Chapter 24, Problem 30A

Summary Introduction

Introduction :

Cnidarians and sponges were the first animals that evaluated from a multicellular ancestor. Most sponges live in marine water. Sponges have no tissues, no organs, and most have no symmetry. Sponges belong to the phylum Porifera that contains between 5000 to 10000 members.

Answer to Problem 30A

Correct answer :

The correct answer is option (B) external fertilization.

Explanation of Solution

Explanation/justification for the correct answer :

Option (B) external fertilization. External fertilization is a different form of fertilization where fertilization occurs outside the mother cell. Jellyfishes release eggs and sperms in the medusa stage into water where fertilization occurs. So, the correct answer is option (B).

Explanation for incorrect answer :

Option (A) fragmentation. Sponges can reproduce asexually by fragmentation, budding, or gemmules. Through fragmentation, a piece of sponge that is broken off as a result of a storm or other occurrence becomes a new adult sponge. The given diagram is a jellyfish which belongs to cnidarians. So, this is an incorrect option.

Option (C) internal fertiliozation. Jellyfishes release eggs and sperm in the medusa stage into water where fertilization occurs. This type of fertilization is known as external fertilization. So, this is an incorrect answer.

Option (D) regeneration. Regenaration is a process of coming back, growing into a new individual or rebirth. A jellyfish can reproduce by external fertilization. So, this is an incorrect answer.