CHAPTER-2

Question 1

Most abundant elements:

Answer 1

Hydrogen (H)

Carbon (C)

Oxygen (O)

Nitrogen (N)

Question 2

Importance of Carbon

Answer 2

Forms long chains or ring structures (organic molecules).

Acts as the “skeleton” for biological molecules.

Organic molecules always contain carbon (C) and hydrogen (H).

Question 3

Elements in Chemical Evolution Before Life

Answer 3

1 methane (CH4),
2 carbon dioxide (CO2),
3 hydrogen (H2),
4 water (H2O),
5 nitrogen (N2),
6 ammonia (NH3)
7 hydrogen sulfide (H2S), and an
energy source

Question 4

Types of Biological Molecules

Answer 4

Monosaccharides (simple sugars) → Polysaccharides (e.g., starch, cellulose).

Amino acids → Proteins.

Nucleotides → Nucleic acids (DNA/RNA).

Fatty acids + glycerol → Lipids (fats/oils).

Question 5

What are Macromolecules/ polymers

Answer 5

Giant molecules found in living organisms.
Polysaccharides (e.g., starch, cellulose)

Proteins (Polypeptides) (e.g., enzymes, hemoglobin)

Nucleic Acids (Polynucleotides) (e.g., DNA, RNA)

Question 6

Lipids

Answer 6

Made of fatty acids + glycerol.

Not true polymers (no repeating units).

Question 7

polymers made of

Answer 7

monomers

Question 8

Basics of Carbohydrates

Answer 8

Elements: Contain C, H, O (Carbon, Hydrogen, Oxygen)

Ratio: H:O = 2:1 (like water, H₂O → “hydrate” in the name)

General Formula: Cₓ(H₂O)ᵧ

Question 9

Classification of Carbohydrates

Answer 9

Monosaccharides
Disaccharides
Polysaccharides

Question 10

Monosaccharides

Answer 10

Simple sugars (single sugar unit)

Formula: (CH₂O)ₙ

Sweet, water-soluble

Question 11

Types of Monosaccharides by Carbon Number:

Answer 11

Trioses (3C)

Pentoses (5C) → Ribose, Deoxyribose (for DNA/RNA)

Hexoses (6C) → Glucose, Fructose, Galactose

Names end with “-ose” (e.g., glucose).

Question 12

Monomer

Answer 12

Small building block for synthesis of polymer

Question 13

Polymer

Answer 13

Large molecule made of repeating monomers (e.g., starch = many glucoses).

Question 14

Macromolecule

Answer 14

Giant biological polymer (e.g., proteins, polysaccharides, DNA).

Question 15

Isomers:

Answer 15

Same formula, different structure → different functions!

Question 16

Molecular vs. Structural Formula

Answer 16

Molecular Formula:

General representation of atoms (e.g., glucose = C₆H₁₂O₆).

Structural Formula:

Shows arrangement of atoms (e.g., glucose chain/ring forms).

Question 17

Glucose Structure

Answer 17

Hexose Sugar: 6-carbon monosaccharide (C₆H₁₂O₆).

Functional Groups:

Hydroxyl (–OH): Polar, makes glucose water-soluble.

Carbonyl (C=O): Reacts to form rings.

Question 18

Ring Formation

Answer 18

Why Rings?: More stable than linear chains.

Process:

Carbon-1 (C1) bonds with oxygen on C5.

Forms a 6-membered ring (5C + 1O).

C6 remains outside the ring.

Question 19

Alpha (α) vs. Beta (β) Glucose

Answer 19

Difference: Position of –OH on C1:

α-glucose: –OH below the ring.

β-glucose: –OH above the ring.

Question 20

Roles of Monosaccharides in Living Organisms

Answer 20

1. Energy Source
   Respiration: Broken down to release energy stored in C–H bonds.

ATP Production: Energy used to convert ADP + Pᵢ → ATP (cell’s energy currency).

Key Monosaccharide: Glucose (main fuel for cells).

2. Building Blocks for Larger Molecules
   Polysaccharides:

Starch/Glycogen (energy storage) ← glucose.

Cellulose (plant cell walls) ←glucose.

Nucleic Acids:

RNA & ATP ← Ribose (5C pentose).

DNA ← Deoxyribose (lacks one oxygen vs. ribose).

Question 21

. What are Disaccharides?

Answer 21

Double sugars formed by linking 2 monosaccharides

Formation: Via condensation reaction (removes H₂O, forms glycosidic bond)

Breakdown: Via hydrolysis (adds H₂O to split)

Question 22

Disaccharide Maltose

Answer 22

α-Glucose + α-Glucose

glycosidic bond is
formed between carbon atoms 1 and 4 of neighbouring glucose molecules

Question 23

Disaccharide Sucrose

Answer 23

α-glucose + β-fructose molecule.

Question 24

Disaccharide Lactose

Answer 24

Glucose + Galactose

Question 25

Glycosidic Bond Formation

Answer 25

–OH groups align on two monosaccharides. Condensation: One –OH loses H, the other loses –OH → forms H₂O. Remaining O bridges the sugars → glycosidic bond.

Question 26

Monosaccharide defenition

Answer 26

A monosaccharide is a molecule consisting of a single sugar unit with the general formula (CH2O)n.

Question 27

define disaccharide

Answer 27

A disaccharide is a sugar molecule consisting of two monosaccharides joined together by a glycosidic bond.

