Chemistry Class 12 NCERT Solutions: Chapter 14 Biomolecules Part 2

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Exercise-2

Q: 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.

Q: 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.

Q: 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.

Q: 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

Q 4 Classification Of Carbohydrates

Q 4 Classification of Carbohydrates

Q 4 Classification Of Carbohydrates

Q: 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, and , are joined together by a glycosidic linkage.

Q 5 Structure of -D-Glucose and -D-Fructose, are Joined Glycosidic Linkage

Q 5 D-Glucose and -D-Fructose Joined Glycosidic Linkage

Q 5 Structure of -D-Glucose and -D-Fructose, are Joined Glycosidic Linkage

Q: 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 and amylopectin

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

Q: 7. What are the hydrolysis products of (i) sucrose and (ii) lactose?

Answer:

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

Q 7 i Structure of Sucrose

Q 7 I Structure of Sucrose

Q 7 i Structure of Sucrose

(ii) The hydrolysis of lactose gives and .

Q 7 ii Structure of Lactose

Q 7 Ii Structure of Lactose

Q 7 ii Structure of Lactose