Question

What are constituent units of cellulose?

Answer 1

Cellulose is an important structural component of the primary cell walls of green plants, various forms of algae, and oomycetes. Certain types of bacteria secrete it to form biofilms. The most abundant organic polymer on earth is cellulose. Cellulose is a molecule made up of hundreds, sometimes even thousands, of carbon, hydrogen, and oxygen atoms. Cellulose is the main substance in plant cell walls, which helps plants stand firm and upright.

Complete answer:
Cellulose is an organic compound and the most abundant biopolymer on earth. It is a complex carbohydrate or polysaccharide composed of hundreds or thousands of glucose molecules connected together to form a chain. Although animals do not produce cellulose, it is produced by plants, algae, and some bacteria and other microorganisms.
Cellulose is a type of polysaccharide, which is connected by linear glucan chains through $\beta {\text{ }}1,4$ glycosidic bonds, and uses cellobiose residues as repeating units with different degrees of polymerization (DP). It is packed into microfibrils using intramolecular hydrogen bonds as well as intermolecular van der Waals forces.
Although cellulose polymorphs have been recorded, X-ray diffraction analysis shows that natural cellulose appears as cellulose I, which is a mixture of polymorphs I $\alpha$ and I $\beta$. Cellulose I $\alpha$ is synthesized at the same time as the microfibril network extension. The microfibril network is dominant in some bacteria and lower plants to form primary walls, but I $\beta$ cellulose is mainly deposited on the secondary walls of higher plants to improve strength.

Note:
Humans cannot digest cellulose, but it is very important as fiber in the diet. Fiber helps your digestive system by keeping food passing through the intestines and expelling waste from the body. Cattle, sheep, horses and other animals can digest cellulose, so they can get the energy and nutrients they need from grass.