Chapter 23, Problem 4TE

In what ways are cellulose and starch similar to each other? In what ways are they different from each other?

To determine

The ways in which cellulose and starch are similar to each and are different to each other.

Answer to Problem 4TE

The monosaccharide which is similar in the structure of starch and cellulose is glucose. They both are having different physical and chemical properties.

Explanation of Solution

The starch is not a single compound, it is considered as a mixture of two components. The first component is water soluble and is named as amylose. The second component is water insoluble and is named as amylopectin.

Amylose is a liner polymer of glucose in which ${\text{C}}_1$ of one glucose unit is attached to ${\text{C}}_4$ of the other through glycoside linkage. However, amylopectin is a highly branched chain polymer of glucose. It consist of hundreds of short chains each containing $20-25$ glucose units. These repeating units in starch are joined together by $\alpha \text{-}$ glycosidic linkage.

The cellulose on the other hand is a biomolecule which is composed of $300-3000$ glucose units. The molecular mass of cellulose varies from $50000$ to $500000$ . These repeating units in cellulose are joined together by $\beta \text{-}$ glycosidic linkage.

Therefore, the monosaccharide which is common in the structure of starch and cellulose is glucose.

Starch and cellulose both are non-reducing sugars. They both do not reduce Tollens’ reagent or Fehling’s solution.

The physical and chemical properties of both starch and cellulose are somewhat different.Starch is a white amorphous powder sparingly soluble in water. The hydrolysis of starch with dilute mineral acids results in the breakage of starch molecules into smaller molecules like maltose and finally into D-glucose. However, the hydrolysis of cellulose does not take place easily. As the result of heating with dilute mineral acid it give only D-glucose.

Conclusion:

The ways in which starch is similar to cellulose are that they both are the non-reducing sugars and are polymer of glucose units. The way in which they both are different is that starch is hydrolysed in the presence of dilute acid whereas cellulose does not get hydrolysed under same condition.