Difference between Starch and Cellulose: Overview, Questions, Preparation

Starch is a complex chemical that is produced by plants during photosynthesis. It is a polysaccharide in nature that comprises amylose and amylopectin. Both of the polymers are insoluble in water. It is mainly present in potatoes, rice, cereals, bread and many other food items. Human beings need to consume starch in their diet as it provides energy to our body tissues. It also offers other health benefits like it lowers our increased insulin level or glucose level. It is also used as a thickening agent in baking cakes and pastries, a bulking agent in dairy items, a binding agent in soups and sauces, and a sweetening agent in beverages.

Cellulose is a complex carbohydrate that is made up of hundreds or thousands of glucose units. It helps the plants to stay firm. It is present in plant walls. Unlike starch, humans are incapable of digesting cellulose. Cellulose is insoluble in water as compared to starch which is soluble in water.

Starch and cellulose are polymers with very similar properties. They both are made of the same monomer. The monomer is glucose, and both consist of the same glucose-based repeat units. But, there is a structural difference between starch and cellulose.

In starch, the glucose repeat units are linked together in such a manner that they are all in the same orientation. Whereas, in cellulose, the glucose repeat units are linked together so that alternating molecules are rotated 180 degrees from each other.

This orientation of glucose-based repeat units increases the strength and makes cellulose stronger than starch. The cellulose fibres form rigidity by stacking up just like corrugated sheets piled on top of each other. The starch fibres are tied to each other weakly because of their structure and can break easily compared to cellulose.

To see the structural difference between starch and cellulose in detail, study this formation.

• Cellulose is a straight-chain polysaccharide of β-D-glucose units joined by C1-C4 glycosidic linkage (β-link)

• Starch is made up of two elements; 

Amylose - Amylose is made up of ∝-D- glucose units, which is linked to each other by C1-C4 glycosidic linkage, forming a linear chain.

Amylopectin - Amylopectin is made of a linear chain of ∝-D-glucose units, linked to each other by C1-C4 glycosidic linkage and then branching happens by C1-C6 glycosidic linkage. 

The cellulose is well explained in Class 11 textbooks. There is a diagrammatic representation of a portion of glycogen, to explain the cellulose. The cellulose is described as a polymeric polysaccharide. Similarly, starch is also described with its molecular structures.

The starch and cellulose are further explained in class 12 books with their basic and structural difference. In class 12 textbooks, the structural difference between cellulose and starch is described in more details with the structure of glucose repeat units. 

In class 12 boards, the Biomolecules chapter holds 4 marks. 

[Image courtesy: NCERT]