Exercise Chapter 2: Biological Molecules Class 11
MCQs with answers from Chapter 2 : Biological Molecules (Federal Board, 11th Class):
MCQs – Biological Molecules
1. An amino acid molecule has the following structure:
Which two groups combine to form a peptide link between two amino acids?(A) 1 and 2
(B) 1 and 3
(C) 2 and 3
(D) 2 and 4
✅ Answer: (C) 2 and 3
2. Which class of molecule is the major component of the cell membrane?
(A) Phospholipid(B) Cellulose
(C) Wax
(D) Triglyceride
✅ Answer: (A) Phospholipid
3. Glycerol is the backbone molecule for:
(A) ATP(B) Terpenes
(C) Neutral lipids
(D) Steroids
✅ Answer: (C) Neutral lipids
4. A fatty acid is unsaturated if it:
(A) Contains hydrogen(B) Contains double bonds
(C) Contains an acid group
(D) All of them
✅ Answer: (B) Contains double bonds
5. In RNA, the nitrogen base that takes the place of thymine is:
(A) Adenine(B) Cytosine
(C) Guanine
(D) Uracil
✅ Answer: (D) Uracil
6. The ending "-ose" means a substance is a:
(A) Sugar(B) Lipid
(C) Protein
(D) Nucleic acid
✅ Answer: (A) Sugar
7. Glycolipids and lipoproteins are important components of:
(A) Cellular membrane(B) Cell wall
(C) Both of them
(D) None of them
✅ Answer: (A) Cellular membrane
8. When two amino acids are linked to form a peptide bond, what is removed?
(A) Hydroxyl (-OH)(B) Water (H₂O)
(C) Carbon (C)
(D) Nitrogen (N)
✅ Answer: (B) Water (H₂O)
9. What is the theoretical number of chemically different dipeptides that may be assembled from two amino acids?
(A) One(B) Two
(C) Three
(D) Four
✅ Answer: (D) Four
10. A polar molecule is ________ in water.
(A) Soluble(B) Insoluble
(C) Reactive
(D) Inert
✅ Answer: (A) Soluble
11. Which statement correctly describes a property of water?
(A) A relatively large amount of heat is needed to increase its temperature.(B) At normal room temperature, its molecules are bound together by ionic bonds.
(C) The highest density of water occurs below its freezing point.
(D) Water acts as a solvent for non-polar molecules.
✅ Answer: (A) A relatively large amount of heat is needed to increase its temperature.
12. Estrogen, Vitamin-D, and cholesterol are all examples of:
(A) Glycolipids(B) Lipoproteins
(C) Terpenes
(D) Steroids
✅ Answer: (D) Steroids
13. Which term includes all others?
(A) Carbohydrate(B) Starch
(C) Monosaccharide
(D) Polysaccharide
✅ Answer: (A) Carbohydrate
14. Choose the pair of terms that correctly completes this sentence: Nucleotides are to nucleic acids as ________ are to proteins.
(A) Nucleic acids; Amino acids(B) Amino acids; Polypeptides
(C) Glycosidic linkages; Polypeptide linkages
(D) Polymers; Polypeptides
✅ Answer: (B) Amino acids; Polypeptides
15. The enantiomer of D-glucose is:
(A) D-galactose(B) L-galactose
(C) Both of them
(D) None of them
✅ Answer: (D) None of them
Short Questions with answers from Chapter 2: Biological Molecules (Federal Board, 11th Class):
Short Questions – Biological Molecules
Short Questions with Answers
2️⃣ How would you describe biochemistry?
✅ Answer: Biochemistry is the branch of science that studies the chemical composition and reactions of biomolecules in living organisms. It includes the study of proteins, carbohydrates, lipids, nucleic acids, and the processes like metabolism, enzyme activity, and genetic regulation.3️⃣ What are bioelements?
✅ Answer: Bioelements are chemical elements essential for the structure and function of living organisms. They are categorized into:✔ Major bioelements (99%) – Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sulfur (S).
✔ Minor bioelements (<1%) – Calcium (Ca), Potassium (K), Sodium (Na), Chlorine (Cl), Magnesium (Mg).
✔ Trace elements (<0.01%) – Iron (Fe), Copper (Cu), Zinc (Zn), Manganese (Mn), Iodine (I).
4️⃣ Describe the chemical composition of protoplasm.
