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

Alright class, let's focus on Chapter 7, 'Diversity in Living Organisms'. This is a crucial chapter, not just for your Class 9 understanding but also as a foundation for biology in competitive exams. Understanding how life is classified helps us make sense of the incredible variety around us.

Chapter 7: Diversity in Living Organisms - Detailed Notes for Exam Preparation

1. Basis of Classification:

• Why Classify? To study the vast number of organisms systematically, understand evolutionary relationships, and identify organisms easily.
• Characteristics Used: Organisms are grouped based on similarities and differences in their characteristics. These can range from simple (cell structure) to complex (body design, organ systems).
• Hierarchy of Classification: A system of arranging organisms into groups and sub-groups based on increasing similarity. Developed by Carolus Linnaeus.
  • Kingdom: Broadest category.
  • Phylum (for animals) / Division (for plants)
  • Class
  • Order
  • Family
  • Genus: Group of closely related species.
  • Species: Basic unit; group of organisms that can interbreed to produce fertile offspring.
  • (Mnemonic: Keep Pots Clean Or Family Gets Sick)

2. The Five Kingdom Classification (Proposed by R.H. Whittaker, 1969):

• Basis: Cell structure (prokaryotic/eukaryotic), Cell wall presence/composition, Mode of nutrition (autotrophic/heterotrophic), Body organization (unicellular/multicellular), Phylogenetic relationships.

• The Five Kingdoms:

  • Kingdom Monera:
    • Characteristics: Prokaryotic (no defined nucleus or organelles), Unicellular, Cell wall present (peptidoglycan, except Mycoplasma) or absent, Diverse modes of nutrition (autotrophic - chemosynthetic/photosynthetic; heterotrophic - saprophytic/parasitic).
    • Examples: Bacteria, Cyanobacteria (Blue-Green Algae), Mycoplasma (smallest living cells, lack cell wall).
  • Kingdom Protista:
    • Characteristics: Eukaryotic, Mostly Unicellular (some colonial/filamentous), Some have cell walls, Diverse nutrition (autotrophic - algae; heterotrophic - protozoans), Often possess cilia, flagella, or pseudopodia for locomotion. Acts as a link between Monera and multicellular eukaryotes.
    • Examples: Amoeba, Paramecium, Euglena (mixotrophic), Diatoms, Protozoans.
  • Kingdom Fungi:
    • Characteristics: Eukaryotic, Mostly Multicellular (exception: Yeast is unicellular), Heterotrophic (saprophytic - feed on dead organic matter; parasitic - feed on living hosts), Cell wall made of Chitin, Body consists of thread-like structures called hyphae (network = mycelium). Some form symbiotic associations (Lichens = Fungi + Algae; Mycorrhiza = Fungi + Roots of higher plants).
    • Examples: Yeast, Molds (Penicillium, Aspergillus), Mushrooms (Agaricus).
  • Kingdom Plantae:
    • Characteristics: Eukaryotic, Multicellular, Autotrophic (photosynthesis due to chlorophyll), Cell wall made of Cellulose, Primarily non-motile.
  • Kingdom Animalia:
    • Characteristics: Eukaryotic, Multicellular, Heterotrophic (holozoic, saprophytic, parasitic), Lack cell walls, Mostly motile, Exhibit complex tissue/organ/organ system organization.

3. Detailed Classification within Kingdom Plantae:

• Basis: Body differentiation (differentiated/undifferentiated), Presence of vascular tissues (xylem, phloem), Ability to bear seeds, Seeds enclosed in fruit or naked.

