Step 1: Understanding the Concept
Glycogen is a branched polymer of glucose joined by glycosidic bonds and stored mainly in the liver and muscles.
Step 2: Breakdown
When blood sugar falls, these bonds are split with the help of enzymes (glycogenolysis), and water takes part in breaking each bond.
Step 3: Name the process
Breaking a polymer into monomers by adding water is hydrolysis. Glycolysis is the later breakdown of glucose into pyruvate.
Final Answer:
Glycogen is converted into glucose by hydrolysis.
\[ \boxed{\text{(B) }\text{hydrolysis}} \]