Question 28

define polysaccharide

Answer 28

A polysaccharide is a polymer whose subunits are monosaccharides joined together by glycosidic bonds

Question 29

The only common non-reducing sugar is

Answer 29

sucrose

Question 30

Starch (Plant Storage)

Answer 30

Mixture of amylose + amylopectin. Found in: Chloroplasts, potatoes, grains. Test: Iodine → blue-black. Insoluble → No osmotic effect.

Question 31

Amylose

Answer 31

Structure: Linear α-glucose chain (α1→4 bonds). Coils into helix → Compact storage. Digests slower (unbranched).

Question 32

Amylopectin

Answer 32

Structure: Branched α-glucose (α1→4 + α1→6 bonds). Branches → Faster digestion (more enzyme sites). Major starch component (~70-80%).

Question 33

Glycogen (Animal Storage)

Answer 33

Structure: More branched than amylopectin (α1→4 + many α1→6). Found in: Liver/muscles (granules). Function: Rapid energy release (highly branched).

Question 34

Cellulose

Answer 34

1. Basic Structure Polymer of β-glucose (differs from starch/glycogen which use α-glucose). β(1→4) glycosidic bonds: Each glucose flips 180° → forms straight, unbranched chains. 2. Hydrogen Bonding Within chains: –OH groups form H-bonds with O atoms in the same chain. Between chains: H-bonds link parallel cellulose molecules → microfibrils (bundles of 60–70 chains). Microfibrils → fibres → layered in cell walls for strength. 3. Mechanical Strength Tensile strength ≈ steel (resists stretching/breaking). Functions: Prevents cell bursting under osmotic pressure. Provides rigidity to plant tissues. Guides cell shape during growth. 4. Cell Wall Composition 20–40% cellulose + other molecules (e.g., hemicellulose, pectin) for cross-linking. Fibres arranged in layers (different directions → maximizes strength). 5. Permeability Despite strength, freely permeable to water/solutes (unlike lignin-reinforced walls).

Question 35

Why β-Glucose Matters:

Answer 35

Straight chains → H-bond networks → strength (vs. coiled α-glucose in starch).

Question 36

cell wall flow chart

Answer 36

β-Glucose → β(1→4) bond → Straight chain → H-bonds → parallel chain→ Microfibril →cellulose Fibre → Cell wall

Question 37

Dipoles (Polar Covalent Bonds)

Answer 37

Unequal electron sharing in covalent bonds → partial charges (δ⁺/δ⁻). Example (H₂O): Oxygen (δ⁻) attracts electrons more than hydrogen (δ⁺).

Question 38

Hydrogen Bonds

Answer 38

Attraction between δ⁺ (H) and δ⁻ (O/N/F) of different molecules. Strength: Weaker than covalent bonds but crucial biologically. Example: Links water molecules → high surface tension/cohesion.

Question 39

Key Groups Forming H-Bonds

Answer 39

–OH → Hydroxyl →In carbs (cellulose), alcohols –CO →Carbonyl →In proteins/sugars –NH→ Amine → In proteins/nucleic acids

Question 40

Hydrophilic vs. Hydrophobic

Answer 40

Hydrophilic (Polar) Hydrophobic (Non-polar)

Question 41

Lipids

Answer 41

Organic molecules insoluble in water (hydrophobic). True lipids = Fatty acids + Alcohol (glycerol) → Esters.

Question 42

Fatty Acids

Answer 42

Head: Carboxyl group (–COOH) → polar/"acidic" Tail: Hydrocarbon chain (15-17 C atoms) → non-polar

Question 43

Fatty Acids Types

Answer 43

Unsaturated fats: C=C bonds introduce kinks → lower melting point (oils). they do not contain the maximum possible amount of hydrogen Healthier (reduce LDL cholesterol). Saturated fats: Straight chains pack tightly → higher melting point (solids). Linked to cardiovascular disease.

Question 44

Unsaturated fatty acids

Answer 44

Monounsaturated - 1 C=C bond Liquid (oils) - Olive oil, nuts Polyunsaturated - 2+ C=C bonds Liquid (oils) - Fish, sunflower oil

Question 45

Alcohols

Answer 45

Definition: Organic molecules with –OH group attached to carbon. Example: Glycerol (3 –OH groups) → Key in lipid formation.

Question 46

Esters & Ester Bonds

Answer 46

Formation: Acid (–COOH) + Alcohol (–OH) → Ester (–COO–) + H₂O (condensation). Ester Bond: –COO– linkage (holds fatty acids to glycerol in lipids). Reverse Reaction: Hydrolysis (ester + H₂O → acid + alcohol).

Question 47

Triglyceride Formation

Answer 47

Triglyceride Formation: 3 Fatty Acids + Glycerol ↓ (Condensation; removes 3H₂O) Triglyceride (3 ester bonds) ↓ (Hydrolysis; adds 3H₂O) Back to fatty acids + glycerol

Question 48

Phospholipids

Answer 48

Head: Phosphate group (-PO₄) → hydrophilic (water-loving, polar). Tails: 2 Fatty acid chains → hydrophobic (water-hating, non-polar). This allows the molecules to form a membrane around a cell, where the hydrophilc heads lie in the watery solutions on the outside of the membrane, and the hydrophobic tails form a layer that is impermeable to hydrophilic substances.

Question 49

Amino Acids

Answer 49

H | H₂N–C–COOH | R Central (α) Carbon: Bonded to: Amino group (–NH₂) Carboxyl group (–COOH) Hydrogen (–H) Variable R group (side chain) → Determines amino acid type.