Question

Ankita bought some glucose powder. She felt it was adulterated with starch powder. How would she test it?
A. By sieving
B. By dissolving it in water
C. By iodine test
D. All of the above

Answer 1

Hint: Polysaccharides are the polymers of more than ten monosaccharides interlinked by glycosidic bonds formed by dehydration synthesis. Different polysaccharides differ in the nature and number of their monosaccharides and degree of branching. Starch is an example of storage polysaccharide in plants.

Complete answer:
Polysaccharides are of two types- homopolysaccharides and heteropolysaccharides.
Homopolysaccharides are formed of only one type of monosaccharides, for example, cellulose, starch, glycogen, inulin, agar, xylan, araban, etc.
Heteropolysaccharides are formed of two or more types of monosaccharides or their derivatives like amino sugars like glucosamine, N-acetyl galactosamine or sugar acids like glucuronic acid, etc.
Starch is a storage homopolysaccharide of plants and is found as species specific shaped and sized grains in the potato tubers, corn seeds, cereals like rice, wheat, etc. and fruits like banana, mango, etc. Chemically the starch is formed of two glucose polymers: a-amylose which is an unbranched but spiral chain of about 200-2000 alpha glucose molecules interlinked by alpha (1,4) glycosidic bonds and amylopectin which is a branches glucan of about 2000 to 20000 alpha glucose molecules so forming a helical secondary structure. Glucose molecules are interlinked by alpha (1,4) glycosidic bonds except the bond between the glucose of the main chain and the first glucose of the branch which is a (1,6) glycosidic bond. Starch can hold iodine molecules in the helices so gives blue colour with iodine.
So, the correct answer is “Option C”.

Note: Carbohydrates are important biomolecules formed of carbon, hydrogen and oxygen. These are classified into monosaccharides and polysaccharides. Monosaccharides are simplest carbohydrates that are sweeter in taste and called sugars.