevalonic acid in the mevalonate pathway of the plant cell using acetyl-CoA as a precursor.Over 250 ecdysteroid analogs have been identified so far in plants, and it has been theorized that there are over 1,000 possible structures which might occur in nature.Many more plants have the ability to "turn on" the production of phytoecdysteroids when under stress, animal attack or other conditions.