Problem 79 - Objective Biology for NEET

Question

The body of the aschelminthes is circular in cross section. Hence, it is named as (a) Tapeworm (b) Earthworm (c) Hookworm (d) Roundworm

Step-by-Step Solution

Answer

The correct answer is (d) Roundworm.

Step 1: Understand the prominent characteristic

First off, the key characteristic given here is that the body of the worm is 'circular in cross section'. This refers to the shape of the worm's body when it is cut perpendicular to its length. So, the focus is on identifying which worm out of the given options has a body that, when cut, would appear circular.

Step 2: Apply known facts

Next, each of the options (Tapeworm, Earthworm, Hookworm, Roundworm) is analyzed based on what is known about their body structures. Tapeworms are flat, not round in cross section. Earthworms have a cylindrical body, but they are not aschelminthes. Hookworms are also not round in cross-section.

Step 3: Confirm the right option

By process of elimination, we are left with Roundworm, which, as its name suggests, is round in cross section. So, (d) Roundworm is the correct choice.

Key Concepts

Cross Section

The term "cross section" refers to the shape of an object when it is sliced perpendicular to its length. Imagine cutting through a tube or a pipe; the exposed shape you see is its cross section. For living organisms like worms, the cross section can tell us a lot about their physical structure.

In the case of Aschelminthes, a phylum where roundworms belong, their cross section when viewed would appear circular. This is distinct from other types which might be flat or oblong. Understanding the cross section helps differentiate these creatures from others. For instance:

• Tapeworms, known for being flat, have an elongated sheet-like cross section.
• Earthworms, although cylindrical, have a slightly flattened cross-section compared to roundworms.

This circular characteristic of Aschelminthes aids in their movement and interaction with their habitat.

Roundworm

Roundworms, scientifically referred to as "Nematodes," are a massive group of worms found in various environments. They are a subset of the Aschelminthes and are characterized mainly by their round cross-sectional shape.

These worms are incredibly diverse, inhabiting soils, freshwater, and marine ecosystems. Some even function as parasites in plants and animals. Notable features of roundworms include:

• A simple, tubular digestive system that runs from mouth to anus.
• A flexible, durable outer cuticle that can be shed as they grow.
• The absence of a segmented body, unlike earthworms or annelids.

Despite their simplicity, roundworms play essential roles in the ecosystem, such as nutrient recycling and soil aeration.

Body Structure

The body structure of aschelminthes, particularly roundworms, is pivotal to understanding their adaptability and function. Typically, these worms have:

• An unsegmented, elongated body that is tapered at both ends.
• A pseudocoelom, which is a fluid-filled body cavity that acts as a hydrostatic skeleton, providing them support and enabling movement.
• A complete digestive system with a distinct mouth and anus, unlike some simpler organisms.

The muscular and skeletal systems are highly simplified, relying on the pressure of fluids within the pseudocoelom for maintaining shape and muscle function. This body structure allows them to survive in various environments and contribute significantly to biological ecosystems, including serving as parasites to larger hosts where they can impact health and agriculture.