Page No 423: - Chapter 14 Biomolecules Exercise Solutions class 12 ncert solutions Chemistry - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Question 14.1:

What are monosaccharides?

Answer:

Monosaccharides are carbohydrates that cannot be hydrolysed further to give simpler units of polyhydroxy aldehyde or ketone.

Monosaccharides are classified on the bases of number of carbon atoms and the functional group present in them. Monosaccharides containing an aldehyde group are known as aldoses and those containing a keto group are known as ketoses. Monosaccharides are further classified as trioses, tetroses, pentoses, hexoses, and heptoses according to the number of carbon atoms they contain. For example, a ketose containing 3 carbon atoms is called ketotriose and an aldose containing 3 carbon atoms is called aldotriose.

Question 14.2:

What are reducing sugars?

Answer:

Reducing sugars are carbohydrates that reduce Fehling’s solution and Tollen’s reagent. All monosaccharides and disaccharides, excluding sucrose, are reducing sugars.

Question 14.3:

Write two main functions of carbohydrates in plants.

Answer:

Two main functions of carbohydrates in plants are:

(i) Polysaccharides such as starch serve as storage molecules.

(ii) Cellulose, a polysaccharide, is used to build the cell wall.

Question 14.4:

Classify the following into monosaccharides and disaccharides.

Ribose, 2-deoxyribose, maltose, galactose, fructose and lactose

Answer:

Monosaccharides:

Ribose, 2-deoxyribose, galactose, fructose

Disaccharides:

Maltose, lactose

Question 14.5:

What do you understand by the term glycosidic linkage?

Answer:

Glycosidic linkage refers to the linkage formed between two monosaccharide units through an oxygen atom by the loss of a water molecule.

For example, in a sucrose molecule, two monosaccharide units, ∝-glucose and β-fructose, are joined together by a glycosidic linkage.

Question 14.6:

What is glycogen? How is it different from starch?

Answer:

Glycogen is a carbohydrate (polysaccharide). In animals, carbohydrates are stored as glycogen.

Starch is a carbohydrate consisting of two components − amylose (15 − 20%) and amylopectin (80 − 85%).

However, glycogen consists of only one component whose structure is similar to amylopectin. Also, glycogen is more branched than amylopectin.

Question 14.7:

What are the hydrolysis products of (i) sucrose and (ii) lactose?

Answer:

(i) On hydrolysis, sucrose gives one molecule of ∝-D glucose and one molecule of β- D-fructose.

(ii) The hydrolysis of lactose gives β-D-galactose and β-D-glucose.

Question 14.8:

What is the basic structural difference between starch and cellulose?

Answer:

Starch consists of two components − amylose and amylopectin. Amylose is a long linear chain of ∝−D−(+)−glucose units joined by C1−C4 glycosidic linkage (∝-link).

Amylopectin is a branched-chain polymer of ∝-D-glucose units, in which the chain is formed by C1−C4 glycosidic linkage and the branching occurs by C1−C6 glycosidic linkage.

On the other hand, cellulose is a straight-chain polysaccharide of β-D-glucose units joined by C1−C4 glycosidic linkage (β-link).

Question 14.9:

What happens when D-glucose is treated with the following reagents?

(i) HI (ii) Bromine water (iii) HNO₃

Answer:

(i) When D-glucose is heated with HI for a long time, n-hexane is formed.

(ii) When D-glucose is treated with Br₂ water, D- gluconic acid is produced.

(iii) On being treated with HNO₃, D-glucose get oxidised to give saccharic acid.