Cellulases break down cellulose and are a form of carbohydrase. Cellulase hydrolyses cellulose into the smaller units of monosaccharide (glucose) and disaccharide (cellobiose). It’s found in the digestive juices of some wood-boring insects and various microorganisms but not in mammals.
Cellulose is the substance, which makes up most of a plant’s cell walls and is the primary building material for plants. Because it’s made by all plants, it’s probably the most abundant organic compound on the Earth.
Since cellulose is the main building material out of which plants are made, and plants are the first link in the food chain cellulose is indeed a very important substance. The French chemist Anselme Payen (1795–1871) was the first to isolate it and earlier had isolated the first enzyme. While studying different types of wood, Payen obtained a substance, which he knew was not starch. Starch is glucose or sugar in its stored form. The substance still could be broken down into its basic units of glucose the same way starch can be. Payen named this new substance cellulose because he had obtained it from the cell walls of plants.