• Groups:

  • (Cryptogamae - Plants with hidden reproductive organs, reproduce by spores)
    • Division Thallophyta (Algae):
      • Undifferentiated plant body (thallus - no true roots, stem, leaves).
      • Primarily aquatic.
      • No vascular tissues.
      • Examples: Spirogyra, Ulothrix, Cladophora, Chara.
    • Division Bryophyta:
      • Called "Amphibians of the Plant Kingdom" (need water for fertilization).
      • Differentiated into stem-like and leaf-like structures, simple root-like structures (rhizoids).
      • No specialized vascular tissues.
      • Found in damp, shady places.
      • Examples: Mosses (Funaria), Liverworts (Marchantia, Riccia).
    • Division Pteridophyta:
      • First terrestrial plants with vascular tissues (xylem and phloem).
      • Differentiated into true roots, stem, and leaves.
      • Reproduce by spores (produced in sporangia, often on the underside of leaves).
      • Found in cool, damp, shady places.
      • Examples: Ferns (Dryopteris), Horsetails (Equisetum), Marsilea.
  • (Phanerogamae - Plants with well-developed reproductive organs, produce seeds)
    • Gymnosperms:
      • Bear naked seeds (not enclosed within a fruit).
      • Usually evergreen, perennial, and woody.
      • Vascular tissues present.
      • Examples: Pines (Pinus), Deodar (Cedrus), Cycads (Cycas).
    • Angiosperms (Flowering Plants):
      • Bear seeds enclosed within a fruit (develops from the ovary).
      • Flowers are the reproductive structures.
      • Highly diverse group, wide range of habitats.
      • Vascular tissues well-developed.
      • Sub-divided based on cotyledons:
        • Monocotyledons (Monocots): Seeds with one cotyledon, fibrous root system, parallel venation in leaves, floral parts usually in multiples of three. Examples: Maize, Wheat, Rice, Grass, Onion, Bamboo.
        • Dicotyledons (Dicots): Seeds with two cotyledons, tap root system, reticulate (net-like) venation in leaves, floral parts usually in multiples of four or five. Examples: Pea, Gram, Bean, Mustard, Mango, Rose, Sunflower.

4. Detailed Classification within Kingdom Animalia:

• Basis: Level of organization (cellular, tissue, organ, organ system), Body symmetry (asymmetrical, radial, bilateral), Germ layers (diploblastic - 2 layers; triploblastic - 3 layers), Nature of coelom (body cavity), Presence/absence of notochord.

• Major Phyla (Non-Chordates):

