Problem 232 - Objective Biology for NEET

Question

Select the incorrect matching: [A: Phylum, B: Segmentation, C: Circulatory system, D: Distinctive features] [A: Absent, P: Present] A B \(\quad\) C \(\mathbf{D}\) (a) Ctenophore A A Comb plates for locomotion (b) Aschelminthes \(\quad\) A \(\quad\) P \(\quad\) Often worm shaped, elongated \(\begin{array}{llll}\text { (c) Annelid } & \text { P } & \text { P } & \text { Body segmentation like rings }\end{array}\) \(\begin{array}{llll}\text { (d) Arthropoda } & \text { P } & \text { P } & \text { Jointed appendages }\end{array}\)

Step-by-Step Solution

Answer

The incorrect matching is (b) Aschelminthes A P Often worm shaped, elongated. Aschelminthes have a circulatory system, which makes the given matching incorrect.

Step 1: Analyzing Phylum descriptions

First the individual aspects of each phylum are looked at, such as distinct features, presence or absence of segmentation, and the state of the circulatory system.

Step 2: Verification of Ctenophore

Ctenophores, also known as sea gooseberries or comb jellies, have a feature of comb plates for locomotion. It's accurate that they don't have segmentation, nor a circulatory system. Therefore, the first matching (a) is correct.

Step 3: Verification of Aschelminthes

Aschelminthes, many of them known as worms, are often elongated and worm-shaped. They do not have segmentation, but they do have a simple form of the circulatory system. So, the matching (b) is incorrect.

Step 4: Verification of Annelida

Annelids, commonly referred to as the ringed or segmented worms, do possess segmentation and a well-developed circulatory system. Hence, the matching (c) is correct.

Step 5: Verification of Arthropoda

Arthropoda, which includes insects, arachnids, myriapods, and crustaceans, are known for their jointed appendages. They show segmentation and do have a fully functioning circulatory system. So, the matching (d) seems to be right.

Key Concepts

Ctenophore

Ctenophores, often called comb jellies or sea gooseberries, are fascinating creatures found primarily in marine environments. They are unique due to their translucent bodies and the presence of comb plates. These comb plates are made of cilia, small hair-like structures that help the ctenophores move gracefully through water by beating in a coordinated fashion. Though they look similar to jellyfish, ctenophores lack the stinging cells that jellyfish possess.

Ctenophores do not exhibit segmentation, a common feature in more complex animals. They also do not have a circulatory system. Instead, nutrients and gases are exchanged directly through their body surface. This characteristic places them apart from more segmented and organized creatures found in other phyla. Understanding these basic attributes helps in identifying the uniqueness of ctenophores' place in the animal kingdom.

Aschelminthes

Aschelminthes, sometimes referred to as nematodes or roundworms, often have elongated and cylindrical bodies. Unlike some other phyla, these worms do not have segmented bodies. Their shape is somewhat reminiscent of an unsegmented tube.

One notable feature of Aschelminthes is their cuticle— a protective and flexible exterior layer. This cuticle is periodically shed as the worm grows, a process called molting. Aschelminthes have a simple circulatory system, which, instead of a heart, consists of a simple network of tubes that distribute nutrients. This trait is pivotal for their survival and helps them adapt to a variety of environments, from soil to bodies of water all over the world.

Annelida

Annelids, commonly known as segmented worms, include familiar creatures like earthworms and leeches. The segmentation of their bodies is their most distinguishable feature. It appears as a series of repetitive segments, which are most visible in creatures like earthworms.

Each segment of an annelid can contain repeated organs, which allows the organism a great degree of flexibility and resilience. Annelids also possess a well-developed circulatory system, complete with a series of hearts or a heart-like structure that pumps blood through their segmented bodies. This efficient circulatory system allows annelids to inhabit various environments, from deep ocean floors to moist terrestrial settings.

Arthropoda

Arthropods are the most diverse group in the animal kingdom, including insects, arachnids, crustaceans, and myriapods. The defining characteristic of Arthropoda is their jointed appendages—limbs that are segmented and articulated at intervals, allowing for complex movements.

Arthropods exhibit a hard exoskeleton made of chitin, which provides structural support and protection but must be periodically shed to allow for growth—a process known as molting. Inside, they show segmented body plans, akin to annelids but with greater complexity. Arthropods also have a well-developed circulatory system, typically an open system wherein the heart pumps blood into open spaces surrounding the organs. This adaptability has enabled arthropods to thrive in virtually every habitat on Earth, from ocean depths to cosmic heights.