Problem 2 - Objective Biology for NEET

Question

Which is not a character of sponges? (a) Multicellular (b) Cells are functionally independent (c) Cellular level of organization (d) Tissue level of organization

Step-by-Step Solution

Answer

The characteristic that does not apply to sponges is (d) Tissue level of organization.

Step 1: Understanding the structure of sponges

Sponges are multicellular organisms (choice a), and their cells simultaneously perform several functions. This independence of cells means that sponges do not need a system of organs for survival (choice b). Sponges are the simplest form of mult-cellular animals, and they have a cellular level of organization (choice c). This means their cells are specialized but do not form tissues or organs.

Step 2: Elimination based on knowledge of sponges

Based on the details discussed in step 1, all options except (d) Tissue level of organization align with the characteristics of sponges. Sponges do not have tissues; instead, they have specialized cells for different tasks. Therefore, the option (d) Tissue level of organization is not a character of sponges.

Key Concepts

Multicellularity in Organisms

Most organisms we commonly observe are made up of more than one cell; they are termed multicellular organisms. Unlike unicellular organisms, which consist of a single cell, multicellular life forms are composed of many cells that perform various functions. For example, the cells in a human body are organized into tissues such as muscle and nervous tissue, which are then arranged into organs and organ systems.

In contrast, sponges represent a basic level of cellular organization. Despite being multicellular, the cells within a sponge work more independently compared to those in more complex organisms. Each cell in a sponge has the ability to perform several functions necessary for the organism’s survival, such as digestion, waste removal, and even reproduction.

This type of organization is fascinating from a biological standpoint, because it shows how life can exist and thrive even without the complex systems seen in higher animals. Sponges, with their unique organization, provide insight into the evolution of multicellularity, suggesting a gradual increase in complexity from single cells to complex multicellular organisms like animals and plants.

Cellular Level of Organization

Beyond being just multicellular, life forms exhibit varying degrees of complexity in terms of cellular organization. The cellular level of organization is a pivotal concept in understanding different life forms.

In sponges, the cells are not organized into true tissues or organs, but they still display specialization. Some sponge cells have microvilli for feeding, others are involved in structural support, and there are also cells responsible for distributing nutrients.

These cells work together as a loose federation, each contributing to the overall function of the organism without the strict interdependence found in more advanced organisms. This level of organization is simple and yet remarkably effective for the ecological niches that sponges occupy. It also provides an excellent example of how, at a basic level, cells can work together for a common goal without the sophisticated organization found in other multicellular organisms.

Absence of Tissue in Sponges

One distinct characteristic of sponges is their absence of true tissues. Tissues are groups of specialized cells that work together to carry out specific functions. In most animals, tissues are the building blocks for more complex structures like organs and organ systems. However, sponges operate differently.

Since sponges do not have tissues, their cells must perform the necessary physiological functions independently or in a semi-coordinated fashion. This simplicity is a key trait of poriferans – the phylum to which sponges belong. Their bodies are organized into distinct layers, yet these do not form true tissues, revealing an evolutionary stage where multicellularity exists without the tissue-level organization seen in most other animals.

Understanding this unique aspect of sponge biology helps clarify why the option (d) 'Tissue level of organization' from the exercise does not apply to sponges and therefore, is the correct answer to the question. This knowledge allows us to appreciate the diverse ways life can be structured, and how even simple organisms are perfectly suited to their roles in nature.