Problem 107 - Objective Biology for NEET

Question

Bilaterally symmetrical, triploblastic, segmented, coelomate and covered by chitinous exoskeleton are features of (a) Anneldia (b) Vertebrata (c) Amphibia (d) Arthropoda

Step-by-Step Solution

Answer

The Arthropoda have all the features mentioned in the exercise, including being bilaterally symmetrical, triploblastic, segmented, coelomate, and covered by a chitinous exoskeleton. The correct answer is (d) Arthropoda.

Step 1: Understanding Term Definitions

First off, it is essential to understand these terms: Bilaterally symmetrical refers to organisms which can be divided along a sagittal plane into two mirror images. Triploblastic describes organisms with three germ layers: endoderm, mesoderm, and ectoderm. A coelomate is an organism with a coelom (body cavity lined with mesoderm). Chitinous exoskeleton is a hard outer covering made of chitin.

Step 2: Analyzing the Options

Next, analyze each option in the exercise:\n\n(a) Anneldia: Although this phylum is bilaterally symmetrical, triploblastic, segmental and coelomate, the organisms do not possess a chitinous exoskeleton. \n\n(b) Vertebrata: These are bilaterally symmetrical, triploblastic and coelomate. However, this group is characterized by a vertebral column and internal skeleton, rather than segmented body and chitinous exoskeleton. \n\n(c) Amphibia: Being part of the vertebrates, Amphibia also have bilateral symmetry, are triploblastic and coelomate. Again, however, these organisms lack a chitinous exoskeleton. \n\n(d) Arthropoda: This phylum consists of organisms which are bilaterally symmetrical, triploblastic, have segmented bodies, are coelomate, and possess a chitinous exoskeleton.

Step 3: Solution

From the above analysis, it is clear that Arthropoda possess all the characteristics mentioned in the question.

Key Concepts

Bilaterally Symmetrical Organisms

Bilateral symmetry is a fascinating concept in biology, referring to organisms that have body structures which can be divided into identical halves on either side of a unique plane, known as the sagittal plane. Think of it like splitting an apple into two even halves; each side is a mirror image of the other. Arthropods, such as insects, spiders, and crustaceans, fall under this category, showcasing this symmetry in their body organization. This feature helps them move effectively and respond to their environment efficiently as it allows for streamlining, which is particularly helpful during movement, and it also aids in developing a complex nervous system.

Triploblastic Organisms

Diving deeper into the development of organisms, triploblastic organisms are those that can boast of having three distinct germ layers formed during embryogenesis. These layers are the ectoderm, mesoderm, and endoderm, each with its own unique contribution to the body's structure and functions. The ectoderm forms the skin and nervous system, the mesoderm contributes to muscles and the circulatory system, while the endoderm develops into the internal organs like the gut. Arthropods are triploblastic, which means they have a complex body structure that allows for specialized tissues and organs.

Coelomate Animals

When we talk about a coelom, we're referring to a fluid-filled body cavity found in coelomate animals. This cavity is lined with a tissue called mesoderm, which also surrounds the internal organs. The presence of a coelom is incredibly beneficial for these creatures as it not only provides room for organ development and movement but also functions as a sort of 'cushion' to protect organs from external shocks or pressures. Arthropods are enriched with this feature, which helps support their elaborate organ systems.

Chitinous Exoskeleton

Finally, one of the standout characteristics of arthropods is their chitinous exoskeleton. 'Chitin' is a tough, flexible substance that provides external support and protection for these organisms, much like a knight's armor. Unlike humans and other vertebrates that have internal bone structures for support (endoskeletons), arthropods rely on this external shell not only for protection against predators and environmental hazards but also as an attachment point for muscles. Moreover, it's integral for their growth as they molt or shed this exoskeleton to increase in size – a process known as ecdysis.