Cellulase by definition is any of several enzymes produced chiefly by fungi, bacteria, and protozoans that catalyze the hydrolysis of cellulose. Cellulase is an enzyme that breaks down cellulose, the carbohydrate that is the main part of the cell walls of plants. Cellulose is nondigestible by humans because we to not produce the enzyme cellulase. The human body does not produce cellulase, but, it is available for supplementation since it can help us break down plant material more thoroughly, thereby getting the most from the plants that we eat.