NCERT Class 11 Biotechnology Biotechnology: Chapter 7 — DNA as the Genetic Material
This chapter, 'DNA as the Genetic Material,' from NCERT Class 11 Biotechnology, delves into the fundamental concept of genetic inheritance. It explains that traits are passed from parents to offspring via genes, which reside on chromosomes composed of nucleic acids and proteins. The chapter highlights the historical challenge of identifying the gene's nature and introduces DNA as the primary determinant of an organism's traits, with exceptions in certain viruses. It traces the discovery of DNA by Johann Friedrich Miescher and discusses the early candidates for genetic material: nucleic acids and proteins. The text then details Frederick Griffith's groundbreaking 1928 experiment with Streptococcus pneumoniae, introducing the concepts of virulent (S strain) and non-virulent (R strain) bacteria and demonstrating the 'transforming principle' that DNA carries genetic information, crucial for CBSE learning.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Biotechnology |
| Book | Biotechnology |
| Chapter | Chapter 7 — DNA as the Genetic Material |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 3 minutes |
| Word count | 439 |
Learning outcomes
- Understand that genes carry traits from parents to offspring.
- Identify DNA as the primary genetic material in most organisms.
- Learn about the historical discovery of DNA and its role.
- Explain Griffith's transforming principle experiment.
- Differentiate between virulent (S) and non-virulent (R) bacterial strains.
Vocabulary
| Word | Meaning |
|---|---|
| Genes | Units of heredity that determine traits. |
| Chromosomes | Structures in the nucleus carrying genetic information. |
| Nucleic acids | Molecules like DNA and RNA that carry genetic information. |
| Nuclein | Acidic substance isolated from cell nuclei containing DNA and protein. |
| Virulent | Disease-causing. |
| Non-virulent | Harmless. |
| Polysaccharide capsule | Outer protective layer of some bacteria. |
| Transforming principle | The concept that genetic material can be transferred between bacteria. |
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Practice questions
- Who first isolated an acidic substance from cell nuclei and named it nuclein? Answer: Johann Friedrich Miescher.
- What bacterium did Frederick Griffith use in his experiments? Answer: Streptococcus pneumoniae (Diplococcus pneumoniae).
- What is the difference between the S strain and R strain of Streptococcus pneumoniae? Answer: The S strain has a polysaccharide capsule and is virulent, while the R strain lacks the capsule and is non-virulent.
- What observation did Griffith make that led to the concept of the transforming principle? Answer: He observed that heat-killed S strain bacteria, when mixed with live R strain bacteria, could transform the R strain into virulent S strain bacteria, causing mice to die.
Frequently asked questions
What is the primary role of DNA in organisms?
DNA serves as the genetic material, carrying the instructions for the development, functioning, growth, and reproduction of all known organisms.
Who is credited with the discovery of DNA?
Johann Friedrich Miescher is credited with the first isolation of DNA, which he named 'nuclein'.
What was Frederick Griffith's key experiment about?
Griffith's experiment demonstrated the 'transforming principle,' showing that genetic material could be transferred from dead virulent bacteria to live non-virulent bacteria, making them virulent.
What are the two strains of Streptococcus pneumoniae mentioned in the chapter?
The two strains are the virulent S (smooth) strain, which has a polysaccharide capsule, and the non-virulent R (rough) strain, which lacks the capsule.
Why were nucleic acids and proteins considered candidates for genetic material?
They were considered because they are the main chemical components found in chromosomes and nuclei, where genetic information is located.
Related resources
Important topics
Topics covered
NCERT Class 11 Biotechnology — Biotechnology — Chapter 7 — DNA as the Genetic Material. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.