Class 9 Science – Chapter 7: Diversity in Living Organisms (Detailed Notes)

Class 9 Science – Chapter 7: Diversity in Living Organisms (Detailed Notes)

1. Introduction

• There are millions of living organisms on Earth with great diversity in size, form, habitat, and mode of nutrition.
• Biological classification helps in understanding this diversity by grouping organisms based on similarities.
• Evolution plays a key role in diversity; new species arise through gradual changes over generations.

2. Basis of Classification

• Cell structure – Prokaryotic or Eukaryotic
• Body organization – Unicellular or Multicellular
• Mode of nutrition – Autotrophic or Heterotrophic
• Presence or absence of a cell wall
• Level of body organization – Tissue, organ, or organ system

3. Hierarchy of Classification

• Kingdom → Phylum → Class → Order → Family → Genus → Species
• As we move from Kingdom to Species, similarities increase and diversity decreases.

4. Five Kingdom Classification (R.H. Whittaker – 1969)

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

4.1 Kingdom Monera

• Unicellular, prokaryotic organisms (e.g., bacteria)
• No well-defined nucleus or organelles
• Can be autotrophic or heterotrophic

4.2 Kingdom Protista

• Unicellular, eukaryotic organisms
• Have well-defined nucleus and organelles
• Examples: Amoeba, Paramecium, Euglena

4.3 Kingdom Fungi

• Multicellular, eukaryotic, heterotrophic (mostly saprophytic)
• Cell walls made of chitin
• Reproduce by spores
• Examples: Rhizopus, Penicillium, Mushrooms

4.4 Kingdom Plantae

• Multicellular, eukaryotic, autotrophic (photosynthetic)
• Have chlorophyll, cell wall made of cellulose
• Show tissue and organ-level organization

4.5 Kingdom Animalia

• Multicellular, eukaryotic, heterotrophic
• No cell wall, well-developed organ systems
• Complex behavior and movement

5. Classification of Plants

5.1 Thallophyta

• Simplest plants, body is thallus-like (no roots, stems, or leaves)
• Examples: Algae – Spirogyra, Ulothrix

5.2 Bryophyta

• Amphibians of the plant kingdom
• Have root-like, stem-like, and leaf-like structures
• No vascular tissues
• Examples: Moss, Marchantia

5.3 Pteridophyta

• Have true roots, stems, and leaves with vascular tissues
• Do not bear seeds
• Examples: Fern, Marsilea

5.4 Gymnosperms

• Bear naked seeds (not enclosed in fruits)
• Have roots, stems, leaves, vascular tissues
• Examples: Pine, Cycas

5.5 Angiosperms

• Flowering plants that bear seeds inside fruits
• Dicots: Two cotyledons (e.g., mango, rose)
• Monocots: One cotyledon (e.g., wheat, rice)

6. Classification of Animals

6.1 Porifera (Sponges)

• Pores all over body, no true tissues or organs
• Non-motile, aquatic
• Example: Sycon, Spongilla

6.2 Coelenterata (Cnidaria)

• Body cavity, radial symmetry
• Have tentacles and nematocysts (stinging cells)
• Example: Hydra, Jellyfish

6.3 Platyhelminthes (Flatworms)

• Dorsoventrally flat, bilaterally symmetrical
• Mostly parasites
• Example: Planaria, Tapeworm

6.4 Nematoda (Roundworms)

• Cylindrical body, bilaterally symmetrical
• Parasites – cause diseases in plants and animals
• Example: Ascaris

6.5 Annelida (Segmented worms)

• Body divided into segments
• Closed circulatory system
• Example: Earthworm, Leech

6.6 Arthropoda

• Largest group, jointed legs, exoskeleton
• Open circulatory system
• Examples: Insects, Spiders, Crabs

6.7 Mollusca

• Soft body, usually with a hard shell
• Unsegmented, bilateral symmetry
• Example: Snail, Octopus

6.8 Echinodermata

• Spiny skin, radial symmetry, marine
• Have water vascular system
• Example: Starfish, Sea urchin

6.9 Chordata

• Have notochord, nerve cord, and paired gill slits at some stage
• Sub-divided into:
  • Pisces (Fish)
  • Amphibia (Frog)
  • Reptilia (Lizard)
  • Aves (Birds)
  • Mammalia (Humans)