Class 9 Science Notes | Diversity in Living Organisms Notes

Diversity in Living Organisms

Introduction: The chapter "Diversity in Living Organisms" from the Class 9 Science curriculum delves into the variety of life forms on Earth. This chapter provides an understanding of the classification of living organisms and the basis for such classifications, aiming to highlight the evolutionary relationships and the biodiversity of our planet.

Biodiversity: Biodiversity refers to the variety of life forms in a particular habitat or ecosystem. It encompasses the different plants, animals, microorganisms, and the ecosystems they form. Biodiversity is crucial for maintaining ecological balance and providing resources for survival.

Classification: Classification is the systematic arrangement of living organisms into groups based on their similarities and differences. It helps in understanding the relationships among various organisms and makes the study of a wide variety of life forms manageable. The classification system has evolved over time, from Aristotle's simple classification to the more complex and detailed systems we use today.

Five Kingdom Classification: R.H. Whittaker proposed the five-kingdom classification in 1969, which includes:

1. Monera
2. Protista
3. Fungi
4. Plantae
5. Animalia

1. Monera:

• Characteristics:

  • Unicellular organisms.
  • Prokaryotic cell structure (no true nucleus or membrane-bound organelles).
  • Reproduction mainly by binary fission.
  • Includes bacteria and blue-green algae (cyanobacteria).

• Examples:

  • Escherichia coli (E. coli)
  • Streptococcus
  • Cyanobacteria (blue-green algae)

2. Protista:

• Characteristics:

  • Mostly unicellular, some are multicellular.
  • Eukaryotic cell structure (true nucleus and membrane-bound organelles).
  • Can be autotrophic or heterotrophic.
  • Reproduce asexually and sexually.

• Examples:

  • Amoeba
  • Paramecium
  • Algae (like Chlamydomonas)

3. Fungi:

• Characteristics:

  • Mostly multicellular (except yeast which is unicellular).
  • Eukaryotic cell structure.
  • Cell walls made of chitin.
  • Heterotrophic, absorbing nutrients from decomposing organic material.
  • Reproduce by spores.

• Examples:

  • Mushrooms
  • Yeast
  • Molds (like Rhizopus)

4. Plantae:

• Characteristics:

  • Multicellular organisms.
  • Eukaryotic cell structure.
  • Cell walls made of cellulose.
  • Autotrophic, performing photosynthesis using chlorophyll.
  • Includes a wide range of organisms from simple algae to complex flowering plants.

• Examples:

  • Mosses
  • Ferns
  • Flowering plants (like roses, oak trees)

5. Animalia:

• Characteristics:

  • Multicellular organisms.
  • Eukaryotic cell structure.
  • No cell walls.
  • Heterotrophic, consuming organic material for nutrition.
  • Highly diverse group ranging from simple sponges to complex mammals.

• Examples:

  • Sponges
  • Insects
  • Fish
  • Birds
  • Mammals

Basis of Classification: The classification of living organisms is based on several criteria:

• Cell Structure: Prokaryotic (without a nucleus) or eukaryotic (with a nucleus).
• Body Organization: Unicellular or multicellular.
• Mode of Nutrition: Autotrophic (producing own food) or heterotrophic (consuming other organisms).
• Reproduction: Asexual or sexual methods.
• Phylogenetic Relationships: Evolutionary history and common ancestry.

Hierarchy of Classification: The classification system is hierarchical, with each level called a taxon. The major levels are:

• Kingdom
• Phylum (for animals) / Division (for plants)
• Class
• Order
• Family
• Genus
• Species

Nomenclature: Scientific naming of organisms follows binomial nomenclature, introduced by Carl Linnaeus. Each organism has a two-part Latin name - the genus name (capitalized) and the species name (lowercase). For example, Homo sapiens (human beings).

Plant Kingdom Classification: The plant kingdom is divided into several groups based on complexity and features:

• Thallophyta: Simple, body not differentiated into root, stem, and leaves (e.g., algae).
• Bryophyta: Non-vascular plants with simple structures (e.g., mosses).
• Pteridophyta: Vascular plants with true roots, stems, and leaves but no seeds (e.g., ferns).
• Gymnosperms: Vascular plants with naked seeds (e.g., pine trees).
• Angiosperms: Vascular plants with seeds enclosed within fruits (flowering plants).

Animal Kingdom Classification: The animal kingdom is divided into various phyla based on body structure and organization:

• Porifera: Simplest animals with porous bodies (e.g., sponges).
• Coelenterata (Cnidaria): Radially symmetrical animals with a central cavity (e.g., jellyfish, corals).
• Platyhelminthes: Flatworms with bilateral symmetry (e.g., tapeworms).
• Nematoda: Roundworms with a cylindrical body (e.g., Ascaris).
• Annelida: Segmented worms with a true coelom (e.g., earthworms).
• Arthropoda: Animals with jointed legs and exoskeletons (e.g., insects, spiders, crustaceans).
• Mollusca: Soft-bodied animals, usually with a shell (e.g., snails, clams, octopuses).
• Echinodermata: Radially symmetrical marine animals with spiny skin (e.g., starfish).
• Chordata: Animals with a notochord, dorsal nerve cord, and pharyngeal slits at some stage in their life (e.g., fish, amphibians, reptiles, birds, mammals).

Vertebrates and Invertebrates:

• Invertebrates: Animals without a backbone (e.g., insects, mollusks, crustaceans).
• Vertebrates: Animals with a backbone, classified into five classes:
  • Pisces (Fish): Aquatic, gills for respiration (e.g., sharks, bony fish).
  • Amphibia: Live in water and on land, moist skin (e.g., frogs, salamanders).
  • Reptilia: Dry skin with scales, lay eggs on land (e.g., lizards, snakes).
  • Aves (Birds): Feathers, beaks, and lay eggs (e.g., sparrows, eagles).
  • Mammalia: Hair or fur, mammary glands, live births in most cases (e.g., humans, whales, bats).

Significance of Classification: Classification helps in:

• Understanding the diversity of life forms.
• Identifying and naming organisms.
• Understanding evolutionary relationships.
• Studying the distribution and habitat of organisms.
• Conservation of biodiversity by highlighting the importance of different species and ecosystems.

Conclusion: The chapter "Diversity in Living Organisms" offers a comprehensive insight into the classification and organization of life forms on Earth. It emphasizes the importance of understanding biodiversity and the evolutionary relationships that connect different species. This knowledge is fundamental to the fields of biology, ecology, and environmental science, fostering a deeper appreciation for the vast array of life that inhabits our planet.