✅ Answer: Protoplasm is the living content of a cell, composed of:✔ Water (70-80%) – Acts as a solvent & medium for biochemical reactions.
✔ Proteins (15-18%) – Structural & enzymatic functions.
✔ Carbohydrates (3-4%) – Energy source.
✔ Lipids (2-3%) – Energy storage, membrane structure.
✔ Nucleic Acids (DNA & RNA) – Genetic information & protein synthesis.
✔ Inorganic Ions (Na⁺, K⁺, Cl⁻, Mg²⁺, Ca²⁺) – Maintain cellular function.
5️⃣ What are the four fundamental kinds of biological molecules? Explain.
✅ Answer: The four fundamental biological molecules are:✔ Carbohydrates – Made of C, H, O; provide energy & structural support (e.g., glucose, starch, cellulose).
✔ Proteins – Made of amino acids; function in enzymes, hormones, transport, and structure (e.g., hemoglobin, enzymes).
✔ Lipids – Made of fatty acids & glycerol; used for energy storage, insulation, and cell membranes (e.g., triglycerides, phospholipids).
✔ Nucleic Acids – Made of nucleotides; store & transmit genetic information (e.g., DNA, RNA).
6️⃣ Why is the covalent bond in water polar?
✅ Answer: The covalent bond in water (H₂O) is polar because:✔ Oxygen is more electronegative than hydrogen, attracting electrons more strongly.
✔ This creates a partial negative charge (δ⁻) on oxygen and partial positive charges (δ⁺) on hydrogen, resulting in a dipole moment.
✔ This polarity allows water to form hydrogen bonds and act as a universal solvent.
7️⃣ Why is water regarded as a universal solvent?
✅ Answer: Water is called the universal solvent because:✔ It dissolves many substances due to its polarity.
✔ Ionic compounds (e.g., NaCl) dissolve as water separates their ions.
✔ Polar covalent molecules (e.g., sugars, proteins) dissolve via hydrogen bonding.
✔ This property allows water to transport nutrients, remove waste, and support biochemical reactions in living organisms.
8️⃣ What is the importance of hydrogen bonding?
✅ Answer: Hydrogen bonding plays a crucial role in biological systems by:✔ Stabilizing DNA – Holds base pairs (A=T, G≡C) together.
✔ Maintaining protein structure – Forms secondary & tertiary protein structures.
✔ Giving water unique properties – High cohesion, surface tension, and heat capacity.
✔ Supporting cellular function – Helps in enzyme-substrate binding and membrane integrity.
9️⃣ Why does a very large amount of heat increase the temperature of water only slightly?
✅ Answer: Water has a high specific heat capacity (4.18 J/g°C), meaning:✔ A large amount of heat is needed to break hydrogen bonds before raising the temperature.
✔ This property allows cells & aquatic environments to maintain stable temperatures, protecting organisms from sudden temperature changes.
🔟 How does water protect living things against sudden thermal change?
✅ Answer: Water has a high specific heat capacity, meaning it absorbs and releases heat slowly. This helps:✔ Maintain body temperature in living organisms.
✔ Protect aquatic life from extreme temperature fluctuations.
✔ Ensure enzyme stability, preventing protein denaturation.
1️⃣1️⃣ What is the importance of high heat of vaporization of water to animals?
✅ Answer: Water has a high heat of vaporization (574 cal/g), which helps:✔ Cooling through evaporation – Sweating and panting remove excess body heat.
✔ Temperature regulation – Heat is absorbed before evaporation, stabilizing body temperature.
✔ Prevent dehydration – Slow evaporation rate conserves water in desert animals.
1️⃣2️⃣ Describe the classification of carbohydrates.
✅ Answer: Carbohydrates are classified into:✔ Monosaccharides – Single sugar units (Glucose, Fructose).
✔ Disaccharides – Two monosaccharides linked by a glycosidic bond (Sucrose, Maltose, Lactose).
✔ Polysaccharides – Long chains of monosaccharides (Starch, Glycogen, Cellulose).
1️⃣3️⃣ Describe the classification of monosaccharides.
✅ Answer: Monosaccharides are classified based on:✔ Number of Carbon Atoms:
- Trioses (3C) – Glyceraldehyde.
- Pentoses (5C) – Ribose, Deoxyribose.
- Hexoses (6C) – Glucose, Fructose.
