Chapter 9 of Class 11 Biology is Biomolecules. It covers the major chemical constituents of living cells: carbohydrates, proteins, lipids, nucleic acids, and enzymes. These Class 11 Biology Chapter 9 solutions are also useful as quick revision notes before exams.
Carbohydrates
Composed of C, H, O (general formula (CH₂O)n). Classified as monosaccharides (glucose, fructose), oligosaccharides (sucrose, lactose — 2-10 units), and polysaccharides (starch, cellulose, glycogen — many units). Primary energy source and structural component (cellulose in plant cell walls).
Proteins
Polymers of amino acids linked by peptide bonds. Have four levels of structure: primary (amino acid sequence), secondary (alpha helix/beta sheet), tertiary (3D folding), quaternary (multiple polypeptide subunits, e.g. haemoglobin).
Lipids
Heterogeneous group, largely insoluble in water. Include fatty acids, triglycerides (fats/oils, energy storage), phospholipids (membrane component), and steroids (e.g. cholesterol).
Nucleic Acids
Polymers of nucleotides (each = nitrogenous base + pentose sugar + phosphate group). DNA stores genetic information (deoxyribose sugar, bases A,T,G,C). RNA is involved in protein synthesis (ribose sugar, bases A,U,G,C).
Enzymes
Biological catalysts, almost all proteins, that speed up biochemical reactions by lowering activation energy without being consumed. Highly specific to their substrate (lock-and-key or induced fit model). Activity affected by temperature, pH, substrate concentration, and inhibitors.
Class 11 Biology Chapter 9 – Notes and Extra Questions
Along with these NCERT Solutions, students can also use the Class 11 Biology Chapter 9 Extra Questions and Class 11 Biology Chapter 9 Revision Notes for quick revision and extra practice.
