Question 10.1
What are monosaccharides?
Steps only
They cannot be broken into smaller carbohydrates by hydrolysis.
Answer
Examples: glucose, fructose.
CLASS 12 · CHEMISTRY · CHAPTER 10
Biomolecules
Simple answers to all 25 current end-of-chapter questions.
25 worked answersComplete chapter answers
25 worked answers · short steps first, explanations when you need them
Chapter 10 Exercises
Textbook pages 302–303
Question 10.2
What are reducing sugars?
Steps only
They reduce Tollens' or Fehling's reagent.
Answer
Glucose and maltose are examples.
Question 10.3
Write two main functions of carbohydrates in plants.
Steps only
Energy storage (starch) and structural support (cellulose).
Answer
Energy storage and cell-wall structure.
Question 10.4
Classify ribose, 2-deoxyribose, maltose, galactose, fructose and lactose as monosaccharides or disaccharides.
Steps only
Separate the single-unit sugars from the paired sugars.
Answer
Mono: ribose, 2-deoxyribose, galactose, fructose. Di: maltose, lactose.
Question 10.5
What is a glycosidic linkage?
Steps only
Two sugars join and release water.
Answer
The connecting C–O–C bond is the glycosidic linkage.
Question 10.6
What is glycogen? How is it different from starch?
Steps only
Both store glucose; glycogen is the animal form and is more branched.
Answer
Glycogen is the more highly branched storage carbohydrate of animals.
Question 10.7
What are the hydrolysis products of (i) sucrose and (ii) lactose?
Steps only
Break each disaccharide into its two monosaccharides.
Answer
Sucrose → glucose + fructose; lactose → glucose + galactose.
Question 10.8
What is the basic structural difference between starch and cellulose?
Steps only
The glucose form and glycosidic linkage differ.
Answer
Starch: α-glucose. Cellulose: β-glucose, β(1→4) links.
Question 10.9
What happens when D-glucose is treated with (i) HI, (ii) bromine water and (iii) HNO₃?
Steps only
HI reduces; bromine water oxidises the aldehyde; HNO₃ oxidises both ends.
Answer
n-Hexane; gluconic acid; saccharic acid.
Question 10.10
List reactions of D-glucose that cannot be explained by its open-chain structure.
Steps only
The α and β forms and mutarotation are key evidence for ring formation.
Answer
Glucose mainly has a cyclic hemiacetal structure.
Question 10.11
What are essential and non-essential amino acids? Give two examples of each.
Steps only
Essential amino acids must come from food; the body can make non-essential ones.
Answer
Examples: essential—valine, lysine; non-essential—glycine, alanine.
Question 10.12
Define (i) peptide linkage, (ii) primary structure and (iii) denaturation.
Steps only
Define the bond, sequence and shape change.
Answer
Peptide bond; amino-acid sequence; loss of natural shape/activity.
Question 10.13
What are the common types of secondary structure of proteins?
Steps only
These are regular folds stabilised by hydrogen bonds.
Answer
α-Helix and β-pleated sheet.
Question 10.14
What type of bonding stabilises the α-helix structure of proteins?
Steps only
Backbone peptide groups form hydrogen bonds.
Answer
Hydrogen bonds.
Question 10.15
Differentiate between globular and fibrous proteins.
Steps only
Compare shape, solubility and role.
Answer
Globular: compact, often soluble. Fibrous: long, usually insoluble and structural.
Question 10.16
How do amino acids show amphoteric behaviour?
Steps only
–COOH donates H⁺; –NH₂ accepts H⁺.
Answer
Amino acids are amphoteric.
Question 10.17
What are enzymes?
Steps only
They catalyse reactions in living systems.
Answer
Biological catalysts.
Question 10.18
What is the effect of denaturation on protein structure?
Steps only
The folded shape is disrupted; function is usually lost.
Answer
Secondary/tertiary structure changes; primary structure usually remains.
Question 10.19
How are vitamins classified? Name the vitamin responsible for blood coagulation.
Steps only
Group vitamins by solubility.
Answer
Fat-soluble A, D, E, K; water-soluble B, C. Clotting: K.
Question 10.20
Why are vitamins A and C essential? Give important sources.
Steps only
A: vision and tissue health. C: connective tissue and healing.
Answer
Sources: A—carrot, milk, eggs; C—citrus, amla, guava.
Question 10.21
What are nucleic acids? Mention two important functions.
Steps only
DNA and RNA are nucleotide polymers.
Answer
They carry genetic information and support protein synthesis.
Question 10.22
What is the difference between a nucleoside and a nucleotide?
Steps only
A nucleotide has phosphate; a nucleoside does not.
Answer
Base + sugar; base + sugar + phosphate.
Question 10.23
The two DNA strands are complementary, not identical. Explain.
Steps only
A pairs with T; G pairs with C.
Answer
The strands have matching complementary sequences.
Question 10.24
Give important structural and functional differences between DNA and RNA.
Steps only
Compare sugar, base, strands and role.
Answer
DNA stores hereditary information; RNA mainly helps protein synthesis.
Question 10.25
What are the different types of RNA found in a cell?
Steps only
Each type supports a different part of protein synthesis.
Answer
Messenger, transfer and ribosomal RNA.