Animal Kingdom Revision Summary (NCERT Class 11)
1. Chapter at a Glance
- Fundamental features used for classification are levels of organisation, symmetry, diploblastic/triploblastic organisation, coelom, segmentation and notochord.
- Levels of organisation range from cellular (Porifera) to tissue (Coelenterata, Ctenophora), organ (Platyhelminthes) and organ-system (higher phyla).
- Symmetry types: asymmetrical (sponges), radial (Coelenterata, Ctenophora, Echinodermata adults) and bilateral (most others).
- Coelom types: coelomates (true coelom lined by mesoderm), pseudocoelomates (Aschelminthes) and acoelomates (Platyhelminthes).
- Chordates possess notochord, dorsal hollow nerve cord, paired pharyngeal gill slits and post-anal tail; non-chordates lack notochord.
- Vertebrata divided into Agnatha (Cyclostomata) and Gnathostomata (Chondrichthyes, Osteichthyes, Tetrapoda).
- Key distinctions include open vs closed circulatory system, incomplete vs complete digestive system, and metameric segmentation (Annelida, Arthropoda).
2. Definitions and Laws
- Levels of Organisation: Cellular level (loose cell aggregates, e.g., sponges); tissue level (cells arranged into tissues, e.g., coelenterates); organ level (tissues grouped into organs); organ-system level (organs associated into functional systems).
- Symmetry: Asymmetrical (any plane through centre does not divide into equal halves); radial symmetry (“any plane passing through the central axis of the body divides the organism into two identical halves”); bilateral symmetry (body divisible into identical left and right halves in only one plane).
- Diploblastic and Triploblastic Organisation: Diploblastic animals have cells arranged in two embryonic layers (ectoderm and endoderm) with mesoglea in between; triploblastic animals have a third germinal layer, mesoderm, between ectoderm and endoderm.
- Coelom: “The body cavity, which is lined by mesoderm is called coelom. Animals possessing coelom are called coelomates”; pseudocoelom (mesoderm present as scattered pouches); acoelomate (body cavity absent).
- Segmentation: Body “externally and internally divided into segments with a serial repetition of at least some organs”; phenomenon called metamerism.
- Notochord: “Notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals. Animals with notochord are called chordates and those animals which do not form this structure are called non-chordates.”
- Chordates vs non-chordates (Table 4.1): Notochord present/absent; CNS dorsal hollow single/ventral solid double; pharyngeal gill slits present/absent; heart ventral/dorsal; post-anal tail present/absent.
3. Important Diagrams and Activities
- Figure 4.1: Radial symmetry and bilateral symmetry – demonstrates body plan division by planes.
- Figure 4.2: Diploblastic (ectoderm, mesoglea, endoderm) and triploblastic (ectoderm, mesoderm, endoderm) organisation – shows germinal layers.
- Figure 4.3: Diagrammatic sectional view of coelomate, pseudocoelomate and acoelomate – illustrates position of mesoderm and body cavity.
- Figure 4.4: Broad classification of Kingdom Animalia – shows branching based on fundamental features.
- Figure 4.6 & 4.7: Polyp and medusa body forms; cnidoblast – shows alternation of generations (metagenesis) and stinging cells.
- Figure 4.16: Chordata characteristics (notochord, dorsal hollow nerve cord, post-anal tail, gill slits) – fundamental chordate features.
- Figure 4.18–4.24: Representative animals of Cyclostomata to Mammalia – required for identifying class-specific traits.
4. Common Misconceptions and Exam Pitfalls
- Echinodermata adults show radial symmetry but larvae are bilaterally symmetrical (do not state only radial).
- All chordates are not vertebrates; vertebrates replace notochord with vertebral column in adults.
- Open circulatory system (blood pumped out, tissues bathed directly) vs closed (blood through vessels) must be matched exactly to phyla.
- Incomplete digestive system (single opening) occurs only in Platyhelminthes and Coelenterata; higher phyla have complete system.
- Metamerism/segmentation first appears in Annelida, not Arthropoda or others.
- Hemichordata has stomochord (not true notochord) and is now a separate phylum, not under Chordata.
5. Formula Sheet
No mathematical formulas or equations in the chapter.