Which of the following is correctly related to chordates?

Appeared in: DSSSB 6 September 2024

Explanation

Chordates are characterized by having a heart located on the ventral (front or belly) side of the body.
This is a key distinguishing feature when comparing the body plans of chordates with non-chordates, which typically have a dorsal heart if one is present.
Among the given choices, 'Ventral heart' is a complete and accurate characteristic of all chordates.

Option B: All chordates possess pharyngeal gill slits at some stage of their life cycle. In terrestrial vertebrates like humans, these are present only in the embryonic stage and later develop into other structures.
Option C: While technically true that chordates have a dorsal nerve system, this statement is incomplete. The full, defining feature is a dorsal, hollow, and single nerve cord. Because this description is less precise than 'Ventral heart', it is not the best answer.
Option D: This is incorrect. The presence of a notochord, a flexible rod-like structure for support, is the primary defining characteristic of the phylum Chordata. It must be present at some stage of development.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Fundamental characteristics of Phylum Chordata as background academic context rather than a clinical decision trigger.
Understanding the basic chordate body plan is fundamental to human anatomy, as humans belong to this phylum.
Knowledge of the embryological development of these chordate structures is crucial for understanding congenital anomalies. For example, defects in the closure of the dorsal neural tube can lead to conditions like spina bifida.
What if? If an animal was discovered with a dorsal heart and a ventral nerve cord, it would be classified as a non-chordate (likely an invertebrate like an arthropod or annelid), as this body plan is the inverse of the chordate plan.

How to Approach the Question

First, identify the core subject: the defining features of the phylum Chordata.
Recall the fundamental characteristics of chordates: 1) Notochord, 2) Dorsal hollow nerve cord, 3) Pharyngeal gill slits, 4) Post-anal tail, and 5) Ventral heart.
Systematically evaluate each option against these characteristics.
Eliminate options that are definitively false: 'Gill slits absent' and 'Notochord absent' are incorrect as these features are present in chordates.
Compare the remaining options: 'Ventral heart' and 'Dorsal nerve system'. Both describe chordate features.
Select the 'best' answer. 'Ventral heart' is a complete and precise statement. 'Dorsal nerve system' is an incomplete description (missing 'hollow' and 'single'), making it a weaker choice. Therefore, 'Ventral heart' is the most accurate answer.

Concept Tested & Keywords

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