Question

Which of the following are correct?
(i) Sponges : Cellular level of organisation
(ii) Cnidaria : Tissue level of organisation
(iii) Platyhelminthes : Organ level of organisation
(iv) Annelids, Arthropods, Molluscs, Echinoderms and Chordates : Organ system level of organisation.

• A. (i), (ii), (iii) and (iv)
• B. (i) and (ii) only
• C. (ii) and (iv) only
• D. (ii) and (iii) only

Answer 1

Answer: (A)

Animals show four different grades of organization:
(i) Protoplasmic grade found in protozoans.
(ii) Cellular grade is the characteristic of sponges and mesozoans because in a sponge, cells exhibit division of labour for performing specialized functions.
(iii) Tissue grade is of two types : Cell-tissue grade is seen in coelenterates as there are cells not only specialised for different functions 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.
(iv) 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.

Hence the correct option is D.