The correct answer is option 4, the liver. The liver is primarily responsible for storing glycogen. Glycogen is a form of glucose that is stored as a reserve for times when the body requires energy. It serves as a quick source of energy when needed. The liver can store up to around 10% of its weight in glycogen. The other options mentioned in the question, such as the spleen, pancreas, and gastric glands, do not store glycogen to a significant extent. The spleen primarily functions in maintaining healthy blood cells, while the pancreas produces and releases insulin and plays a role in regulating blood sugar levels. Gastric glands produce stomach acid and digestive enzymes.