Problem 160 - Objective Biology for NEET

Question

Select the incorrect statement from the following: (a) In vertebrates, the notochord is replaced by cartilaginous or bony vertebral column. (b) In cephalochordates, the notochord is extended from head to tail region and is persistent throughout life. (c) Protochordates are exclusively marine. (d) Notochord is present in tail of adult in urochordata.

Step-by-Step Solution

Answer

The incorrect statement is (d). Notochord is present in tail of adult in urochordata.

Step 1: Evaluate statement A

In vertebrates, the notochord is replaced by a cartilaginous or bony vertebral column. This statement is accurate therefore not the incorrect statement being sought for in the question.

Step 2: Evaluate statement B

In cephalochordates, the notochord is extended from head to tail region and is persistent throughout life. This statement is also accurate. Therefore, it too, is not the incorrect statement being sought for in the question.

Step 3: Evaluate statement C

Protochordates are exclusively marine. This statement is true because all members of the protochordates including urochordates and cephalochordates are found in marine habitats. Again, this is not the incorrect statement being sought for in the question.

Step 4: Evaluate statement D

Notochord is present in tail of adult in urochordata. This statement is incorrect because in the Urochordata, the notochord is only present in the larval stage. Therefore, this is the incorrect statement which the question is seeking.

Key Concepts

Vertebrates

Vertebrates are fascinating organisms that belong to the subphylum Vertebrata under the phylum Chordata. A key feature of vertebrates is the replacement of the notochord, a flexible rod-like structure, with a vertebral column during development. This vertebral column serves as a main support structure, protecting the spinal cord.
Vertebrates include a diverse range of animals such as fishes, amphibians, reptiles, birds, and mammals. As vertebrates evolved, they developed complex systems such as:

• Nervous systems, allowing sophisticated responses to environmental stimuli.
• Circulatory systems with well-developed hearts, providing efficient transport of nutrients and oxygen.
• Integumentary systems that include skin appendages such as feathers, scales, or hair.

These adaptations have allowed vertebrates to thrive in a variety of environments, from oceans to forests.

Cephalochordates

Cephalochordates, often known as lancelets, are small, fish-like marine animals. They are a group within the phylum Chordata and possess a number of distinct characteristics.
A prominent feature of cephalochordates is their persistent notochord that extends from head to tail throughout their life. Unlike vertebrates, cephalochordates maintain this structure rather than developing a vertebral column. It provides rigidity and support, aiding in locomotion.
Cephalochordates serve as important examples of primitive chordate characteristics and help scientists understand the evolution of more complex structures in vertebrates. They are:

• Filter feeders, using pharyngeal slits to trap food particles.
• Habituating shallow marine environments, usually buried in sand.
• Capable of simple swimming using their laterally flattened bodies.

Protochordates

Protochordates are a group of animals that bridge the gap between invertebrates and vertebrates within the phylum Chordata. This group includes both cephalochordates and urochordates.
Protochordates are exclusively marine, which means they inhabit oceanic environments. Despite their relatively simple structures, protochordates provide significant insight into evolutionary biology due to their primitive chordate features. They share some important traits:

• The presence of a notochord at some stage of their life cycle.
• Pharyngeal slits, which are openings used for filter feeding or respiration.
• A dorsal nerve cord, which provides primitive neural functions.

The study of protochordates continues to help scientists unravel the evolutionary pathway leading to complex vertebrates.

Urochordata

Urochordates, also known as tunicates, are another intriguing group within the phylum Chordata. They exhibit a fascinating transformation during their life cycle.
In their larval stage, urochordates possess a notochord and a tail, resembling small tadpoles. This notochord is not present in adults. As they mature, they undergo metamorphosis, during which they lose their notochord and tail, becoming sessile adults that resemble sacs attached to substrates.
Adult urochordates:

• Filter feed by pumping water through their bodies using siphons, capturing plankton and detritus.
• Have a unique covering called a tunic, composed of a cellulose-like substance.
• Are exclusively marine, thriving in diverse ocean habitats.

Their life cycle demonstrates both evolutionary simplicity and complexity, making them important subjects in evolutionary studies.