Which of the following is a naturally occurring polymer important for life?

Cellulose is a naturally occurring polymer that plays a crucial role in the structure of plant cell walls, providing rigidity and strength. It is composed of long chains of glucose units linked together by glycosidic bonds, forming a complex network that helps maintain the integrity of plant cells. This structural aspect is vital for maintaining the shape and stability of plants, allowing them to stand upright and grow towards sunlight.

The importance of cellulose extends to its function in the human diet, where it acts as dietary fiber. While humans cannot digest cellulose, it supports digestive health by promoting regular bowel movements and providing bulk to the diet.

In contrast, the other substances listed do not qualify as polymers in the same sense. Sucrose is a disaccharide made from glucose and fructose, cholesterol is a type of lipid rather than a polymer, and ATP (adenosine triphosphate) is a nucleotide that serves as an energy carrier in cells but is not a polymer in the way that cellulose is.