✔ Functional Group: - Aldoses – Contain an aldehyde (-CHO) group (e.g., Glucose).
- Ketoses – Contain a ketone (-CO) group (e.g., Fructose).
1️⃣4️⃣ Describe the conversion of open-chain ribose into a ring chain.
✅ Answer:✔ Ribose (a pentose sugar) exists in an open-chain form in dry state.
✔ In an aqueous solution, the -OH on C4 attacks the carbonyl carbon (C1), forming a furanose (5-membered) ring.
✔ This process is called intramolecular cyclization, creating α-ribose and β-ribose.
1️⃣5️⃣ Draw and label the ring forms of alpha and beta glucose.
✅ Answer:✔ α-Glucose – The -OH on C1 is below the ring.
✔ β-Glucose – The -OH on C1 is above the ring.
✔ Both exist in pyranose (6-membered) ring form in solutions.
1️⃣6️⃣ Justify that the laboratory-manufactured sweeteners are 'left-handed' sugars and cannot be metabolized by 'right-handed' enzymes.
✅ Answer:✔ Natural sugars are D-form (right-handed) and fit into enzyme active sites.
✔ Artificial sweeteners are L-form (left-handed), making them unrecognizable by digestive enzymes.
✔ Since enzymes are stereospecific, they cannot metabolize L-sugars, making them calorie-free.
1️⃣7️⃣ Illustrate the formation and breakage of:
✅ (a) Sucrose (b) Maltose (c) Lactose✔ Formation – Disaccharides form via condensation (dehydration synthesis), where a glycosidic bond is formed, and a water molecule (H₂O) is removed.
✔ Breakage – Disaccharides are broken by hydrolysis, where water is added, breaking the glycosidic bond.
| Disaccharide | Monosaccharides | Bond Type | Formation Process |
|---|---|---|---|
| Sucrose | Glucose + Fructose | α-1,2-glycosidic | Condensation |
| Maltose | Glucose + Glucose | α-1,4-glycosidic | Condensation |
| Lactose | Glucose + Galactose | β-1,4-glycosidic | Condensation |
1️⃣8️⃣ Draw the structural formula of an amino acid.
✅ Answer:✔ General structure of an amino acid:
✔ Components:
- Amino group (-NH₂)
- Carboxyl group (-COOH)
- Hydrogen atom (H)
- Variable R group (Side chain) – determines amino acid type
1️⃣9️⃣ Describe the synthesis of a peptide bond.
✅ Answer:✔ A peptide bond is formed between the carboxyl (-COOH) group of one amino acid and the amino (-NH₂) group of another.
✔ Condensation reaction removes H₂O to form a -CO-NH- (peptide bond).
✔ Example: Two amino acids forming a dipeptide.
2️⃣0️⃣ Describe the four types of protein structure
✅ Answer:| Level | Description | Example |
|---|---|---|
| Primary | Linear sequence of amino acids | Insulin |
| Secondary | Folding into α-helix or β-pleated sheet due to hydrogen bonding | Keratin, Silk |
| Tertiary | 3D structure formed by disulfide, ionic, hydrogen bonds | Enzymes, Myoglobin |
| Quaternary | Two or more polypeptides form a functional protein | Hemoglobin, Collagen |
2️⃣1️⃣ Describe:
✅ (a) Globular proteins
✔ Spherical, water-soluble, and functional proteins (e.g., enzymes, hemoglobin).✅ (b) Fibrous proteins
✔ Long, insoluble, and structural proteins (e.g., collagen, keratin).2️⃣2️⃣ Describe the classification of lipids.
✅ Answer: Lipids are classified into:| Type | Examples | Function |
|---|---|---|
| Simple Lipids | Triglycerides | Energy storage |
| Compound Lipids | Phospholipids, Glycolipids | Membrane structure |
| Derived Lipids | Steroids, Vitamins | Hormones, signaling |
2️⃣3️⃣ What role do lipids play in living organisms?
✅ Answer:✔ Energy storage – Provides 2× more energy than carbohydrates.
✔ Membrane formation – Phospholipids form cell membranes.
✔ Insulation & Protection – Fat stores insulate and cushion organs.
✔ Signaling molecules – Steroids regulate physiological functions.
2️⃣4️⃣ Why do phospholipids form a thin layer on the surface of an aqueous solution?
