Problem 23 - Objective Biology for NEET

Question

Which of the following is correct about metamerism (true segmentation)? (a) Every organ shows serial repetition. (b) The body is divided externally as well as internally (c) Each segment is not supplied with separate nerve and blood vessels. (d) All of these

Step-by-Step Solution

Answer

The correct statement about metamerism is: The body is divided externally as well as internally.

Step 1: Understand Metamerism

Metamerism (or true segmentation) represents a form of organization where the body of an organism is divided into a series of similar parts, segments, which are arranged in linear sequence. This is a common characteristic for some species in the animal kingdom, like earthworms.

Step 2: Evaluate Each Statement

Evaluate each provided option against the definition and characteristics of metamerism. (a) Every organ shows serial repetition - This is not particularly correct, not all organs show repetition in segmented organisms.(b) The body is divided externally as well as internally - This is true for metamerism where the repetition can be seen both externally and internally.(c) Each segment is not supplied with separate nerve and blood vessels - This is incorrect. In segmentation, each segment often has its own set of body structures including nerves and blood vessels.(d) All of these - Since not all of the previous statements are correct, this option is also incorrect.

Step 3: Choose the Correct Answer

Based on the evaluation in Step 2, the correct statement about metamerism is: The body is divided externally as well as internally.

Key Concepts

Segmentation

Segmentation in biology, often referred to as metamerism, is a fascinating aspect of organismal structure. It involves the division of an organism's body into repeated sections, called segments. These segments can be observed both externally and internally in certain organisms.

Metamerism allows for specialization within each segment, enabling different parts of the organism to perform unique functions. For example, one segment might be adapted for locomotion while another specialized for reproduction.

In addition to this functional specialization, segmentation can aid in the growth and development of an organism. Parts can be added or removed with fewer impacts on the whole organism, offering an evolutionary advantage.

Animal Kingdom

The animal kingdom showcases a diversity of life forms, and segmentation is one feature that appears in various phyla. Metamerism is particularly common among annelids, arthropods, and chordates.

Although the appearance and function of segmented bodies vary across the animal kingdom, this organization can lead to greater flexibility and efficiency in movement and function.

• Annelids: Earthworms, for instance, display visible segments that aid in their burrowing lifestyle.
• Arthropods: Insects and other arthropods have segments that can form distinct body regions like the head, thorax, and abdomen.
• Chordates: Segmentation is apparent in the spine of vertebrates.

Segmentation offers adaptive advantages that can drive evolutionary success and diversification.

Earthworms

Earthworms are an exemplary model of segmentation within the animal kingdom. Each segment of an earthworm is known as a "metamere," and these are serially repeated along their elongated body.

Such segmentation provides earthworms with flexibility and strength as they move and burrow through soil. Each metamere contains repeated organs - such as excretory organs, nerve sets, and sometimes even segments specific to reproduction.

The segmentation in earthworms allows them to have a structured response to environmental stimuli. As they move, their muscles contract and expand, enabling them to push through soil effectively. Moreover, if an earthworm loses a segment, it can sometimes regenerate, showcasing the resilience offered by metamerism.

Organism Organization

Organization within an organism, especially in terms of segmentation, enhances its efficiency and specialization. This type of structural arrangement means an organism can manage multiple functions simultaneously.

• Efficiency: Segments allow for the better allocation of resources and energy, optimizing the organism's functionality.
• Specialization: Different segments can have specialized organs tailored to specific tasks, increasing the organism's ability to adapt to environmental challenges.
• Developmental Flexibility: Segmentation allows for the evolution of complex body plans, enabling transitions from simple to more complex organisms over time.

Ultimately, segmented organization represents a sophisticated biological strategy, emphasizing nature's inclination towards balance and efficiency in survival and reproduction.