  • Phylum Porifera (Sponges):
    • Cellular level of organization, Asymmetrical, Diploblastic (loosely).
    • Pore-bearing body (ostia), central cavity (spongocoel), exit pore (osculum).
    • Canal system for water transport (food gathering, respiration, waste removal).
    • Sessile (non-motile), mostly marine.
    • Skeleton of spicules or spongin fibres.
    • Examples: Sycon, Spongilla (freshwater), Euplectella (Venus flower basket).
  • Phylum Coelenterata (Cnidaria):
    • Tissue level of organization, Radial symmetry, Diploblastic.
    • Presence of stinging cells (cnidoblasts or nematocysts) for anchorage, defense, capture of prey.
    • Central gastro-vascular cavity (coelenteron) with a single opening (mouth/anus).
    • Exist in two forms: Polyp (sessile, cylindrical - Hydra) and Medusa (free-swimming, umbrella-shaped - Jellyfish).
    • Examples: Hydra, Jellyfish (Aurelia), Sea Anemone (Adamsia), Corals.
  • Phylum Platyhelminthes (Flatworms):
    • Organ level of organization, Bilateral symmetry, Triploblastic, Acoelomate (no true body cavity).
    • Dorso-ventrally flattened body.
    • Mostly parasitic (some free-living).
    • Examples: Planaria (free-living, high regeneration), Liver Fluke (Fasciola), Tapeworm (Taenia).
  • Phylum Nematoda (Aschelminthes/Roundworms):
    • Organ system level of organization, Bilateral symmetry, Triploblastic, Pseudocoelomate (false coelom).
    • Cylindrical body, tapering at ends.
    • Complete digestive tract.
    • Many are parasitic, causing diseases.
    • Examples: Ascaris (intestinal roundworm), Wuchereria (filarial worm - causes elephantiasis), Pinworm.
  • Phylum Annelida (Segmented Worms):
    • Organ system level, Bilateral symmetry, Triploblastic, True Coelomate.
    • Body segmented externally and internally (metameric segmentation).
    • Well-developed circulatory (closed type) and nervous systems.
    • Locomotion by setae or parapodia.
    • Examples: Earthworm (Pheretima), Leech (Hirudinaria), Nereis (aquatic).
  • Phylum Arthropoda (Jointed-legged Animals):
    • Largest phylum in the animal kingdom.
    • Organ system level, Bilateral symmetry, Triploblastic, Coelomate.
    • Segmented body (head, thorax, abdomen).
    • Jointed appendages (legs, antennae).
    • Exoskeleton made of Chitin.
    • Open circulatory system.
    • Respiration by gills, book gills, book lungs, or tracheal system.
    • Examples: Insects (Cockroach, Butterfly, Housefly, Mosquito), Arachnids (Spider, Scorpion), Crustaceans (Prawn, Crab), Millipedes, Centipedes.
  • Phylum Mollusca (Soft-bodied Animals):
    • Second largest phylum.
    • Organ system level, Bilateral symmetry (some asymmetrical due to torsion), Triploblastic, Coelomate (reduced coelom).
    • Body unsegmented, usually divided into head, visceral hump, and muscular foot.
    • Often covered by a calcareous shell.
    • Mantle cavity present.
    • Examples: Snail (Pila), Mussel (Unio), Octopus, Squid, Cuttlefish, Oyster.
  • Phylum Echinodermata (Spiny-skinned Animals):
    • Exclusively marine.
    • Organ system level, Radial symmetry (adults), Bilateral symmetry (larvae), Triploblastic, Coelomate.
    • Endoskeleton of calcareous ossicles (spiny skin).
    • Presence of Water Vascular System (tube feet) for locomotion, feeding, respiration.
    • Examples: Starfish (Asterias), Sea Urchin (Echinus), Sea Cucumber (Holothuria), Brittle Star (Ophiura).

• Phylum Chordata:

  • Key Features (present at some stage of life):

    • Presence of a Notochord (flexible rod-like structure).
    • Dorsal hollow nerve cord.
    • Paired pharyngeal gill slits.
    • Post-anal tail.

  • Bilateral symmetry, Triploblastic, Coelomate, Organ system level.

  • Subphyla: Protochordata (Urochordata, Cephalochordata) and Vertebrata.

    • Protochordata: Notochord present but no true vertebral column. Marine. Examples: Balanoglossus, Herdmania, Amphioxus.
    • Vertebrata: Notochord replaced by a cartilaginous or bony vertebral column (backbone) in adults. Well-developed brain protected by cranium (skull).

  • Classes within Vertebrata:

    • Class Pisces (Fish):
      • Aquatic, streamlined body, scales, fins for locomotion, gills for respiration.
      • Cold-blooded (poikilothermic).
      • Two-chambered heart (1 auricle, 1 ventricle).
      • Lay eggs (oviparous).
      • Cartilaginous (Sharks) and Bony (Rohu, Tuna) fish.
    • Class Amphibia:
      • Live on land and in water ("dual life").
      • Smooth, moist skin (respiration), lungs (adults), gills (larvae).
      • Cold-blooded.
      • Three-chambered heart (2 auricles, 1 ventricle).
      • Lay eggs in water.
      • Examples: Frogs, Toads, Salamanders, Newts.
    • Class Reptilia:
      • Mostly terrestrial, body covered with dry scales.
      • Breathe through lungs.
      • Cold-blooded.
      • Mostly three-chambered heart (exception: Crocodiles have a four-chambered heart).
      • Lay eggs with tough shells on land (amniotic egg).
      • Examples: Snakes, Lizards, Turtles, Tortoises, Crocodiles, Alligators.
    • Class Aves (Birds):
      • Body covered with feathers, forelimbs modified into wings for flight (most).
      • Beak present, no teeth.
      • Breathe through lungs (air sacs supplement respiration).
      • Warm-blooded (homeothermic).
      • Four-chambered heart.
      • Bones are hollow (pneumatic) to reduce weight.
      • Lay eggs with hard shells.
      • Examples: Sparrow, Crow, Pigeon, Eagle, Ostrich (flightless), Penguin (flightless).
    • Class Mammalia:
      • Presence of mammary glands (produce milk).
      • Body covered with hair/fur.
      • External ears (pinnae) usually present.
      • Breathe through lungs, diaphragm present.
      • Warm-blooded.
      • Four-chambered heart.
      • Mostly viviparous (give birth to live young) - exceptions: Platypus, Echidna are oviparous (egg-laying).
      • Examples: Humans, Whales, Bats, Kangaroo, Rat, Cow, Tiger.

