Class 11 Biology Chapter 4: Kingdom Animalia – SSC Board

Class 11 Biology – Chapter 4: Kingdom Animalia (SSC Board)

The animal kingdom is vast and diverse, encompassing millions of species ranging from microscopic organisms to large mammals. Chapter 4 of the Class 11 SSC Board Biology textbook, “Kingdom Animalia,” explores this diversity by classifying animals based on their structure, complexity, and evolutionary features.

Learn about Kingdom Animalia from Class 11 SSC Board Biology Chapter 4. Covers animal classification, general features, phyla of invertebrates and vertebrates with examples and characteristics.

1. Introduction to Kingdom Animalia

• Kingdom Animalia includes multicellular, eukaryotic, heterotrophic organisms.
• Animals lack cell walls and depend on other organisms for food (heterotrophs).
• Most animals are motile (can move) and exhibit complex body organization.
• Reproduction is mainly sexual, and they develop from a blastula during embryonic development.

2. Basis of Animal Classification

Animals are classified based on:

• Level of organization (cellular, tissue, organ, organ system)
• Symmetry (asymmetrical, radial, bilateral)
• Germ layers (diploblastic, triploblastic)
• Body cavity (coelom): acoelomate, pseudocoelomate, coelomate
• Segmentation
• Notochord presence

3. Levels of Body Organization

1. Cellular Level – Cells loosely arranged (e.g., Porifera)
2. Tissue Level – Cells organized into tissues (e.g., Cnidaria)
3. Organ Level – Tissues form organs (e.g., Platyhelminthes)
4. Organ System Level – Organs form complex systems (e.g., Annelida, Chordata)

4. Symmetry in Animals

• Asymmetrical – No symmetry (e.g., Sponges)
• Radial Symmetry – Body parts arranged around a central axis (e.g., Cnidarians)
• Bilateral Symmetry – Divided into mirror halves (e.g., Humans, Worms)

5. Germ Layers

• Diploblastic – Two layers: ectoderm and endoderm (e.g., Cnidaria)
• Triploblastic – Three layers: ectoderm, mesoderm, endoderm (e.g., all higher animals)

6. Body Cavity (Coelom)

• Acoelomate – No body cavity (e.g., Flatworms)
• Pseudocoelomate – False cavity (e.g., Roundworms)
• Coelomate – True body cavity (e.g., Annelids, Chordates)

7. Classification of Animal Kingdom (Phyla)

Animals are broadly divided into:

• Invertebrates (no backbone)
• Vertebrates (with backbone, under Phylum Chordata)

8. Non-Chordates (Invertebrates)

a) Phylum Porifera (Sponges)

• Simplest animals; cellular level organization
• Asymmetrical, aquatic
• Example: Sycon, Spongilla

b) Phylum Coelenterata / Cnidaria

• Radial symmetry, tissue-level organization
• Stinging cells (cnidoblasts)
• Example: Hydra, Jellyfish, Sea anemone

c) Phylum Platyhelminthes (Flatworms)

• Bilateral symmetry, triploblastic
• Acoelomate, flat body
• Example: Planaria, Liver fluke, Tapeworm

d) Phylum Nematoda (Roundworms)

• Bilateral symmetry, pseudocoelomates
• Unsegmented, parasitic
• Example: Ascaris, Filaria worm

e) Phylum Annelida (Segmented Worms)

• Segmented, coelomate, organ system level
• Closed circulatory system
• Example: Earthworm, Leech

f) Phylum Arthropoda

• Largest phylum; jointed legs, exoskeleton
• Open circulatory system
• Example: Insects, Spiders, Crabs

g) Phylum Mollusca

• Soft-bodied, often with shells
• Unsegmented, coelomate
• Example: Snail, Octopus, Pila



h) Phylum Echinodermata

• Radial symmetry (adults), spiny skin
• Marine, water vascular system
• Example: Starfish, Sea urchin

9. Phylum Chordata (Vertebrates and Some Invertebrates)

Key features of chordates:

• Notochord (at least in embryonic stage)
• Dorsal nerve cord
• Pharyngeal slits
• Post-anal tail

Chordata is divided into:

• Urochordata and Cephalochordata (non-vertebrate chordates)
• Vertebrata (true backbone)

10. Classes of Vertebrates (Subphylum Vertebrata)

A. Class Pisces (Fishes)

• Aquatic, gills, fins
• Cold-blooded
• Example: Shark, Rohu

B. Class Amphibia

• Live on land and water
• Moist skin, no scales
• Cold-blooded
• Example: Frog, Toad

C. Class Reptilia

• Dry scaly skin
• Lay shelled eggs
• Cold-blooded
• Example: Lizard, Snake

D. Class Aves (Birds)

• Feathers, beaks, lay eggs
• Warm-blooded
• Example: Parrot, Sparrow

E. Class Mammalia

• Hair, mammary glands, give birth to young (mostly)
• Warm-blooded
• Example: Human, Cow, Tiger

Chapter 4 – Kingdom Animalia – helps students explore the rich diversity of animals. From the simplest sponges to complex mammals, the animal kingdom is classified based on structural complexity, body organization, and evolutionary traits. This classification system is not just for academic study, but it also helps in understanding evolutionary relationships, ecological roles, and the importance of animals in nature and human life.

Key Terms

• Symmetry: Radial, bilateral
• Coelom: Body cavity
• Invertebrates: Animals without backbone
• Chordates: Animals with notochord
• Vertebrates: Chordates with a backbone