NCERT Solutions for Class 11 Biology Chapter 4 Animal Kingdom
NCERT Solutions for Class 11 Biology Chapter 4 Animal Kingdom provides comprehensive explanations of animal classification criteria (symmetry, coelom, germ layers, segmentation, notochord) and detailed characteristics of non-chordate and chordate phyla.
Overview of Topics & Subtopics (Click to Jump)
1. Basis of Classification
Short Note:
• Levels of Organisation: Cellular (e.g., Porifera), Tissue level (Coelenterata), Organ level (Platyhelminthes), Organ-system level (Aschelminthes to Chordates).
• Symmetry: Asymmetrical (Sponges), Radial symmetry (Coelenterates, Ctenophores, Echinoderm adults), Bilateral symmetry (Annelids, Arthropods, Chordates).
• Germinal Layers: Diploblastic (Ectoderm + Endoderm e.g., Coelenterates) vs. Triploblastic (Ectoderm + Mesoderm + Endoderm e.g., Platyhelminthes to Chordates).
• Coelom (Body Cavity):
- Acoelomates: Cavity absent (Platyhelminthes).
- Pseudocoelomates: Mesoderm present as scattered pouches (Aschelminthes).
- Coelomates (Eucoelomates): True body cavity lined by mesoderm (Annelids to Chordates).
• Segmentation & Notochord: Metameric segmentation seen in Annelids and Arthropods. Notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in chordates.
2. Non-Chordate Phyla
Short Note:
• Porifera (Sponges): Cellular level, ostia (pores), osculum, choanocytes (collar cells) line spongocoel; internal skeleton of spicules/spongin fibers. E.g., Sycon, Spongilla.
• Coelenterata (Cnidaria): Cnidoblasts/cnidocytes containing nematocysts. Show alternation of generation (metagenesis) between Polyp (sessile) and Medusa (free-swimming). E.g., Hydra, Aurelia, Obelia, Physalia.
• Ctenophora (Comb Jellies): Exclusively marine, 8 rows of ciliated comb plates, show bioluminescence. E.g., Pleurobrachia, Ctenoplana.
• Platyhelminthes (Flatworms): Dorso-ventrally flattened, acoelomate, flame cells for osmoregulation/excretion. E.g., Taenia (tapeworm), Fasciola (liver fluke).
• Aschelminthes (Roundworms): Pseudocoelomates, complete digestive tract with muscular pharynx. E.g., Ascaris, Wuchereria (filarial worm).
• Annelida: True coelomates, metameric segmentation, nephridia for excretion. E.g., Nereis, Pheretima (earthworm), Hirudinaria (leech).
• Arthropoda: Largest phylum; chitinous exoskeleton, jointed appendages, open circulatory system, Malpighian tubules. E.g., Apis, Anopheles, Palaemon, Limulus.
• Mollusca: Second largest phylum; soft body covered by calcareous shell, mantle cavity with gills, radula (rasping organ). E.g., Pila, Pinctada, Octopus.
• Echinodermata: Spiny-skinned, radial symmetry in adults, water vascular system for locomotion/feeding. E.g., Asterias (starfish), Echinus.
• Hemichordata: Worm-like marine animals; body consists of Proboscis, Collar, and Trunk. E.g., Balanoglossus, Saccoglossus.
3. Phylum Chordata Overview
Short Note:
• Fundamental chordate characters: Presence of a Notochord, Dorsal hollow nerve cord, paired pharyngeal gill slits, and a post-anal tail.
• Subphylum Urochordata (Tunicata): Notochord present only in larval tail. E.g., Ascidia, Salpa.
• Subphylum Cephalochordata: Notochord extends from head to tail region and persists throughout life. E.g., Branchiostoma (Amphioxus).
• Subphylum Vertebrata: Notochord is replaced by a cartilaginous or bony vertebral column in adults.
4. Classes of Vertebrata
Short Note:
• Cyclostomata: Jawless vertebrates (Agnatha), suctorial circular mouth, ectoparasites on fishes. E.g., Petromyzon (Lamprey), Myxine (Hagfish).
• Chondrichthyes (Cartilaginous Fishes): Marine, stream-lined body, cartilaginous endoskeleton, placoid scales, ventral mouth, air bladder absent. E.g., Scoliodon (dogfish), Pristis (saw fish), Torpedo (electric ray).
• Osteichthyes (Bony Fishes): Marine and freshwater, bony endoskeleton, operculum covering gills, ctenoid/cycloid scales, air bladder present (regulates buoyancy). E.g., Exocoetus, Labeo, Betta.
• Amphibia: Can live in aquatic and terrestrial habitats, moist skin without scales, 3-chambered heart (2 auricles + 1 ventricle), poikilotherms. E.g., Rana (frog), Bufo (toad), Salamandra.
• Reptilia: Creeping/crawling mode of locomotion, dry and cornified skin with epidermal scales/scutes, 3-chambered heart (4-chambered in crocodiles). E.g., Chelone, Calotes, Naja, Crocodilus.
• Aves (Birds): Presence of feathers, forelimbs modified into wings, pneumatic (hollow) bones, 4-chambered heart, homoiothermous (warm-blooded). E.g., Corvus, Columba, Psittacula, Pavo.
• Mammalia: Presence of mammary glands, hair on skin, external ears (pinnae), 4-chambered heart, homoiothermous. E.g., Ornithorhynchus (oviparous platypus), Macropus (kangaroo), Panthera leo.
Intext & Conceptual Questions
| Feature | Chordates | Non-Chordates |
|---|---|---|
| Notochord | Present at some stage of life. | Absent. |
| Central Nervous System | Dorsal, hollow, and single. | Ventral, solid, and double. |
| Pharyngeal Gill Slits | Present. | Absent. |
| Heart Position | Ventral. | Dorsal (if present). |
| Post-anal Tail | Present. | Absent. |
Textbook Chapter End Exercise Questions
The body cavity (coelom)—the fluid-filled space between the body wall and the alimentary canal—is a vital diagnostic character in animal classification:
1. Acoelomates: Absence of body cavity (e.g., Platyhelminthes). The space is filled with parenchyma tissue, restricting organ independence.
2. Pseudocoelomates: Body cavity is not lined by mesoderm; mesoderm exists as scattered pouches inside the blastocoel (e.g., Aschelminthes).
3. Coelomates (Eucoelomates): Body cavity completely lined by mesoderm on both sides (e.g., Annelida to Chordata). This permits independent movement and development of complex internal visceral organs.
| Character | Chondrichthyes | Osteichthyes |
|---|---|---|
| Endoskeleton | Cartilaginous. | Bony. |
| Habitat | Exclusively marine. | Freshwater and marine. |
| Mouth Position | Ventral. | Terminal. |
| Operculum & Air Bladder | Operculum absent; air bladder absent (must swim constantly). | Operculum present over gills; air bladder present for buoyancy. |
| Scales | Placoid scales. | Cycloid or Ctenoid scales. |
Read More & Chapter Resources
These short notes are designed for quick revision. Read the main points once, then use the related material below to practise the same chapter. Revising a concept and checking it with questions can make your preparation more focused.