18.04 Four Kingdoms of the Domain Eukarya

Overview

• Eukarya is one of the three domains, consisting of all organisms with eukaryotic cells.
• Divided into four main kingdoms based on cell structure, mode of nutrition, and reproduction:
  • Protoctista
  • Fungi
  • Plantae
  • Animalia

1. Kingdom Protoctista

• Characteristics:
  • Diverse group including unicellular, colonial, and simple multicellular organisms.
  • Includes algae, protozoa, and slime molds.
  • Habitat: Aquatic or moist environments.
• Cell Structure:
  • Eukaryotic, may have cell walls (composition varies) or no cell wall.
  • Some have chloroplasts for photosynthesis.
• Nutrition:
  • Autotrophic (e.g., algae) or heterotrophic (e.g., protozoa).
  • Some are mixotrophic (both autotrophic and heterotrophic).
• Reproduction:
  • Asexual (binary fission) or sexual (via gametes).

2. Kingdom Fungi

• Characteristics:
  • Includes molds, yeasts, and mushrooms.
• Cell Structure:
  • Eukaryotic, with a cell wall made of chitin (not cellulose).
  • No chloroplasts or photosynthetic pigments.
• Nutrition:
  • Heterotrophic, absorbing nutrients from decaying organic matter (saprotrophic) or living hosts (parasitic).
• Structure:
  • Most fungi are composed of thread-like structures called hyphae, which form a network called a mycelium.
• Reproduction:
  • Asexual (spores) and sexual reproduction.
• Ecological Role:
  • Decomposers in ecosystems, recycling nutrients.

3. Kingdom Plantae

• Characteristics:
  • Includes mosses, ferns, conifers, and flowering plants.
• Cell Structure:
  • Eukaryotic, with cell walls made of cellulose.
  • Contain chloroplasts with chlorophyll for photosynthesis.
• Nutrition:
  • Autotrophic: Perform photosynthesis using sunlight, CO₂, and water.
• Reproduction:
  • Asexual (spores, vegetative propagation) and sexual (via gametes, seeds).
• Structure:
  • Multicellular organisms with specialized tissues and organs.
  • Exhibit alternation of generations (sporophyte and gametophyte stages).
• Ecological Role:
  • Primary producers, forming the base of most food chains.

4. Kingdom Animalia

• Characteristics:
  • Includes all animals, from sponges to mammals.
• Cell Structure:
  • Eukaryotic, lack cell walls.
  • Specialized cells form tissues, organs, and systems.
• Nutrition:
  • Heterotrophic, ingesting and digesting food internally.
• Reproduction:
  • Mostly sexual reproduction with some asexual forms (e.g., budding in hydra).
• Movement:
  • Most animals have a nervous system for coordination and can move actively.
• Ecological Role:
  • Consumers in ecosystems, with roles ranging from herbivores to apex predators.

Summary Table of the Four Kingdoms