Five Kingdom Classification

The five kingdom classification is a system of classifying living organisms into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. This classification was proposed by R.H. Whittaker in 1969 and is based on the following criteria:

• Complexity of cell structure: Prokaryotic or Eukaryotic.
• Complexity of body organization: Unicellular or Multicellular.
• Mode of nutrition: Autotrophic or Heterotrophic.
• Phylogenetic relationships: Evolutionary relationships between organisms.

1. Kingdom Monera

This kingdom includes unicellular prokaryotic organisms. They are the simplest and most ancient group of organisms.

Main Characteristics:

• Prokaryotic Cells: They lack a true nucleus and other membrane-bound organelles like mitochondria, chloroplasts, and endoplasmic reticulum. The genetic material is a single, circular DNA molecule, located in a region called the nucleoid.
• Cell Wall: Most monerans have a rigid cell wall made of peptidoglycan (murein), which provides structural support and protection.
• Nutrition: They exhibit diverse modes of nutrition:
  • Autotrophic: They can produce their own food.
    • Photosynthetic: They use light energy to synthesize food (e.g., Cyanobacteria).
    • Chemosynthetic: They obtain energy from the oxidation of inorganic chemical compounds (e.g., Nitrifying bacteria).
  • Heterotrophic: They obtain food from external sources.
    • Saprophytic: They feed on dead and decaying organic matter (e.g., Decomposing bacteria).
    • Parasitic: They live in or on other organisms (hosts) and obtain nourishment from them (e.g., Vibrio cholerae).
• Reproduction: They primarily reproduce asexually through binary fission.

Examples:

• Bacteria: Microscopic, single-celled organisms found everywhere. They can be classified based on their shape:
  • Cocci: Spherical (e.g., Streptococcus).
  • Bacilli: Rod-shaped (e.g., Escherichia coli).
  • Spirilla: Spiral-shaped (e.g., Spirillum volutans).
• Cyanobacteria (Blue-Green Algae): Photosynthetic bacteria that contain chlorophyll. They are known for their ability to fix atmospheric nitrogen (e.g., Nostoc, Anabaena).

2. Kingdom Protista

This kingdom includes unicellular eukaryotic organisms. They are considered to be the ancestors of multicellular eukaryotes.

Main Characteristics:

• Eukaryotic Cells: They have a true nucleus and other membrane-bound organelles.
• Locomotion: Many protists are motile and move using:
  • Pseudopodia: Temporary extensions of the cytoplasm (e.g., Amoeba).
  • Cilia: Short, hair-like structures (e.g., Paramecium).
  • Flagella: Long, whip-like structures (e.g., Euglena).
• Nutrition: They show various modes of nutrition:
  • Autotrophic (Algae-like): They are photosynthetic (e.g., Diatoms, Chlamydomonas).
  • Heterotrophic (Protozoans): They ingest food (e.g., Amoeba, Paramecium).
  • Mixotrophic: They can be both autotrophic and heterotrophic (e.g., Euglena).
• Reproduction: They reproduce both asexually (binary fission, multiple fission) and sexually (conjugation).

Examples:

• Amoeba: A simple protozoan that moves and feeds using pseudopodia.
• Paramecium: A ciliated protozoan with a definite shape and a specialized feeding groove.

3. Kingdom Fungi

This kingdom includes eukaryotic, heterotrophic organisms. They were previously classified as plants, but they lack chlorophyll and have a different cell wall composition.

Main Characteristics:

• Eukaryotic Cells: They have a true nucleus and membrane-bound organelles.
• Body Structure: Most fungi are multicellular and their body is composed of a network of thread-like structures called hyphae. This network is known as the mycelium. Some fungi, like yeast, are unicellular.
• Cell Wall: Their cell walls are made of a complex polysaccharide called chitin.
• Nutrition: They are heterotrophic and obtain nutrients by absorption:
  • Saprophytic: They obtain nutrients from dead organic matter (e.g., Mushrooms, Molds).
  • Parasitic: They live on or in other living organisms and cause diseases (e.g., Puccinia - rust fungus).
  • Symbiotic: They live in a mutually beneficial relationship with other organisms. For example, lichens are a symbiotic association between a fungus and an alga.
• Reproduction: They reproduce both asexually (spore formation, budding) and sexually.

Examples:

• Mushrooms: The fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source.
• Yeasts: Unicellular fungi that are used in the baking and brewing industries.

4. Kingdom Plantae

This kingdom includes multicellular, eukaryotic, and autotrophic organisms. They are the primary producers in most ecosystems.

Main Characteristics:

• Eukaryotic Cells: They have a true nucleus and membrane-bound organelles, including chloroplasts for photosynthesis.
• Cell Wall: Their cell walls are made of cellulose.
• Nutrition: They are autotrophic and prepare their own food through photosynthesis.
• Body Organization: They have a well-differentiated body with specialized tissues and organs.

Subdivisions of Kingdom Plantae

(i) Thallophyta (Algae)

• Plant Body: They have a simple, undifferentiated plant body called a thallus. They lack true roots, stems, and leaves.
• Habitat: They are predominantly aquatic, found in both freshwater and marine environments.
• Examples: Spirogyra (Green algae), Laminaria (Brown algae), Polysiphonia (Red algae).

