Chapter 24, Problem 4A

Summary Introduction

Introduction :

Different animals have different features in their feeding process, development of their body, and the features that involve as their support in the body structure. Some of the animals are invertebrates and it includes all the animals that have exoskeletons. The exoskeletons is the outer coverage of the body, it is the tough or hard outer cover, it provides support to the soft tissue of the body, avoid loss of water, and also give protection against predators. The endoskeleton is the internal covering of some of the vertebrates. It includes sea stars and sea urchins; they are made of calcium carbonate, cartilage, etc. Unlike different cell structure different animals have different reproductive structure. One of the features includes hermaphrodites, the animals that produce both sperms and egg. They produce egg and sperm simultaneously with the help of sexual reproduction. In many animals the zygote undergoes mitotic cell division and form two cells that are termed as embryo. The division of embryonic cell continueto form blastula. Animals like frogs undergoes further division of cell to form gastrula.

Answer to Problem 4A

Correct answer :

The correct answer is option (A) gastrula.

Explanation of Solution

Explanation/justification for the correct answer :

Option (A) gastrula. The gastrula is the stage of embryonic development. The gastrula is developed due to the continued division of blastula. It is double layered sac with an opening at one end.So, the correct answer is option (A).

Explanation for incorrect answer :

Option (B)blastula. In many animals the zygote undergoes mitotic cell division and form two cells that are termed as embryo. The division of embryonic cell continueto form blastula. In this stage the number of cytoplasm remain same in the embryo. So, this is an incorrect option.

Option (C) egg cell. The egg cells seem as one cytoplasm with the nucleus in the center.So, this is an incorrect answer.

Option (D) zygote. The egg undergo fertilization after the penetration of sperm inside the female and forms the zygote.So, this is an incorrect answer.