Body Symmetry Types in Animals — NEET Biology
📚 Practice ConceptAnimals can be categorised on the basis of their symmetry. Sponges are mostly asymmetrical, i.e., any plane that passes through the centre does not divide them into equal halves. When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry. Coelenterates, ctenophores and echinoderms have this kind of body plan. Animals like annelids, arthropods, etc., where the body can be divided into identical left and right halves in only one plane, exhibit bilateral symmetry.
Which of the following statements about body symmetry in animals are correct? S1. Sponges are typically asymmetrical, meaning no plane passing through the center divides them into equal halves. S2. Coelenterates and Ctenophores exhibit radial symmetry, where any plane through the central axis divides the organism into identical halves. S3. Adult Echinoderms display bilateral symmetry, while their larval forms are radially symmetrical. S4. Animals like Annelids and Arthropods exhibit bilateral symmetry, characterized by identical left and right halves in only one plane. S5. In radially symmetrical animals, directional movement is highly efficient due to a distinct anterior end.
View solution & NCERT explanation
Correct answer: B — S1, S2 and S4 only
Let's evaluate each statement based on NCERT: S1. Correct. Sponges are described as mostly asymmetrical in the NCERT text. (NCERT: "Sponges are mostly asymmetrical, i.e., any plane that passes through the centre does not divide them into equal halves.") S2. Correct. Coelenterates and ctenophores are classic examples of radially symmetrical animals. (NCERT: "When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry. Coelenterates, ctenophores and echinoderms have this kind of body plan.") S3. Not correct. The symmetry is reversed in this statement. Adult echinoderms are radially symmetrical, while their larvae are bilaterally symmetrical. (NCERT: "The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.") S4. Correct. Annelids and Arthropods are examples of bilaterally symmetrical animals. (NCERT: "Animals like annelids, arthropods, etc., where the body can be divided into identical left and right halves in only one plane, exhibit bilateral symmetry.") S5. Not correct. Efficient directional movement and a distinct anterior end are characteristic features of bilateral symmetry, not radial symmetry, which typically suits sessile or floating lifestyles. (NCERT does not explicitly state this, but implies it by association of bilateral symmetry with more advanced, motile forms.) Therefore, statements S1, S2, and S4 are correct. The final answer is B.
What does NCERT say about Animals can be categorised?
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