Chapter 9: Biomolecules – Short Answer Type Questions

CBSE Class 11 Biology Short Answer Questions – Biomolecules (Chapter 9 | NCERT)

Course: CBSE Class 11 Biology
Unit III: Cell Structure and Function
Chapter 9: Biomolecules
Based on: NCERT Syllabus
Examination: CBSE Board Examinations (Class XI)

🔹 CBSE Class 11 Biology Chapter 9 Biomolecules: 50 Short Answer Questions with NCERT-Based Answers

Section A: Carbohydrates (Q1–Q8)

Q1. What are carbohydrates? Explain their general formula and biological role.
Answer:
Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, usually in the ratio (CH₂O)ₙ. They serve as primary energy sources, structural components, and storage molecules in living organisms, especially in plants and animals.

Q2. Differentiate between monosaccharides and polysaccharides.
Answer:
Monosaccharides are simple sugars that cannot be hydrolysed further, such as glucose and fructose. Polysaccharides are complex carbohydrates made of many monosaccharide units linked by glycosidic bonds, such as starch and cellulose.

Q3. What is the structural difference between glucose and fructose?
Answer:
Glucose is an aldohexose containing an aldehyde group, whereas fructose is a ketohexose containing a ketone group. Though both have the same molecular formula (C₆H₁₂O₆), their functional groups differ.

Q4. Explain glycosidic linkage with an example.
Answer:
A glycosidic linkage is a covalent bond formed between two monosaccharides through a dehydration reaction. For example, in sucrose, glucose and fructose are linked by an α,β-1,2 glycosidic bond.

Q5. Distinguish between starch and cellulose.
Answer:
Starch is a storage polysaccharide in plants made of α-glucose units, while cellulose is a structural polysaccharide composed of β-glucose units. Humans can digest starch but not cellulose.

Q6. What is chitin? Mention its significance.
Answer:
Chitin is a nitrogen-containing polysaccharide composed of N-acetylglucosamine units. It forms the exoskeleton of arthropods and provides structural strength to fungal cell walls.

Q7. Why are carbohydrates called reducing sugars?
Answer:
Carbohydrates containing a free aldehyde or ketone group can donate electrons and reduce other substances. Such sugars are called reducing sugars, for example, glucose and maltose.

Q8. What is the biological importance of cellulose?
Answer:
Cellulose provides mechanical strength to plant cell walls. It maintains cell shape, protects internal structures, and contributes to dietary fiber in humans, aiding digestion.

Section B: Proteins (Q9–Q18)

Q9. Define proteins and mention their basic building blocks.
Answer:
Proteins are polymers of amino acids linked by peptide bonds. They are essential biomolecules involved in structural support, enzymatic activity, transport, regulation, and defense in living organisms.

Q10. What is an amino acid? Describe its general structure.
Answer:
An amino acid is an organic compound containing both an amino group (–NH₂) and a carboxyl group (–COOH). A central carbon is attached to hydrogen, an amino group, a carboxyl group, and a variable side chain.

Q11. What are peptide bonds? How are they formed?
Answer:
A peptide bond is formed between the carboxyl group of one amino acid and the amino group of another through a condensation reaction, releasing a molecule of water.

Q12. Explain primary structure of proteins.
Answer:
The primary structure of a protein refers to the specific linear sequence of amino acids linked by peptide bonds. This sequence determines the protein’s overall structure and biological function.

Q13. Distinguish between fibrous and globular proteins.
Answer:
Fibrous proteins are elongated, insoluble, and provide structural support, such as keratin. Globular proteins are compact, soluble, and perform metabolic functions, such as enzymes and hormones.

Q14. What is protein denaturation?
Answer:
Protein denaturation is the loss of secondary and tertiary structure due to heat, pH change, or chemicals. This results in loss of biological activity without breaking peptide bonds.

Q15. Explain the significance of tertiary structure of proteins.
Answer:
The tertiary structure determines the three-dimensional folding of a protein, essential for its biological activity. It is stabilized by hydrogen bonds, ionic bonds, and disulfide linkages.

Q16. What are essential amino acids?
Answer:
Essential amino acids cannot be synthesized by the human body and must be obtained through diet. Examples include lysine, methionine, and tryptophan.

Q17. Why are proteins called polypeptides?
Answer:
Proteins consist of long chains of amino acids linked by peptide bonds. Since they contain multiple peptide linkages, they are termed polypeptides.

Q18. Mention any two functions of proteins in living cells.
Answer:
Proteins act as enzymes to catalyze biochemical reactions and as structural components like collagen. They also function in transport, immunity, and regulation.

Section C: Lipids (Q19–Q25)

Q19. Define lipids and mention their general characteristics.
Answer:
Lipids are hydrophobic organic molecules insoluble in water but soluble in organic solvents. They include fats, oils, phospholipids, and steroids, serving as energy reserves and membrane components.

Q20. What are triglycerides?
Answer:
Triglycerides are lipids formed by the esterification of one glycerol molecule with three fatty acids. They act as major energy storage molecules in animals and plants.

