[CBSE AIPMT 2003]
Correct Option (d)
Reason : During biogas formation, digestion of cellulose is slow (rate-limiting) and most of the lignin is not decomposed. After cellulose lignin is the most abundant plant polymer. It forms 20 to 30% of the wood of the tree. Lignin is a complex polymeric molecule, made up of phenyl propanoid units. Cellulose is a large chained polymer of glucose molecules which are linked with each other by glycosidic bonds. Hemicellulose are branched polymers of glucose, xylose, galactose, mannose and arabinose.