Q.(i) What is the basic structural difference between starch and cellulose? (2 marks)

The two important polysaccharides found in plants are starch and cellulose.

Concept. Polysaccharides are long condensation polymers of monosaccharide units joined by glycosidic linkages. In plants:

• Starch — the food-storage polysaccharide, a polymer of $\alpha$-D-glucose consisting of amylose (linear) and amylopectin (branched). …

Cellulose is a polymer of thousands of glucose units (a polysaccharide); maltose and sucrose are disaccharides and fructose is a monosaccharide. Answer: (d).

• Maltose = glucose + glucose (disaccharide).
• Sucrose = glucose + fructose (disaccharide). …

Both are glucose polymers, but they differ in the type of glycosidic linkage joining the glucose units — $\alpha$ in starch, $\beta$ in cellulose — which changes the overall shape and digestibility of the polymer.

Structural comparison

• Starch is a polymer of $\alpha$-D-glucose units. It consists of two components: amylose (a long unbranched chain of glucose units joined by $\alpha(1\rightarrow4)$-glycosidic linkages, which coils into a helical structure) and amylopectin (a branched-chain polysaccharide of glucose units joined mainly by $\alpha(1\rightarrow4)$ linkages, with branching through $\alpha(1\rightarrow6)$-glycosidic linkages roughly every 25 units).
• Cellulose is a polymer made up only of $\beta$-D-glucose units, joined exclusively by $\beta(1\rightarrow4)$-glycosidic linkages, forming a long, straight, unbranched chain. These linear chains run parallel and are extensively hydrogen-bonded to each other, giving cellulose fibres great mechanical strength (as in the plant cell wall). …

Glycogen is the reserve carbohydrate stored in the animal body, hence "animal starch" — option (c).

Starch is a mixture of two glucose polymers — the linear, helical amylose and the highly branched amylopectin.

Starch, the storage polysaccharide of plants, is composed of two distinct components, both built from $\alpha$-D-glucose units:

1. Amylose (≈15–20% of starch): a linear, unbranched chain of $\alpha$-D-glucose units joined by $\alpha(1\rightarrow4)$ glycosidic linkages. It coils into a helical shape and is responsible for the blue-black colour starch gives with iodine (iodine molecules slot inside the helix). …

Cellulose, the structural polysaccharide of plant cell walls, is the most abundant carbohydrate (and organic compound) on Earth.

Cellulose is a straight-chain polymer of beta-D-glucose units joined by beta-1,4-glycosidic linkages. It forms the structural framework of plant cell walls and, since plants dominate the biosphere, it is the single most abundant carbohydrate in nature. Glucos …

Starch, the storage polysaccharide in plants, is a mixture of two glucose polymers: amylose and amylopectin.

Starch is made of two components:

• Amylose (~15-20%): a long unbranched chain of alpha-D-glucose units joined by C1-C4 glycosidic linkages; it is water-soluble and responsible for the blue colour with iodine.
• Amylopectin (~80-85%): a branched-chain polymer of alpha-D-glucose, with branching occurring through C1-C6 glycosidic linkages; it is insoluble in water. …

Starch is a naturally occurring polysaccharide, built entirely of α-D-glucose units (as amylose and amylopectin) synthesised by plants — it is a natural, not artificial, polymer.

The statement is False.

Starch is a polysaccharide (a carbohydrate biomolecule), made of a very large number of glucose units joined by glycosidic linkages. It occurs naturally in plants (seeds, tubers, roots) as the main storage form of energy, and consists of:

• Amylose (15–20%): a long unbranched chain of $\alpha$-D-glucose units linked by C1–C4 glycosidic bonds.
• Amylopectin (80–85%): a branched-chain polymer with additional C1–C6 branch linkages. …

Part (a): starch = $\alpha$-glucose, $\alpha$-(1→4)/(1→6) links (helical, digestible); cellulose = $\beta$-glucose, $\beta$-(1→4) links (linear, indigestible). Part (b): DNA hydrolyses to 2-deoxyribose, phosphoric acid, and the bases A, G, C and T.