Question

The iodine test can be used to detect starch but not cellulose because

• A. cellulose has a linear structure
• B. cellulose is the branched polymer of α - D Glucose
• C. cellulose contains '1−4' glycosidic linkage
• D. cellulose is a structural polysaccharide

Answer 1

The correct option is A cellulose has a linear structure

Cellulose is an unbranched, linear homopolysaccharide of $\beta -D-\mathrm{glucose}$joined by $\beta -1,4-\mathrm{glycosidic}\mathrm{bonds}$


Starch, on the other hand, is a homopolymer of $\alpha -D-\mathrm{glucose}$consisting of two components viz amylose and amylopectin.


Amylose is helical in structure and can hold $I_2$ molecules whereas cellulose, being linear, cannot hold $I_2$. Hence, the iodine test can not be used to detect cellulose in a solution.