Fructose, Sucrose, Starch, Cellulose, Glycogen - UNSOLVED PRACTICE SET

Q7. Distinguish between amylose and amylopectin in terms of structure and properties.

Q8. Why is cellulose insoluble in water despite having many -OH groups? Explain.

Q9. Fructose is a ketose, yet it gives a positive Tollens' test. Explain this observation.

Q10. What happens when sucrose is hydrolyzed? Name the products and the condition required for hydrolysis.

Q11. Why does starch give a blue colour with iodine while cellulose does not? Explain the structural basis.

Q12. Compare the branching in glycogen and amylopectin. Which one has more frequent branching and why?

Q13. (a) Describe the structure of sucrose. Explain why it is a non-reducing sugar despite being made of glucose and fructose, both of which are reducing sugars.

(b) Draw the Haworth structure of sucrose showing the glycosidic linkage.

(c) What happens when sucrose is treated with dilute acid or the enzyme invertase? Name the products and the mixture formed.

Q14. (a) Compare the structures of starch and cellulose. Explain why:

(i) Starch is digestible by humans but cellulose is not

(ii) Starch serves as food storage while cellulose serves as structural material

(b) Describe the composition and structure of glycogen. Why is it called 'animal starch'?

(c) A student eats a banana before a cricket match. Trace the conversion of starch from the banana to glycogen in his muscles, mentioning the key enzymes and processes involved.

Q15. (a) Fructose exists in both furanose and pyranose forms. Draw the Haworth projection of β-D-fructofuranose.

(b) Explain why fructose is sweeter than glucose and sucrose.

(c) When fructose is treated with dilute alkali, it undergoes Lobry de Bruyn-Alberda van Ekenstein transformation. What products are formed? Explain the significance of this reaction.

Q16. A sample of sucrose weighing 34.2 g is hydrolyzed completely.

(a) Write the balanced chemical equation for the hydrolysis of sucrose.

(b) Calculate the mass of glucose and fructose produced. (Molar mass of sucrose = 342 g/mol, glucose = 180 g/mol, fructose = 180 g/mol)

(c) The mixture obtained after hydrolysis is called 'invert sugar.' Why is it called so?

(d) This invert sugar is sweeter than the original sucrose. Explain why.

(e) If the hydrolysis is carried out using the enzyme invertase instead of acid, what advantage does this have in the food industry?

Q17. The following data compares three polysaccharides:

(a) Complete the table by filling in the correct information for each property.

(b) Calculate the approximate number of glucose units in a glycogen molecule if its molecular mass is about 10⁷ daltons. (Molecular mass of glucose unit = 162 g/mol, accounting for water loss during polymerization)

(c) A plant stores 500 g of starch. How many grams of glucose would be obtained upon complete hydrolysis?

(d) Why does cellulose have a higher tensile strength than starch? Explain in terms of molecular structure.

Q18. In India, jaggery (gur) is a traditional sweetener made from sugarcane juice. It contains sucrose, glucose, fructose, and minerals.

(a) When jaggery is dissolved in water and treated with Fehling's solution, a red precipitate forms. Explain why, considering the composition of jaggery.

(b) A sweet shop owner wants to test whether the jaggery he bought is pure or adulterated with starch. Which test would you suggest? Describe the procedure and expected observation.

(c) During the festival of Makar Sankranti, people eat tilgul (sesame and jaggery sweets). The sesame seeds contain oil, protein, and some carbohydrates. Which carbohydrate test would be positive for sesame seeds? Explain.

(d) A diabetic patient is advised to use stevia (a non-carbohydrate sweetener) instead of jaggery. Why is stevia a better option for diabetics compared to sucrose?

(e) The glycemic index (GI) measures how quickly a food raises blood glucose levels. Rank the following from lowest to highest GI: fructose, sucrose, glucose, starch. Explain your reasoning.