Problem 241 - Objective Biology for NEET

Question

Assertion: The skeleton of sponges is made up of spicules. Reason: Composition of spicules help in classification of sponges.

Step-by-Step Solution

Answer

The skeleton of sponges is indeed made up of spicules and the composition of these spicules play a crucial role in the classification of sponges. Hence the reasoning is valid for the assertion.

Step 1: Understanding the Assertion

The first part of the problem is an assertion which says that the skeleton of sponges is made up of spicules.

Step 2: Understanding the Reason

The second part of the problem is a reason that claims that the composition of spicules help in the classification of sponges. Spicules comes in a variety of shapes and sizes, which can serve as an important phenotypic trait in sponges. Different types of sponges can have distinct spicules, and it's this variability that can help in classification.

Step 3: Validating the Reason for Assertion

Upon examining the assertion and the provided reason, we can see that the two are indeed related. It's correct that sponges' skeletons are formed up of spicules and that the varying compositions of these spicules help in distinguishing different types of sponges. Thus, the reason can be considered valid for the assertion.

Key Concepts

Spicules

Spicules are tiny structural elements that appear like needles. They can be composed of silica or calcium carbonate. These needle-like structures serve a key role in the makeup of a sponge's skeleton. Due to their diverse shapes and sizes, spicules are excellent distinguishing features in different species of sponges.

These structures, though microscopic, add rigidity and form to the sponge's body. In essence, spicules provide a framework that supports the sponge structure, much like bones do in vertebrates.

Understanding spicules is crucial because their composition and structure can tell us a lot about a sponge's classification and evolutionary adaptations.

Sponge Skeleton

The skeleton of sponges is an essential component that helps them maintain their shape and integrity in the water. The primary building blocks of this skeleton are the spicules.

This skeleton gives sponges their structural support. Depending on the type and arrangements of spicules, the texture and rigidity of a sponge can vary greatly. Some sponge skeletons are more rigid due to densely packed spicules, while others are more flexible due to a loose arrangement.

In some sponges, the spicules are cemented together by another substance called spongin, a type of collagen protein. This combination adds even more varieties to the sponge's texture and overall structural characteristics.

Classification of Sponges

Sponges belong to the phylum Porifera, and they are classified into different groups based on their spicules. The diversity in the composition, shape, and size of spicules allows scientists to classify sponges into major classes, such as Demospongiae, Calcarea, and Hexactinellida.

• Demospongiae: This class encompasses about 90% of all sponge species. They have a skeleton made primarily of spongin with silica-based spicules.
• Calcarea: Sponges in this class have spicules made of calcium carbonate. They typically live in shallow, tropical waters.
• Hexactinellida: Also known as glass sponges, these have a skeleton composed of silica, forming a glass-like lattice. They are mostly found in deep-sea environments.

The classification of sponges based on spicules is not only a way to organize them scientifically but also provides insights into their ecological roles and evolutionary history.