Class 9th || Science || Notes || Chapter 7: Diversity in Living Organisms

Introduction

The world of living organisms is incredibly diverse. With millions of species of plants, animals, and microorganisms, it becomes necessary to classify them in a systematic way. This classification helps in understanding their similarities, differences, evolutionary relationships, and interactions with the environment.

Importance of Classification

• Facilitates Study: Helps in systematically studying a vast number of organisms.
• Understanding Evolutionary Relationships: Classification helps in tracing evolutionary links between different species.
• Convenience: It makes the study of organisms simpler and more organized.

Basis of Classification

Organisms are classified based on similarities and differences. The major characteristics considered for classification are:

1. Cell Structure:

   • Prokaryotic cells: Cells without a well-defined nucleus (e.g., bacteria).
   • Eukaryotic cells: Cells with a well-defined nucleus (e.g., plants and animals).

2. Mode of Nutrition:

   • Autotrophic: Organisms that can prepare their food (e.g., plants).
   • Heterotrophic: Organisms that depend on others for food (e.g., animals, fungi).

3. Level of Organization:

   • Unicellular: Organisms consisting of a single cell (e.g., Amoeba).
   • Multicellular: Organisms consisting of multiple cells (e.g., humans, trees).

4. Body Design and Symmetry:

   • Radial Symmetry: The body can be divided into equal halves through any plane (e.g., jellyfish).
   • Bilateral Symmetry: The body can only be divided into two equal halves through one plane (e.g., humans).

Hierarchy of Classification (Taxonomic Categories)

In biological classification, organisms are categorized into a hierarchy, starting from the broadest to the most specific groups:

• Kingdom: Broadest category (e.g., Kingdom Plantae, Kingdom Animalia).
• Phylum: Groups of related classes (e.g., Phylum Chordata).
• Class: Groups of related orders (e.g., Class Mammalia).
• Order: Groups of related families (e.g., Order Carnivora).
• Family: Groups of related genera (e.g., Family Felidae).
• Genus: Groups of related species (e.g., Genus Panthera).
• Species: Most specific category, individuals capable of interbreeding (e.g., Species Panthera leo).

The Five Kingdom Classification

This system was proposed by Robert Whittaker in 1969 and is widely accepted today. It divides all living organisms into five major kingdoms:

1. Kingdom Monera:

   • Cell Type: Prokaryotic (no nucleus).
   • Cell Number: Mostly unicellular.
   • Mode of Nutrition: Autotrophic or heterotrophic.
   • Examples: Bacteria, Cyanobacteria (blue-green algae).

2. Kingdom Protista:

   • Cell Type: Eukaryotic.
   • Cell Number: Mostly unicellular.
   • Mode of Nutrition: Autotrophic or heterotrophic.
   • Examples: Amoeba, Paramecium, Algae.

3. Kingdom Fungi:

   • Cell Type: Eukaryotic.
   • Cell Number: Mostly multicellular (except yeast, which is unicellular).
   • Mode of Nutrition: Heterotrophic (saprophytic or parasitic).
   • Examples: Yeast, Mushroom, Molds.

4. Kingdom Plantae:

   • Cell Type: Eukaryotic.
   • Cell Number: Multicellular.
   • Mode of Nutrition: Autotrophic (photosynthesis).
   • Examples: Trees, Flowers, Ferns, Mosses.

5. Kingdom Animalia:

   • Cell Type: Eukaryotic.
   • Cell Number: Multicellular.
   • Mode of Nutrition: Heterotrophic.
   • Examples: Insects, Mammals, Birds, Reptiles, Fish.

Classification of Plants

Plants are classified into several divisions based on the presence of organs like roots, stems, leaves, and the presence or absence of seeds and flowers.

1. Thallophyta (Algae):

   • Characteristics: Simple body design, no true roots, stems, or leaves.
   • Examples: Spirogyra, Chara.

2. Bryophyta:

   • Characteristics: Possess leaf-like structures, but no true roots or stems.
   • Examples: Mosses, Liverworts.

3. Pteridophyta:

   • Characteristics: Have true roots, stems, and leaves, but reproduce through spores, not seeds.
   • Examples: Ferns.

4. Gymnosperms:

   • Characteristics: Bear naked seeds (not enclosed in fruits).
   • Examples: Pines, Deodar.

5. Angiosperms:

   • Characteristics: Have seeds enclosed in fruits; also divided into monocots (one cotyledon) and dicots (two cotyledons).
   • Examples: Mango, Rose, Wheat.

Classification of Animals

Animals are broadly classified into two groups:

• Invertebrates: Animals without a backbone (e.g., sponges, insects).
• Vertebrates: Animals with a backbone (e.g., fish, birds, mammals).

1. Porifera:

   • Characteristics: Simplest animals, with pores all over their body, no tissues or organs.
   • Examples: Sponges.

2. Coelenterata:

   • Characteristics: Hollow body cavity, radial symmetry.
   • Examples: Jellyfish, Hydra.

3. Platyhelminthes:

   • Characteristics: Flat, ribbon-like bodies.
   • Examples: Tapeworms, Liver flukes.

4. Nematoda:

   • Characteristics: Round, unsegmented bodies.
   • Examples: Ascaris, Pinworms.

5. Annelida:

   • Characteristics: Segmented bodies, bilateral symmetry.
   • Examples: Earthworms, Leeches.

6. Arthropoda:

   • Characteristics: Exoskeleton, segmented body, jointed limbs.
   • Examples: Insects, Spiders, Crabs.

7. Mollusca:

   • Characteristics: Soft body, often with a hard shell.
   • Examples: Snails, Octopus.

8. Echinodermata:

   • Characteristics: Radial symmetry, spiny skin.
   • Examples: Starfish, Sea urchin.

9. Chordata:

   • Characteristics: Presence of a notochord, dorsal nerve cord, and post-anal tail at some stage of life.
   • Subphyla:
     • Pisces (Fish): Gills for respiration, scales, fins.
     • Amphibia: Live in water and land, moist skin (e.g., frogs, salamanders).
     • Reptilia: Scales, cold-blooded (e.g., snakes, lizards).
     • Aves (Birds): Feathers, beaks, wings (e.g., eagles, sparrows).
     • Mammalia: Warm-blooded, have hair, produce milk (e.g., humans, lions).