Assertion: Cephalization is first observed in Phylum Platyhelminthes.

Reason: Cephalization developed along with the evolution of bilateral symmetry.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Cephalization refers to the concentration of sensory organs and nervous tissue at the front end of an organism, which is a key feature of more complex animals. In the case of Phylum Platyhelminthes, or flatworms, cephalization is indeed first observed. This development is closely linked to the evolution of bilateral symmetry, where the body plan is organized along a central axis, allowing for a distinct head region.

Analysis of the Statements

Let's break down the assertion and reason:

• Assertion: Cephalization is first observed in Phylum Platyhelminthes. This is true.
• Reason: Cephalization developed along with the evolution of bilateral symmetry. This is also true.

Connecting the Dots

The reason provided accurately explains why cephalization occurs in organisms with bilateral symmetry, including flatworms. Therefore, both statements are correct, and the reason effectively supports the assertion.

Final Answer

The correct choice is A: Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.