Complex sentence: Many plants store important chemicals in the form of inactive glycosides; if these chemicals are needed, the glycosides are brought in contact with water and an enzyme, and the sugar part is broken off, making the chemical available for use.
Split into simpler sentences: Many plants store important chemicals in the form of inactive glycosides; which can be activated with water and an enzyme. This causes the sugar part to be broken off, making the chemical available for use.