NCERT Class 11 Biology Biology: Chapter 9 — Biomolecules
NCERT Class 11 Biology Chapter 9, Biomolecules, explores the chemical composition of living organisms. It details how elemental analysis reveals that living tissues and non-living matter share common elements, but their relative abundance differs, with carbon and hydrogen being more prevalent in organisms. The chapter introduces the process of chemical analysis using trichloroacetic acid to separate living tissue into an acid-soluble pool (containing primary and secondary metabolites) and an acid-insoluble fraction. It also explains how burning tissue yields ash, indicating inorganic constituents. Biomolecules are classified into organic compounds like amino acids, nucleotides, and fatty acids, and inorganic compounds. Amino acids, the building blocks of proteins, are discussed as substituted methanes with a common structure and a variable R group, leading to twenty different types found in proteins. This chapter provides a foundational understanding of the molecular basis of life.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Biology |
| Book | Biology |
| Chapter | Chapter 9 — Biomolecules |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 4 minutes |
| Word count | 800 |
Learning outcomes
- Understand the elemental and compound composition of living organisms.
- Differentiate between primary and secondary metabolites.
- Learn the process of chemical analysis to identify biomolecules.
- Identify the basic structure and types of amino acids.
- Recognize the presence of inorganic constituents in living tissues.
Vocabulary
| Word | Meaning |
|---|---|
| Biosphere | The part of the earth where life exists. |
| Metabolites | Substances formed in or broken down by living organisms. |
| Acid-soluble pool | The fraction of a homogenized tissue extract that dissolves in trichloroacetic acid. |
| Acid-insoluble fraction | The precipitate remaining after homogenizing and filtering a tissue extract in trichloroacetic acid. |
| Biomolecules | Organic compounds found in living tissues. |
| Ash | The inorganic residue remaining after burning organic matter. |
| Amino acids | Organic compounds containing an amino group and an acidic group, building blocks of proteins. |
| α-carbon | The central carbon atom in an amino acid to which the amino group, carboxyl group, hydrogen, and R group are attached. |
| R group | The variable side chain in an amino acid that determines its specific properties. |
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Practice questions
- What are the two fractions obtained when a living tissue is ground in trichloroacetic acid? Answer: The acid-soluble pool (filtrate) and the acid-insoluble fraction (retentate).
- What does the ash of a burnt living tissue represent? Answer: The ash represents the inorganic elements and compounds present in the living tissue.
- What is the basic structure of an α-amino acid? Answer: An α-amino acid has a carboxyl group, an amino group, a hydrogen atom, and a variable R group attached to the α-carbon.
- How do the relative abundances of elements in living organisms compare to earth's crust? Answer: The relative abundance of carbon and hydrogen is higher in living organisms compared to the earth's crust.
Frequently asked questions
What is the main difference between the elemental composition of living organisms and non-living matter like earth's crust?
While both share common elements, living organisms have a significantly higher relative abundance of carbon and hydrogen compared to the earth's crust.
How are biomolecules identified and analyzed in a living tissue?
By grinding the tissue in trichloroacetic acid, separating it into an acid-soluble pool and an acid-insoluble fraction, and then applying various analytical and separation techniques.
What are the two main categories of compounds found in living organisms?
Living organisms contain both organic compounds (biomolecules) and inorganic elements and compounds.
What is an amino acid?
An amino acid is an organic compound containing an amino group and an acidic group, serving as the building blocks of proteins.
How many types of amino acids are commonly found in proteins?
There are twenty different types of amino acids that commonly occur in proteins.
What is the significance of the R group in an amino acid?
The R group is the variable side chain of an amino acid, and its nature determines the specific properties of each amino acid.
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NCERT Class 11 Biology — Biology — Chapter 9 — Biomolecules. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.