A) Sponges: Cellular level of organization
B) Cnidaria: Tissue level of organization
C) Platyhelminthes: Organ level of organization
D) Annelids, Arthropods, Molluscs, Echinoderms and Chordates: Organ system level of organization.
Correct Answer: A
Solution :
[a] Animals display four different grades of organization, [a] Protoplasmic grade found in protozoans, [b] Cellular grade is the characteristic of sponges and mesozoans in a sponge, cells exhibit division of labour for performing specializing functions, [c] Tissue grade is of two types: Cell-tissue grade is seen in coelenterates as there are cells not only specialized for different fimctions but also certain similar cells gather together to form tissue as well. Tissue- organ grade appears in flatworms (Platyhelminthes) with arrangement of tissues to form organs, [d] In organ system level of organisation, organs are joined in a system to perform basic functions. It is found in higher invertebrates and all vertebrates.
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