Chapter-1: The Living World - Complete Guide for Biology Class 11

Your ultimate guide to understanding the first chapter of Biology Class 11, featuring key points, concepts, taxonomical aids, and more!

Introduction to The Living World

The living world comprises a vast diversity of plants, animals, and microorganisms. Understanding their characteristics, classification, and nomenclature is essential for organizing and studying this diversity systematically.

Points to Remember

Characteristics of Living Organisms

1. Growth
2. Reproduction
3. Metabolism
4. Cellular Organisation
5. Consciousness (ability to sense the environment)
6. Self-replication and Self-regulation

Note:

• Growth and Reproduction are NOT defining properties as non-living objects can also grow, and some organisms do not reproduce (e.g., mules, sterile bees).
• Metabolism, Cellular Organisation, and Consciousness are the true defining properties of life.

Biodiversity and Need for Classification

Biodiversity refers to the variety of plants and animals on Earth. Classification helps:

• Organize organisms into categories.
• Facilitate naming, studying, and understanding the vast diversity.

Nomenclature Rules

To give scientific names to plants and animals, Binomial Nomenclature is used.

1. Latinised names are used.
2. First word: Genus (starts with a capital letter).
3. Second word: Species (starts with a small letter).
4. Names are italicized in print or underlined separately when handwritten.

Example: Mangifera indica Linn.
Here, “Linn.” indicates that the species was first described by Carolus Linnaeus.

ICBN and ICZN

• ICBN: International Code of Botanical Nomenclature (for plants)
• ICZN: International Code of Zoological Nomenclature (for animals)

Taxonomy and Systematics

Taxonomy

Taxonomy is the study of classification principles and procedures.

Systematics

Systematics classifies organisms based on their diversities and relationships.

• Proposed by Carolus Linnaeus in Systema Naturae.

Taxonomic Hierarchy

The classification system arranges living organisms in a hierarchy of categories:

Species → Genus → Family → Order → Class → Phylum/Division → Kingdom

Concept of Species

• Organisms that can interbreed and produce fertile offspring belong to the same species.
• Proposed by Mayr as the biological concept of species.

Three Domains of Life

Proposed by Carl Woese in 1990, the three domains are:

1. Archaea → Archaebacteria
2. Eubacteria → Monera
3. Eukaryota → Protista, Mycota (Fungi), Plantae, Animalia

Taxonomical Aids

1. Herbarium

• A storehouse of dried, pressed, and preserved plant specimens mounted on sheets.

2. Botanical Garden

• A collection of living plants for reference.
• Examples:
  • Kew Botanical Garden (England)
  • National Botanical Research Institute (Lucknow, India)

3. Zoological Parks

• Wild animals are kept in a protected environment.

4. Keys

• Used for identifying plants and animals based on similarities and differences.

5. Flora

• An index of plant species found in a specific area.

6. Manuals

• Provide information to identify the names of species in an area.

7. Monograph

• Detailed information about a specific taxon.

Important Questions & Answers

Very Short Answer Questions (1 Mark)

Q1. Define species.
Ans: Members that can interbreed to produce fertile offspring.

Q2. What is systematics?
Ans: Systematics studies evolutionary relationships and the systematic arrangement of organisms.

Q3. Name two famous botanical gardens.
Ans:

1. Kew Botanical Garden (England)
2. National Botanical Research Institute (Lucknow)

Short Answer Questions-II (2 Marks)

Q4. What is the basis of modern taxonomical studies?
Ans: Modern taxonomy is based on:

• External and internal structure.
• Cell structure.
• Development processes.
• Ecological information.

Q5. Why are growth and reproduction NOT defining properties of all living organisms?
Ans:

1. Non-living things can increase in mass by accumulation of material.
2. Some organisms (e.g., mules, sterile bees) do not reproduce.

Q6. How is a taxon defined?
Ans: Each category in the taxonomical hierarchy is called a taxon.

Short Answer Questions-I (3 Marks)

Q7. Difference between Botanical Garden and Herbarium.

Q8. How are Keys useful for classification?
Ans: Keys are analytical tools used to identify organisms based on similarities and dissimilarities.

Q9. Define the following terms:

• Genus: Group of related species.
• Family: Group of related genera.
• Order: Group of related families.

Long Answer Questions (5 Marks)

Q10. What are the universal rules of nomenclature? What does 'Linn.' refer to in Mangifera indica Linn.?
Ans: Refer to the Nomenclature Rules above. ‘Linn.’ refers to Carolus Linnaeus, who first described the species.

Q11. Illustrate taxonomical hierarchy with examples.
Ans: Example:

1. Plant Species: Mango

   • Species: indica
   • Genus: Mangifera
   • Family: Anacardiaceae
   • Order: Sapindales
   • Class: Dicotyledonae
   • Division: Angiosperms

2. Animal Species: Tiger

   • Species: tigris
   • Genus: Panthera
   • Family: Felidae
   • Order: Carnivora
   • Class: Mammalia
   • Phylum: Chordata