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Biomolecules

NCERT Class 11 Biology Chapter 9

Biomolecules for Class 11 Biology and NEET: chemical composition of cells, proteins, carbohydrates, lipids and nucleic acids, and how enzymes work.

8 topics Updated 8 Nov 2026

For: Class 11 and NEET

In the syllabus: NEET Class 11 syllabus

With your textbook

NCERT Biology (Class 11), Chapter 9 “Biomolecules”, reprint 2026-27.

Open the official NCERT chapter (PDF, 1.9 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. How to analyse chemical composition

    How to analyse chemical composition for Class 11 Biology and NEET: acid-soluble pool, ash, amino acids and zwitterions, lipids, nucleosides vs nucleotides.

    NCERT Section 9.1 13 min read 6 solved examples 8 practice questions

  2. Primary and secondary metabolites

    Primary and secondary metabolites for Class 11 Biology and NEET: their difference, uses to people, and the classes and examples in NCERT Table 9.3.

    NCERT Section 9.2 7 min read 3 solved examples 6 practice questions

  3. Biomacromolecules

    Biomacromolecules for Class 11 Biology and NEET: micromolecules and macromolecules, why lipids are in the acid-insoluble fraction, and cell composition.

    NCERT Section 9.3 7 min read 4 solved examples 6 practice questions

  4. Proteins

    Proteins for Class 11 Biology and NEET: polypeptides as heteropolymers, essential and non-essential amino acids, protein functions, collagen and RuBisCO.

    NCERT Section 9.4 7 min read 4 solved examples 6 practice questions

  5. Polysaccharides

    Polysaccharides for Class 11 Biology and NEET: starch vs cellulose vs glycogen, a glycogen diagram, inulin, reducing ends, the iodine test and chitin.

    NCERT Section 9.5 8 min read 4 solved examples 6 practice questions

  6. Nucleic acids

    Nucleic acids for Class 11 Biology and NEET: nucleotides of base, sugar and phosphate, purines and pyrimidines, and how DNA and RNA differ by sugar.

    NCERT Section 9.6 6 min read 4 solved examples 6 practice questions

  7. Structure of proteins

    Structure of proteins for Class 11 Biology and NEET: the four levels of protein structure, primary to quaternary, with a labelled diagram and haemoglobin.

    NCERT Section 9.7 8 min read 3 solved examples 6 practice questions

  8. Enzymes

    Enzymes for Class 11 Biology and NEET: how they work, activation energy, factors affecting activity, competitive inhibition, six classes and co-factors.

    NCERT Section 9.8 16 min read 5 solved examples 9 practice questions

Key formulas in this chapter

Chemical composition

  • grinding agent: trichloroacetic acid (ClCCOOH)
  • filtrate: acid-soluble pool; retentate: acid-insoluble fraction
  • amino acid: α-carbon with H, –COOH, –NH and R
  • palmitic acid: 16 carbons; arachidonic acid: 20 carbons
  • nucleoside: base + sugar; nucleotide: base + sugar + phosphate

Primary and secondary metabolites

  • alkaloids: morphine, codeine
  • toxins: abrin, ricin
  • lectins: concanavalin A
  • drugs: vinblastine, curcumin
  • polymeric substances: rubber, gums, cellulose

Biomacromolecules

  • micromolecules: below 1000 Da (acid-soluble pool: 18 to about 800 Da)
  • macromolecules: typically about 10 000 Da and above in NCERT
  • acid-insoluble fraction: proteins, nucleic acids, polysaccharides, lipids
  • NCERT average cell water: 70–90 per cent by mass
  • NCERT average cell proteins: 10–15 per cent by mass

Proteins

  • protein: heteropolymer built mainly from 20 standard amino acids
  • homopolymer: one type of monomer repeated n times
  • essential amino acids: from the diet
  • collagen: most abundant protein in animals
  • RuBisCO: most abundant protein in the biosphere

Polysaccharides

  • cellulose, starch, glycogen: polymers of glucose
  • inulin: polymer of fructose
  • starch + iodine: blue
  • NCERT drawing: reducing-end position right; non-reducing branch ends left
  • chitin: arthropod exoskeletons

Nucleic acids

  • nucleotide: base + sugar + phosphate
  • purines: adenine, guanine
  • pyrimidines: cytosine, thymine, uracil
  • DNA: 2′-deoxyribose; RNA: ribose

Structure of proteins

  • primary: the sequence of amino acids
  • secondary: helix and other folded forms
  • tertiary: three-dimensional folding of the whole chain
  • quaternary: arrangement of subunits
  • predominant adult haemoglobin HbA: 2 α + 2 β subunits

Enzymes

  • rate = δP/δt
  • E + S ⇌ ES → EP → E + P
  • rough temperature rule: rate doubles/halves per 10°C over a limited range
  • carbonic anhydrase: about 10 million times faster
  • NCERT six classes: oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases
  • co-factors: prosthetic groups, co-enzymes, metal ions

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