Organ Systems and Body Complexity — NEET Biology
📚 Practice ConceptEchinoderms and Chordates, organs have associated to form functional systems, each system concerned with a specific physiological function. This pattern is called organ system level of organisation. Organ systems in different groups of animals exhibit various patterns of complexities. For example, the digestive system in Platyhelminthes has only a single opening to the outside of the body that serves as both mouth and anus, and is hence called incomplete. A complete digestive system has two openings, mouth and anus. Similarly, the circulatory system may be of two types:
Arrange the following phyla in increasing order of complexity with respect to their level of organization and presence/type of coelom: I. Coelenterata II. Aschelminthes III. Annelida IV. Platyhelminthes V. Porifera
View solution & NCERT explanation
Correct answer: D — V → I → IV → II → III
The complexity of animal body plans generally increases from cellular level to organ-system level, from diploblastic to triploblastic organization, and from acoelomate to pseudocoelomate to coelomate. Let's analyze each phylum: * **V. Porifera:** Cellular level of organisation. (NCERT, page 37) * **I. Coelenterata:** Tissue level of organisation, diploblastic, and acoelomate. (NCERT, page 37, 38, 39) * **IV. Platyhelminthes:** Organ level of organisation, triploblastic, and acoelomate. (NCERT, page 37, 39, 42) * **II. Aschelminthes:** Organ-system level of organisation, triploblastic, and pseudocoelomate. (NCERT, page 43) * **III. Annelida:** Organ-system level of organisation, triploblastic, and coelomate. (NCERT, page 43) Arranging them in increasing order of complexity: 1. **Porifera (V)**: Simplest, with cellular level of organisation. 2. **Coelenterata (I)**: Next in complexity, with tissue level of organisation and diploblastic, but still acoelomate. 3. **Platyhelminthes (IV)**: More complex than coelenterates, with organ level of organisation and triploblastic, though still acoelomate. 4. **Aschelminthes (II)**: Exhibits organ-system level of organisation, triploblastic, and introduces a pseudocoelom, which is a step up from acoelomate. 5. **Annelida (III)**: Most complex among these, with organ-system level of organisation, triploblastic, and possessing a true coelom. Thus, the correct increasing order of complexity is V → I → IV → II → III.
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.