(ii) Bryophyta (Mosses)

• Plant Body: They have a more differentiated body than algae, with simple stem-like and leaf-like structures, but they lack true roots. They are attached to the substratum by root-like structures called rhizoids.
• Habitat: They are often called the "amphibians of the plant kingdom" because they live in moist, shady places and require water for sexual reproduction.
• Vascular System: They lack a specialized vascular system (xylem and phloem) for the transport of water and food.
• Examples: Mosses (Funaria), Liverworts (Marchantia).

(iii) Pteridophyta (Ferns)

• Plant Body: They are the first terrestrial plants to possess a well-differentiated body with true roots, stems, and leaves.
• Vascular System: They have a well-developed vascular system (xylem and phloem).
• Reproduction: They reproduce by forming spores in specialized structures called sporangia.
• Examples: Ferns (Dryopteris), Horsetails (Equisetum).

(iv) Spermatophyta (Seed Plants)

• These are the most advanced group of plants. Their defining characteristic is the presence of seeds for reproduction.
• They are further divided into two groups:
  • Gymnosperms: They bear "naked" seeds, meaning the seeds are not enclosed within a fruit. (e.g., Pinus, Cycas).
  • Angiosperms (Flowering Plants): They bear seeds that are enclosed within a fruit. They are the largest and most diverse group of plants. (e.g., Mango, Rose, Wheat).

5. Kingdom Animalia

This kingdom includes multicellular, eukaryotic, and heterotrophic organisms. They are characterized by their ability to move and respond to stimuli.

Main Characteristics:

• Eukaryotic Cells: They have a true nucleus and membrane-bound organelles. They lack cell walls and chloroplasts.
• Nutrition: They are heterotrophic and ingest their food.
• Body Organization: They have a well-differentiated body with specialized tissues, organs, and organ systems.
• Motility: Most animals are motile, meaning they can move from one place to another.

Subdivisions of Kingdom Animalia

(A) Non-Chordates

These are animals without a notochord (a flexible rod-like structure that supports the body).

• Phylum Porifera (Sponges):

  • Pore-bearing animals with a cellular level of organization.
  • They have a unique canal system for water circulation.
  • Example: Sycon (Sponge).

• Phylum Coelenterata (Cnidaria):

  • They have a hollow body cavity (coelenteron) and tentacles with stinging cells (cnidoblasts).
  • Examples: Hydra, Jellyfish.

• Phylum Platyhelminthes (Flatworms):

  • They have a dorso-ventrally flattened body.
  • Many are parasitic.
  • Examples: Tapeworm, Liver fluke.

• Phylum Nematoda (Roundworms):

  • They have a cylindrical body, tapering at both ends.
  • Many are parasitic and cause diseases.
  • Example: Ascaris (Roundworm).

• Phylum Annelida (Segmented Worms):

  • They have a segmented body and a true coelom (body cavity).
  • Examples: Earthworm, Leech.

• Phylum Arthropoda (Jointed-legged Animals):

  • This is the largest phylum in the animal kingdom.
  • They have a chitinous exoskeleton and jointed appendages.
  • Examples: Insects (Cockroach), Spiders, Prawns.

• Phylum Mollusca (Soft-bodied Animals):

  • They have a soft body, which is usually covered by a hard calcareous shell.
  • They have a muscular foot for locomotion.
  • Examples: Snail, Octopus.

• Phylum Echinodermata (Spiny-skinned Animals):

  • They are exclusively marine animals with a spiny skin.
  • Adults show radial symmetry.
  • They have a unique water vascular system for locomotion and feeding.
  • Examples: Starfish, Sea urchin.

(B) Chordates

These are animals that possess a notochord at some stage of their life. They also have a dorsal hollow nerve cord and pharyngeal gill slits.

• Class Pisces (Fish):

  • Aquatic animals with a streamlined body.
  • They breathe through gills and have fins for locomotion.
  • They are cold-blooded (poikilothermic).
  • Examples: Rohu, Shark.

• Class Amphibia (Amphibians):

  • They can live both on land and in water.
  • They have moist, glandular skin for respiration.
  • They lay their eggs in water.
  • They are cold-blooded.
  • Examples: Frogs, Toads, Salamanders.

• Class Reptilia (Reptiles):

  • They are primarily terrestrial animals with dry, scaly skin.
  • They breathe through lungs.
  • They lay eggs with a tough, protective shell on land.
  • They are cold-blooded.
  • Examples: Lizards, Snakes, Turtles, Crocodiles.

• Class Aves (Birds):

  • Their body is covered with feathers, and their forelimbs are modified into wings for flight.
  • They have a light, streamlined body with hollow bones.
  • They are warm-blooded (homeothermic).
  • They lay hard-shelled eggs.
  • Examples: Crow, Pigeon, Ostrich.

• Class Mammalia (Mammals):

  • They are the most advanced group of animals.
  • Their body is covered with hair.
  • They have mammary glands to produce milk for nourishing their young.
  • They are warm-blooded.
  • Most of them give birth to live young (viviparous).
  • Examples: Humans, Whales, Bats, Kangaroo.