Problem 45 - Objective Biology for NEET

Question

The following characters are related to phylum: (1) Aquatic, mostly marine (2) Sessile or free swimming (3) Radially symmetrical animals (4) They show polymorphism (a) Porifera (b) Ctenophora (c) Echinodermata (d) Coelenterata

Step-by-Step Solution

Answer

The correct answer is (d) Coelenterata.

Step 1: Review Characteristics of Phyla

In order to proceed, you must know the features of the given phyla. For instance, organisms in the phylum Porifera are sessile and asymmetrical; those in Ctenophora are marine, mostly free-swimming, and display radial symmetry. Echinoderms are also marine, display radial symmetry, but are bottom dwelling and show no polymorphism. Lastly, Coelenterata include organisms that are aquatic (mostly marine), can be either free-swimming or sessile, show radial symmetry, and exemplify polymorphism with the presence of polyps and medusae in their bodies.

Step 2: Matching Characteristics

The given features primarily match with the characteristics of the phylum Coelenterata. They are mostly marine, can be either sessile or free-swimming, they show radial symmetry, and they definitely exhibit polymorphism.

Step 3: Choose the Correct Phylum

Having identified the phylum that fits the described characteristics, the correct option is (d) Coelenterata.

Key Concepts

Radial Symmetry in Animals

Radial symmetry in animals is a form of body symmetry where similar parts of an organism are arranged and repeated around a central axis. Imagine cutting a pie - any cut through the middle will yield roughly equal halves. This arrangement allows creatures to interact with their environment in all directions equally and is mainly seen in sessile or slow-moving organisms, as it facilitates feeding and defense from predators.

Sea anemones, jellyfish, and other cnidarians exhibit radial symmetry, aligning with their often sessile nature or their free swimming, drifting lifestyle in aquatic habitats. This symmetry is advantageous for animals like those in the phylum Coelenterata, as their life processes do not favor a particular direction.

Polymorphism in Aquatic Organisms

Polymorphism is a biological phenomenon where two or more different forms, or morphs, exist in the same population of a species. In aquatic organisms, it often relates to the life cycle stages that are adapted to varying ecological niches. For instance, the phylum Coelenterata includes organisms like jellyfish and corals that exhibit polymorphism significantly. They possess two major body forms - the sessile polyp and the free-floating medusa.

Significance of Polymorphism

Polymorphism in aquatic organisms is critical for adapting to diverse habitats, broadening food sources, avoiding competition, and escaping predators. By altering their body forms, these organisms can maximize their survival and reproductive success in changing environments.

Aquatic Habitats of Marine Species

The aquatic habitats of marine species are incredibly diverse, ranging from the shallow sunlit waters of coral reefs to the dark abyss of the ocean depths. Phylum Coelenterata members, such as jellyfish, sea anemones, and coral, typically reside in saltwater environments and adapt to various zones within these ecosystems.

Variety in Marine Habitats

Some coelenterate species are stationary and attach to rocks or coral reefs, benefiting from abundant sunlight and oxygen. Others float or swim in the open ocean, utilizing currents for movement and feeding. The diversity in aquatic habitats demands a versatile set of survival strategies, which is why many marine species exhibit such varied and complex life cycles.

Biological Classification for NEET

Biological classification is a critical topic for NEET (National Eligibility cum Entrance Test), an exam for students aspiring to enter medical fields in India. It deals with the systematic arrangement of living organisms into hierarchical groups based on their similarities and evolutionary relationships.

In this context, understanding phyla such as Coelenterata is essential. For NEET, students must be well-versed in the distinguishing characteristics of each phylum, such as habitat types (aquatic, marine), body symmetry (radial, bilateral), cell organization (tissue, organ), and reproductive and feeding structures. Mastery of these details forms the basis for understanding the complexity of life and evolutionary biology, which is fundamental in medical studies.