Question

What type of molecule do animal cells use for long-term energy storage?

Answer 1

Glycogen.
Glycogen is a multibranched polysaccharide that serves as a form of energy storage in animals. They're stored inside the liver and muscles.

Answer 2

FAT
"Glycogen is a multibranched polysaccharide that serves as a form of energy storage in animals and fungi. In humans, glycogen is made and stored primarily in the cells of the liver and the muscles, and functions as the secondary long-term energy storage (with the primary energy stores being fats "
Read more at: http://en.wikipedia.org/wiki/Glycogen