Ch 4 classifies animals based on body plan features — levels of organisation, symmetry, germ layers, coelom, segmentation, and notochord — covering all major phyla from Porifera to Chordata.
Levels of organisation: cellular → tissue → organ → organ system. Symmetry: asymmetrical (sponges), radial (cnidaria), bilateral (most). Germ layers: diploblastic (2 — cnidaria), triploblastic (3 — all others). Coelom: acoelomate (no cavity — flatworms), pseudocoelomate (false — roundworms), coelomate (true — annelids+). Segmentation: present in annelids, arthropods, chordates.
Porifera: pore-bearing, sessile, spicules. Cnidaria: cnidocytes, radial symmetry. Platyhelminthes: flat, acoelomate (tapeworm, liver fluke). Nematoda: pseudocoelomate (Ascaris). Annelida: segmented, true coelom (earthworm, leech). Arthropoda: jointed legs, exoskeleton, largest phylum. Mollusca: soft body, shell (snail, octopus). Echinodermata: spiny skin, water vascular system (starfish). Chordata: notochord, dorsal nerve cord, gill slits.
Download: https://ncert.nic.in/textbook/pdf/kebo104.pdf | Complete book: https://ncert.nic.in/textbook/pdf/kebo1ps.zip
A coelom is a fluid-filled body cavity between the body wall and gut, lined by mesoderm. It provides space for organ development and growth, acts as a hydrostatic skeleton in soft-bodied organisms, allows organs to move independently of the body wall, and facilitates circulation of nutrients and wastes.
Book a Trial + Diagnostic session. Get a personalized Learning Path with clear milestones, tutor match, and a plan recommendation — all within 24 hours.
Book Trial + Diagnostic →