Cellulose (see diagram below) is linear polysaccharide—“poly” for many and “saccharide” means sugar, so cellulose is a chain of sugar molecules. It’s an amazing molecule: it’s the most abundant organic compound on the planet because it is the main component in plant cell walls. Cellulose is highly crystalline because of the way the sugar molecules are connected and because of the fact that it’s made up of a single enantiomer of glucose. Like polypropylene, highly crystalline polymers like cellulose are very strong—strong enough to make trees stand up straight.