The nonliving material that makes up the cell walls of plant cells is cellulose. Cellulose is a type of carbohydrate made up of many glucose molecules.
Cellulose protects plant cells and gives them their shape. This substance also makes it possible for plants and trees to grow anywhere from a few inches to hundreds of feet tall. Tall trees sway very little when the wind blows due to the presence of rigid cell walls. Shorter plants have flexible cell walls to allow them to bend in the wind.
Humans are unable to digest cellulose because they lack the enzymes necessary. Undigested cellulose helps the digestive system work properly.