Answer: Glycogen
Explanation:
It provides long-term energy storage.
Further Explanation
Living organisms require energy in order to undertake their daily activities such as growth and development, locomotion, gaseous exchange, etc. To do so they obtain nutrients for short-term and long-term energy source.
Carbohydrates are the major energy source for living organisms, however, living organisms may use other sources of energy such as proteins or fats when carbohydrates is out of stock or not available.
Energy source in animals
Animals use simple carbohydrates such as glucose obtained from diet for short-term energy sources.
These simple carbohydrates may also be stored for future use in the form of glycogen, which makes glycogen a long-term energy source, to be used when need arises.
When glucose levels are low in the body hormones in the body trigger the breakdown of glycogen to glucose.
Other sources of energy such as proteins and fats are used when carbohydrates storage is depleted, for example during starvation.
Energy source in plants
In plants, on the other hand, simple carbohydrates are similarly used as a short term source of energy. Additionally, simple molecules such as glucose are stored in the form of starch for long-term source of energy for the plants.