Problem 152 - Objective Biology for NEET

Question

Which is not a distinctive character of non-chordata? (a) Notochordal is absent (b) Ventral and double nerve cord (c) Heart is ventral (d) Post-anal tail is absent

Step-by-Step Solution

Answer

The non-distinctive character of non-chordata is option (b): Ventral and double nerve cord.

Step 1: Understand the Characteristics of Non-Chordata

Non-chordates are a group of animals that do not possess the notochord at any stage of their life. Some of the characteristics are: Notochord is absent, the nerve cord if present is ventral and single, heart is dorsal if present, and post-anal tail is usually absent.

Step 2: Analyze Each Option Based on These Characteristics

A. True for non-chordata as notochord is absent. B. False for non-chordata as they have a single ventral nerve cord not double. C. True for non-chordata, as the heart is usually dorsal in non-chordata, if it is present. D. True for non-chordata, as generally, post-anal tail is absent.

Step 3: Identify the Non-characteristic

From the above analysis, we can tell that option b is not a characteristic of non-chordata as the nervous system in them is usually single not double.

Key Concepts

Notochord

The notochord is a flexible rod-shaped structure that forms the main support of the body in all embryonic and some adult chordate animals. It is an essential component of the defining characteristics of chordates, a group which includes animals like fish, amphibians, reptiles, birds, and mammals, including humans.
In contrast, non-chordates do not possess a notochord at any stage in their life cycle. This absence is a key feature used to differentiate between chordates and non-chordates. However, non-chordates comprise a vast array of living beings, including organisms like arthropods, mollusks, and annelids.
While the presence or absence of a notochord can seem straightforward, its evolutionary role in providing axial support before the development of the vertebral column in vertebrates highlights its importance in the animal kingdom.

Nerve Cord

The nerve cord is another significant distinction between chordates and non-chordates. In chordates, the nerve cord is typically dorsal and tubular, often developing into the central nervous system, which consists of the brain and spinal cord.
For non-chordates, the nerve cord is generally situated on the ventral side and is usually solid rather than hollow or tube-like. This fundamental difference reflects the separate evolutionary paths taken by these two groups.
While chordates possess a more complex nervous system facilitating advanced functions, non-chordates have a simpler nerve structure which often limits their neurological capabilities. Understanding the location and structural differences of the nerve cord helps clarify the evolutionary advancements in the animal kingdom.

Dorsal Heart

In the animal kingdom, the position of the heart can be a critical differentiator. For chordates, the heart is ventral, meaning it is located on the front side of the body. This ventral positioning supports efficient circulation of blood in larger, more anatomically complex organisms.
Non-chordates, on the other hand, generally exhibit a dorsal heart, when a heart is present. This means it is located on the back side of the body. In some non-chordates, due to their simpler circulatory needs, the heart itself may be completely absent.
The dorsal positioning of the heart in non-chordates represents their less complex circulatory demands compared to chordates. This variance in heart placement is an intriguing facet in the study of animal anatomy and evolution.

Post-anal Tail

A post-anal tail is a tail that extends beyond the anus and is considered one of the key characteristics of chordates. This feature is present in varying degrees in many chordate species throughout their entire life or during some stage of their development.
In non-chordates, the absence of a post-anal tail is common. This distinction helps in identifying the variety of life forms between chordates and non-chordates.
The post-anal tail serves various functions in locomotion, balance, or communication, depending on the species. Its absence in non-chordates suggests different adaptive strategies for survival.
Exploring the development and presence of a post-anal tail in animals helps illustrate the diverse ways in which life on Earth has evolved to adapt to environmental challenges.