Cellulose is the most abundant organic polymer on Earth, accounting for 30% of non-fossil organic carbon. Other polymers in plants include hemicellulose, lignin, and pectin. Chitin and keratin are the most abundant outside of plants, with chitin found in fungi and arthropods and keratin in nails, hair, and scales.
The most abundant organic polymers on Earth are cellulose (which accounts for about 30% of non-fossil organic carbon), lignin (~30%), hemicellulose, pectin, chitin and keratin. Cellulose is the most common of the organic polymers in plant cell walls, accounting for the majority of terrestrial biomass. Overall, about 33% of plant matter is cellulose. Cotton is 90% cellulose, while wood is about 50%.
Cellulose is famous for being the most abundant of the Earth’s polymers. Used in every plant, it is excreted by some bacteria as a biofilm. Cellulose is the main component of cardboard and paper. To make paper, it is ground into a pulp, bleached, then formed into sheets. For most animals, such as humans, cellulose is indigestible and is the “dietary fiber” that serves as the bulking agent for our feces. Some animals, such as ruminants and termites, have special bacteria that live in their guts to help break down cellulose and make it digestible.
Other organic polymers found in large quantities in plants include hemicellulose, lignin and pectin. These make up the majority of vascular plants and perform several functions. For example, hemicellulose is non-crystalline unlike cellulose, consists of shorter molecular chains and has a branched structure whereas cellulose does not. Lignin makes up one-quarter to one-third of wood’s dry mass, making it the second most abundant of organic polymers.
Not counting plants, the most abundant organic polymers are chitin and keratin, in that order. Chitin forms most of the cell walls of fungi and the exoskeletons of all arthropods, including insects and crustaceans, both of which are extremely numerous. The amount of chitin found in nature probably exceeds the dry weight of all terrestrial vertebrate biomass. Insects are constantly mass producing and discarding it when they molt.
Keratin is one of the organic polymers we are most familiar with, making up most of the hard but non-mineralized structures in reptiles, birds, amphibians and mammals. In particular, keratin is the main component of nails and hair in mammals, scales and claws in reptiles, many parts of birds including feathers and make up the exoskeletons of arthropods together with chitin.
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