Which one of the following statement is totally wrong about the occurrence of notochord, while the other three are correct ?

Question

Accepted Answer

Option 3 is stated as the correct answer, which claims that the notochord is not persistent throughout life in chondrichthyes. Let's explore why this statement is considered totally wrong and why the other options are correct:

1. **Explanation for Option 3:**
   - Chondrichthyes, which include sharks, rays, and skates, are a class of cartilaginous fish. In these animals, the notochord is indeed persistent throughout their life. It is not replaced by a vertebral column as in many other vertebrates. Instead, the notochord is surrounded by cartilaginous structures, which provide support and flexibility. Therefore, the statement that the notochord is not persistent throughout life in chondrichthyes is incorrect, making Option 3 the right choice for the statement that is totally wrong.

2. **Explanation for Option 1:**
   - The statement that the notochord is present only in the tail of ascidian larva is correct. Ascidians, or sea squirts, are urochordates, and their larvae possess a notochord that is restricted to the tail region. This notochord is lost during metamorphosis into the adult form, which does not have a notochord.

3. **Explanation for Option 2:**
   - The statement that the notochord is replaced by a vertebral column in adult toads is correct. In amphibians like toads, the notochord is present during the embryonic stage but is replaced by a vertebral column as the animal matures into an adult.

4. **Explanation for Option 4:**
   - The statement that the notochord persists throughout life in Amphioxus and extends from head to tail is correct. Amphioxus, or lancelets, are cephalochordates, and they retain the notochord throughout their life. It extends the entire length of the body, from head to tail, providing structural support.

In summary, Option 3 is the correct choice for the statement that is totally wrong because it inaccurately describes the persistence of the notochord in chondrichthyes. The other options correctly describe the occurrence and fate of the notochord in the respective organisms.