The Animal Kingdom chapter in Class 11 Biology lays the foundation for understanding how animals are grouped, identified, and studied scientifically. This PDF covers the complete NCERT-aligned explanation of animal classification, starting from the basic criteria used for grouping animals to a detailed discussion of non-chordates and chordates. It explains why animals differ in structure, organisation, and function, and how these differences help scientists classify them into well-defined groups.
I am writing about this PDF because the Animal Kingdom chapter is one of the most concept-heavy units in Class 11 Biology and is often confusing for students. A clear breakdown of what the chapter actually covers helps learners revise better, prepare for exams confidently, and understand how different animal groups are related to each other biologically. This article stays fully aligned with the uploaded PDF and explains its content in simple, student-friendly language.
Basis of Classification of Animals
The PDF begins by explaining that animals are classified using certain fundamental features. These features help in grouping animals based on similarities and differences rather than appearance alone.
Levels of Organisation
Animals show different levels of body organisation:
- Cellular level of organisation is seen in sponges, where cells are loosely arranged without forming tissues
- Tissue level of organisation occurs in coelenterates, where similar cells group to form tissues
- Organ level of organisation is observed in flatworms
- Organ-system level of organisation is found in higher animals like annelids, arthropods, molluscs, echinoderms, and chordates
The PDF clearly explains how complexity increases from simple cell aggregates to well-defined organ systems.
Symmetry
Animals are grouped based on body symmetry:
- Asymmetrical animals like sponges cannot be divided into equal halves
- Radial symmetry is seen in coelenterates, ctenophores, and echinoderms
- Bilateral symmetry is observed in annelids, arthropods, and chordates
Diploblastic and Triploblastic Organisation
The PDF explains embryonic layers in detail:
- Diploblastic animals have two germ layers – ectoderm and endoderm
- Triploblastic animals have three germ layers – ectoderm, mesoderm, and endoderm
This distinction is essential for understanding body cavity formation.
Coelom (Body Cavity)
Based on the presence or absence of coelom, animals are classified as:
- Acoelomates – no body cavity
- Pseudocoelomates – body cavity not fully lined by mesoderm
- Coelomates – true body cavity completely lined by mesoderm
This concept is explained with clear definitions and examples
Download this CLASS 11 – ANIMAL KINGDOM PDF File: Click Here
Classification of Non-Chordates
The PDF then moves into a detailed classification of non-chordate animals, explaining each phylum with key characteristics and examples.
Phylum Porifera
- Commonly known as sponges
- Cellular level of organisation
- Presence of canal system and spongocoel
- Digestion is intracellular
Phylum Coelenterata (Cnidaria)
- Aquatic animals with radial symmetry
- Tissue level of organisation
- Presence of cnidoblasts for defence
- Exhibit polyp and medusa forms
Phylum Ctenophora
- Marine animals known as comb jellies
- Eight rows of ciliated comb plates
- Show bioluminescence
Phylum Platyhelminthes
- Flatworms with bilateral symmetry
- Triploblastic and acoelomate
- Many are parasitic
Phylum Aschelminthes
- Roundworms
- Pseudocoelomate animals
- Complete digestive system
Phylum Annelida
- Segmented body showing metamerism
- True coelom and closed circulatory system
Phylum Arthropoda
- Largest phylum in Animal Kingdom
- Jointed appendages and chitinous exoskeleton
- Open circulatory system
Phylum Mollusca
- Soft-bodied animals with shell
- Presence of mantle and radula
Phylum Echinodermata
- Marine animals with water vascular system
- Adult radial symmetry and larval bilateral symmetry
Phylum Hemichordata
- Worm-like marine animals
- Body divided into proboscis, collar, and trunk
Phylum Chordata and Its Major Features
The PDF clearly explains that chordates are identified by the presence of:
- Notochord
- Dorsal hollow nerve cord
- Pharyngeal gill slits
- Post-anal tail
It also provides a comparison table between chordates and non-chordates, highlighting structural and functional differences.
Classification of Chordates
Chordates are divided into three subphyla:
Urochordata
- Notochord present only in larval stage
Cephalochordata
- Notochord present throughout life
Vertebrata
- Notochord replaced by vertebral column in adults
The PDF further classifies vertebrates into:
- Cyclostomata (jawless vertebrates)
- Pisces (Chondrichthyes and Osteichthyes)
- Amphibia
- Reptilia
- Aves
- Mammalia
Each class is explained with key identifying features, heart structure, body temperature regulation, reproduction type, and examples.