5. Binomial Nomenclature:

• System of naming organisms using two parts: Genus name and species name.
• Developed by Carolus Linnaeus.
• Rules:
  • Genus name starts with a capital letter.
  • Species name starts with a small letter.
  • When printed, names are in italics.
  • When handwritten, names are underlined separately (e.g., Homo sapiens).
• Example: Homo sapiens (Human), Mangifera indica (Mango), Panthera tigris (Tiger).

Multiple Choice Questions (MCQs):

1. Which of the following is the correct hierarchical order of classification?
   (a) Kingdom, Phylum, Class, Family, Order, Genus, Species
   (b) Kingdom, Phylum, Class, Order, Family, Genus, Species
   (c) Kingdom, Class, Phylum, Order, Family, Species, Genus
   (d) Phylum, Kingdom, Class, Order, Family, Genus, Species

2. Organisms belonging to Kingdom Monera are characterized by:
   (a) Eukaryotic cells and multicellular body
   (b) Prokaryotic cells and presence of chitin cell wall
   (c) Prokaryotic cells and absence of defined nucleus
   (d) Eukaryotic cells and autotrophic nutrition

3. Which group of plants is known as the 'amphibians of the plant kingdom'?
   (a) Thallophyta
   (b) Pteridophyta
   (c) Bryophyta
   (d) Gymnosperms

4. Which phylum is characterized by the presence of jointed appendages and a chitinous exoskeleton?
   (a) Annelida
   (b) Mollusca
   (c) Arthropoda
   (d) Echinodermata

5. Which class of vertebrates is characterized by feathers, pneumatic bones, and a four-chambered heart?
   (a) Reptilia
   (b) Aves
   (c) Mammalia
   (d) Amphibia

6. Gymnosperms are plants that:
   (a) Produce flowers and fruits
   (b) Lack vascular tissues
   (c) Have seeds enclosed within fruits
   (d) Have naked seeds not enclosed within fruits

7. Which of the following organisms is an example of Phylum Porifera?
   (a) Hydra
   (b) Starfish
   (c) Spongilla
   (d) Earthworm

8. Binomial nomenclature was introduced by:
   (a) R.H. Whittaker
   (b) Charles Darwin
   (c) Gregor Mendel
   (d) Carolus Linnaeus

9. Which of the following animal groups is cold-blooded (poikilothermic)?
   (a) Aves and Mammalia
   (b) Reptilia and Aves
   (c) Pisces, Amphibia, and Reptilia
   (d) Only Mammalia

10. The basic unit of classification is:
    (a) Genus
    (b) Family
    (c) Species
    (d) Kingdom

Answer Key for MCQs:

1. (b)
2. (c)
3. (c)
4. (c)
5. (b)
6. (d)
7. (c)
8. (d)
9. (c)
10. (c)

Study these notes thoroughly. Pay attention to the key characteristics and examples for each group, as these are frequently tested areas. Good luck with your preparation!