Question

Given below are two statements:
Statement I : When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry.
Statement II : In phylum Echinodermata, both adults and larvae are radially symmetrical.
Choose the most appropriate answer.

• A. Statement I is incorrect but Statement II is correct
• B. Both Statement I and Statement II are correct
• C. Both Statement I and Statement II are incorrect
• D. Statement I is correct but Statement II is incorrect

Hint:

Echinoderm symmetry trick: Larva = Bilateral symmetry Adult = Radial symmetry Do not confuse both stages.

Answer 1

The Correct Option is D

Concept: Symmetry in biology refers to arrangement of body parts relative to an axis or plane. Radial symmetry occurs when many planes passing through central axis divide organism into similar halves. Echinoderms show an interesting developmental pattern. Adults are radially symmetrical whereas larvae are bilaterally symmetrical. Thus one statement may be correct while another may be false.

Step 1: Understand radial symmetry definition.
Radial symmetry means body parts arranged around a central axis. Any plane passing through central axis divides organism into similar halves. Examples include starfish and jellyfish. The definition given in Statement I correctly explains radial symmetry. Hence \[ Statement\;I=\text{Correct} \]

Step 2: Understand symmetry in echinoderms.
Echinodermata includes starfish, sea urchins and sea cucumber. Adult echinoderms possess radial symmetry. However larvae do not show radial symmetry. Larvae are bilaterally symmetrical. This difference is important in evolutionary biology.

Step 3: Evaluate Statement II carefully.
Statement II says both adult and larval forms are radially symmetrical. This is incorrect because larval forms are bilateral. Thus statement II is false. \[ Statement\;II=\text{Incorrect} \]

Step 4: Determine correct option.
Final conclusion: Statement I → Correct Statement II → Incorrect Hence correct option is \[ \boxed{\text{Option (4)}} \]