$6$Carbohydrates are essential for life in both plants and animals. Carbohydrates are used as storage molecules as starch in plants and glycogen in animals. Chemically they are polyhydroxy aldehydes or ketones. On the basis of their behaviour on hydrolysis, carbohydrates are classified as monosaccharides, oligosaccharides and polysaccharides. All monosaccharides are reducing sugars, i.e., they are oxidized by Tollens' reagent and Fehling's solution. A monosaccharide like glucose is aldohexose and its molecular formula was found to be $\displaystyle \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$. After reacting with different reagents like $\displaystyle \mathrm{HI}, \mathrm{H}_{2} \mathrm{~N}-\mathrm{OH}$, Bromine water, $\displaystyle \left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}$, etc. its structure was found to contain one aldehyde group, one primary alcoholic group, $\displaystyle \left(-\mathrm{CH}_{2} \mathrm{OH}\right)$ and four secondary alcoholic groups ( > CHOH). Despite having the aldehyde group, glucose does not give some of the reactions of aldehyde group like Schiff's test, $\displaystyle \mathrm{NaHSO}_{3}$ addition. This explains the existence of glucose in two cyclic hemiacetal forms which differ only in the configuration of the hydroxyl group at C - 1 . Answer the following questions : (a) What are reducing sugars ? (b) Classify the following into monosaccharide and disaccharide : Fructose, Sucrose, Lactose, Galactose (c) Name the polysaccharide which is known as 'animal starch'. Why is it called 'animal starch' ?

OR

(c) (i) Name the isomers of glucose which in the cyclic form differ only in the configuration of the - OH group at C - 1. (ii) Presence of which functional group was detected when glucose reacted with $\displaystyle \mathrm{Br}_{2}$ water ?

Chemistry · Biomolecules