Chapter 18, Problem 1A

Summary Introduction

Introduction:

The reproductive system of the human body has a role in producing gametes (sperm and egg cells) for producing a new individual. This is called as a process of fertilization.

Answer to Problem 1A

Correct answer:

A single sperm enters an egg only because the changes occur in the zona pellucida. Therefore, option (c) is correct.

Explanation of Solution

Reason for the correct statement:

Fertilization is a process where there is union of an egg and a sperm for the formation of a zygote. There are certain steps in the process of fertilization. One of them is when the sperm enters the egg. As there is entry of the sperm cell into the egg cell, the zona pellucida becomes the membrane for fertilization after certain changes.

Option (c) is given as “changes occur in the zona pellucida”.

“Only a single sperm enters an egg because changes occur in the zona pellucida”, it is the right answer.

Hence, option (c) is correct.

Reasons for the incorrect statements:

Option (a) is given as “sperm have an acrosome”.
The sperms possess an acrosome that consists of the digestive enzymes. So, it is a wrong answer.

Option (b) is given as “corona radiata gets larger”.
A single sperm cell enters the corona radiata (adhering follicular cells) that surrounds the zona pellucida. It does not become large. So, it is a wrong answer.

Option (d) is given as “the cytoplasm hardens”.
The cytoplasm does not harden when the sperm nucleus enters the oocytes cytoplasm. So, it is a wrong answer.

Option (e) is given as “All of these are correct”.
As only one sperm can enter an egg because the changes occur in the zona pellucida and it not depend on other factors. So, it is a wrong answer.

Hence, options (a), (b), (d) and (e) are incorrect.

Conclusion

:

Only a single sperm enters an egg because changes occur in the zona pellucida layer.