What stores glucose in the liver for later use?

Glycogen is the correct answer because it is the primary form in which glucose is stored in the liver and muscle tissues. When you consume carbohydrates, your body breaks them down into glucose, which can be used immediately for energy. However, any excess glucose needs to be stored for future energy needs, and this is where glycogen comes into play.

Glycogen is a polysaccharide made up of many glucose units linked together. The liver can store a significant amount of glycogen, which can then be converted back into glucose and released into the bloodstream during times of fasting or increased energy demand, such as between meals or during exercise. This process helps in maintaining blood glucose levels and providing energy to the body.

The other options do not function as glucose storage in the liver: Starch is a storage form of glucose found in plants, while fructose is a simple sugar that can be metabolized but is not stored in the liver in the same way as glucose. Protein, on the other hand, is primarily used for building and repairing tissues and does not serve as a glucose storage form.