a)Human beings do not have cellulose-digesting enzymes
Cellulose-rich food substances are a good source of roughage for human beings because human beings do not have cellulose-digesting enzymes. Thus, it cannot be digested by humans and acts as a good source of roughage.Humans cannot digest cellulose because they lack the enzymes essential for breaking the beta-acetyl linkages. The undigested cellulose acts as fibre that aids in the functioning of the intestinal tract.Cellulose is a polysaccharide that makes 30% of the plant cell wall. It helps in connecting cells to form tissues and signals the cells to grow and divide. Humans cannot digest cellulose. However, it is consumed in the diet as fibre. Fibre helps the digestive system to keep the food moving through the gut and moves the waste out of the body.