Complex sentence: Glycogen is the analogue of starch, a glucose polymer and energy storage in plants, having a similar structure to amylopectin (a component of starch), but more extensively branched and compact than starch.
Split into simpler sentences: Glycogen is the analogue of starch, a glucose polymer that functions as energy storage in plants. It has a similar structure to amylopectin (a component of starch), but is more extensively branched and compact than starch.