Final answer:
Glycogen from carbohydrates is in limited supply and is used as a source of glucose in times of fasting or when dietary carbohydrates are lacking.
Step-by-step explanation:
Glycogen, a polymer of glucose, is an energy storage molecule in animals. When there is adequate ATP present, excess glucose is shunted into glycogen for storage. Glycogen is made and stored in both liver and muscle. The glycogen will be hydrolyzed into glucose 1-phosphate monomers (G-1-P) if blood sugar levels drop.
The presence of glycogen as a source of glucose allows ATP to be produced for a longer period of time during exercise. Glycogen is broken down into G-1-P and converted into G-6-P in both muscle and liver cells, and this product enters the glycolytic pathway.
Glycogen from carbohydrates would be in a limited supply. It is a source of glucose that can be drawn on when fasting or when glucose is not adequately replenished through dietary carbohydrates.