Assertion: When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry.
Reason: Sponges mostly show radial symmetry.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) -Assertion is correct but reason is incorrect.
Animals 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.