glycogen is made up of glucose, but so is starch. what modifications amde glycogen different from starch?

Answer 1

You're right, they're both polymers of glucose. The difference is the patterns of branching formed by their bonds, giving them slightly different chemical properties. They're both still used for storing energy though.

Answer 2

if you want it in numbers:
Starch is 70% amylopectin. In amylopectin, glucose units are linked in a linear way. Branching takes place every 24 to 30 glucose units.

Its counterpart in animals is glycogen which has the same composition and structure, but with more extensive branching that occurs every 8 to 12 glucose units