✅ Answer:✔ Phospholipids are amphipathic – They have a hydrophilic (polar) head and hydrophobic (non-polar) tails.
✔ In water, they arrange in a monolayer with hydrophilic heads facing water and hydrophobic tails avoiding water.
2️⃣5️⃣ What is an isoprene unit? Explain.
✅ Answer:✔ Isoprene unit (C₅H₈) is the basic building block of terpenes, steroids, and fat-soluble vitamins.
✔ Five-carbon structure that polymerizes to form natural rubber, carotenoids, and cholesterol precursors.
2️⃣6️⃣ Describe a steroid nucleus.
✅ Answer:✔ A steroid nucleus is a four-ringed hydrocarbon structure (three 6-membered rings and one 5-membered ring).
✔ It is found in cholesterol, steroid hormones (testosterone, estrogen), and vitamin D.
✔ Steroids are hydrophobic and play key roles in membrane stability, signaling, and metabolism.
2️⃣7️⃣ How might an error in the DNA of an organism affect protein function?
✅ Answer:✔ A mutation in DNA can change the amino acid sequence of a protein.
✔ This may result in:
- Loss of function (e.g., sickle cell anemia due to a single amino acid change in hemoglobin).
- Reduced enzyme activity or misfolded proteins.
- Defective cell signaling, leading to diseases (e.g., cancer).
2️⃣8️⃣ Define a gene.
✅ Answer: A gene is a specific sequence of nucleotides in DNA that codes for the synthesis of a polypeptide or functional RNA.✔ Genes determine traits, enzyme production, and cell functions.
✔ They follow the Central Dogma: DNA → RNA → Protein.
2️⃣9️⃣ Write the differences between:
✅ (a) Major and Minor Bioelements
✔ Major (99%) – C, H, O, N, P, S (found in macromolecules).
✔ Minor (<1%) – Ca, K, Na, Cl, Mg (used in nerve signaling, bones).
✅ (b) Dimer and Polymer
✔ Dimer – Two monomers linked (e.g., Maltose = Glucose + Glucose).
✔ Polymer – Many monomers linked (e.g., Starch, Proteins, DNA).
✅ (c) Polar and Non-Polar Covalent Bonds
✔ Polar – Unequal sharing of electrons (e.g., H₂O).
✔ Non-Polar – Equal sharing of electrons (e.g., O₂, CH₄).
✅ (d) Polyhydroxy Aldehyde and Polyhydroxy Ketone
✔ Aldehyde (-CHO) group in aldoses (e.g., Glucose).
✔ Ketone (-CO) group in ketoses (e.g., Fructose).
✅ (e) Alpha and Beta Glucose
✔ Alpha (α) Glucose – -OH on C1 is below the plane.
✔ Beta (β) Glucose – -OH on C1 is above the plane.
✅ (f) D-Glucose and L-Glucose
✔ D-Glucose – Found in nature, digestible by humans.
✔ L-Glucose – Synthetic, not metabolized by enzymes.
✅ (g) Amylose and Amylopectin
✔ Amylose – Linear, unbranched starch (α-1,4 bonds).
✔ Amylopectin – Branched starch (α-1,4 and α-1,6 bonds).
✅ (h) Amylopectin and Glycogen
✔ Amylopectin – Less branched, found in plants.
✔ Glycogen – Highly branched, stored in liver and muscles.
✅ (i) Primary and Secondary Structure of Proteins
✔ Primary – Linear sequence of amino acids.
✔ Secondary – Folding into α-helix or β-sheet (H-bonding).
✅ (j) Tertiary and Quaternary Structure of Proteins
✔ Tertiary – 3D folding due to disulfide & ionic bonds.
✔ Quaternary – Two or more polypeptides form a functional protein (e.g., Hemoglobin).
✅ (k) Purines and Pyrimidines
✔ Purines – Double-ringed bases (Adenine, Guanine).
✔ Pyrimidines – Single-ringed bases (Cytosine, Thymine, Uracil).
✅ (l) Saturated and Unsaturated Fatty Acids
✔ Saturated – No double bonds, solid at room temp (Butter).
✔ Unsaturated – Has double bonds, liquid at room temp (Olive oil).
✅ (m) DNA and RNA
✔ DNA – Double-stranded, stores genetic information.
✔ RNA – Single-stranded, helps in protein synthesis.