Q21. Differentiate between saturated and unsaturated fatty acids.
Answer:
Saturated fatty acids contain no double bonds and are solid at room temperature, whereas unsaturated fatty acids have one or more double bonds and are usually liquid.

Q22. What is the role of phospholipids in cells?
Answer:
Phospholipids form the basic structural framework of cell membranes. Their amphipathic nature allows formation of bilayers essential for membrane fluidity and permeability.

Q23. Explain the significance of cholesterol.
Answer:
Cholesterol stabilizes animal cell membranes and serves as a precursor for steroid hormones, bile acids, and vitamin D.

Q24. Why are lipids considered high-energy molecules?
Answer:
Lipids yield more energy per gram than carbohydrates due to their high number of carbon-hydrogen bonds, making them efficient long-term energy storage molecules.

Q25. What are waxes? Mention one function.
Answer:
Waxes are esters of long-chain fatty acids and alcohols. They provide waterproofing and protection to plant surfaces and animal skin.

Section D: Nucleic Acids (Q26–Q34)

Q26. What are nucleic acids?
Answer:
Nucleic acids are polymers of nucleotides responsible for storage and transmission of genetic information. The two main types are DNA and RNA.

Q27. Describe the structure of a nucleotide.
Answer:
A nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group. These units polymerize to form nucleic acids.

Q28. Differentiate between DNA and RNA.
Answer:
DNA contains deoxyribose sugar and thymine, while RNA contains ribose sugar and uracil. DNA is double-stranded, whereas RNA is usually single-stranded.

Q29. What is a phosphodiester bond?
Answer:
A phosphodiester bond links adjacent nucleotides by joining the phosphate group of one nucleotide to the sugar of another, forming the nucleic acid backbone.

Q30. Explain the significance of complementary base pairing.
Answer:
Complementary base pairing ensures accurate DNA replication and transcription. Adenine pairs with thymine, and guanine pairs with cytosine via hydrogen bonds.

Q31. What is the role of RNA in protein synthesis?
Answer:
RNA acts as a messenger carrying genetic information from DNA to ribosomes and assists in assembling amino acids into proteins.

Q32. Define genome.
Answer:
A genome is the complete set of genetic material present in an organism, stored primarily in DNA molecules.

Q33. What are purines and pyrimidines?
Answer:
Purines are double-ring nitrogenous bases like adenine and guanine, while pyrimidines are single-ring bases like cytosine, thymine, and uracil.

Q34. Mention one biological role of DNA.
Answer:
DNA stores hereditary information and ensures its transmission from one generation to the next.

Section E: Enzymes & Metabolism (Q35–Q50)

Q35. Define enzymes.
Answer:
Enzymes are biological catalysts, mostly proteins, that speed up biochemical reactions without being consumed in the process.

Q36. Explain the specificity of enzymes.
Answer:
Enzymes are highly specific due to the unique shape of their active site, which binds only to a particular substrate.

Q37. What is an active site?
Answer:
The active site is a specific region of an enzyme where the substrate binds and the catalytic reaction occurs.

Q38. Describe the lock-and-key model.
Answer:
This model suggests that the substrate fits exactly into the enzyme’s active site, similar to a key fitting into a lock.

Q39. What is enzyme denaturation?
Answer:
Enzyme denaturation involves loss of three-dimensional structure due to extreme temperature or pH, resulting in loss of catalytic activity.

Q40. Define metabolism.
Answer:
Metabolism is the sum total of all biochemical reactions occurring in a living organism, maintaining life processes.

Q41. Differentiate between anabolism and catabolism.
Answer:
Anabolism involves synthesis of complex molecules requiring energy, while catabolism involves breakdown of molecules releasing energy.

Q42. What is ATP? Why is it important?
Answer:
ATP is the energy currency of the cell, providing energy for metabolic reactions, transport, and cellular activities.

Q43. Explain the role of enzymes in metabolism.
Answer:
Enzymes regulate metabolic pathways by catalyzing specific reactions, ensuring efficiency and control of cellular processes.

Q44. What are coenzymes?
Answer:
Coenzymes are organic, non-protein molecules that assist enzymes during catalysis, often derived from vitamins.

Q45. How does temperature affect enzyme activity?
Answer:
Enzyme activity increases with temperature up to an optimum level, beyond which denaturation occurs, reducing activity.

Q46. Explain the effect of pH on enzymes.
Answer:
Each enzyme has an optimum pH. Deviations from this pH alter enzyme structure and reduce catalytic efficiency.

Q47. What are isoenzymes?
Answer:
Isoenzymes are different molecular forms of the same enzyme that catalyze identical reactions but differ in structure.

Q48. Define metabolic pathway.
Answer:
A metabolic pathway is a sequence of enzyme-catalyzed reactions leading to the synthesis or breakdown of biomolecules.

Q49. What is feedback inhibition?
Answer:
Feedback inhibition is a regulatory mechanism where the end product of a pathway inhibits an earlier enzyme, controlling metabolic flow.

Q50. Why is metabolism essential for living organisms?
Answer:
Metabolism provides energy, synthesizes essential biomolecules, and maintains cellular organization, ensuring survival and growth.