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BASIS OF CLASSIFICATION, LEVELS OF ORGANISATION, , * Cellular level of organisation, * Tissue level of organisation, * Organ level of organisation, * Organ system level of organisation, 1.Cellular level of organisation, * The cells are arranged as loose cell aggregates. Eg- sponges, 2 Tissue level of organisation, * Here the cells performing the same function, are grouped into tissues., ¢ Eg:-coelenterates, 3.Organ level of organisation, * Here tissues are grouped together to form organs, for doing a particular function., ¢ Eg:-Platyheiminthes and other higher phyla (Round worms), 4.Organ system level of organisation, , * Different organs have associated to form organ systems, for doing a specific, function., , * Eg-Arthropods, Molluscs, Echinoderms and Chordates, Annelids,

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Body Plan, , Animals have three basic body plans. They are, , a., , Cell aggregate plan, , Itis the simplest type of body plan seen in sponges belonging to porifera.In, this, body is only a loose aggregation of cells without tissues and organs., Eventhough tissues and organs are absent,each function is carried out, by single cells., , The blind sac body plan, , It is a slightly advanced type of body plan shown by coelenterates,, ctenophores and flat worms. Here the animals have a digestive cavity like, sac with only one opening to the outside. The single opening serves as, mouth (for ingestion) and anus (egestion)., , The tube-within-a-tube body plan, , It is the highly advanced type of body plan shown by complex animal, groups. Here the body consists of two tubes, the outer body wall and the, inner alimentary canal. It looks like a tube of small diameter inserted into, the tube of large diameter. The alimentary canal has separate openings, for ingestion (mouth) and egestion (anus)., , , , Cell aggregate body Blind sac body plan Tube within a tube, plar-(in a sponge) (in a hydra) plan (in a fish), , Body Plan