Chapter 29, Problem 7STP

Summary Introduction

Introduction:

Reptiles are fully adapted to life on land and were the first completely terrestrial vertebrates. The characteristics that allow reptiles to succeed on land include a shelled egg, scaly skin, and more efficient circulatory and respiratory systems.

Answer to Problem 7STP

Correct answer:

The correct answer is option (B) 2.

Explanation of Solution

Explanation/justification for the correct answer:

Option (B) 2. The option 2 represents yolk sac. The yolk sac is a membranous sac attached to the embryo, produced by the hypoblasting cells adjacent to the embryonic disc. The embryo is self-sufficient because it gets its nutrients from food in the yolk sac inside the egg. So, the correct answer is option (B).

Explanation for incorrect answer:

Option (A) 1. The option 1 represents amnion. An amnion is a membrane that surrounds a developing embryo. It is filled with fluid that protects the embryo during development. So, this is an incorrect option.

Option (C) 3.The option 3 represents allantois. An allantois is a membrane that develops a sac that carries wastes produced by the embryo. So, this is an incorrect option.

Option (D) 4. The option 4 represents leathery shell. The leathery shell is the fluid-filled membrane. The leathery shell of amniotic egg can protect the internal fluids and embryo, and keep it from drying out during development. So, this is not the correct option.