Question

Given a diagram showing the different stages in the process of fertilization of an egg in the human female reproductive tract.
Study the diagrams and answer the question
Arrange the letters given, each diagram in a logical sequence to show the correct order in the process of fertilization.

Answer 1

The sperm which reaches the ovum first is responsible for inhibiting the entry of other sperms into the ovum by the action of the zona pellucida layer of ovum leaving the polar body inside and disintegrating.

Complete answer:
Fertilization is a process in which the sperm which is the male part and the ovum which is the female part of the human interacts together to form the zygote and eventually forming the embryo giving birth to a human baby.

The sperm consist of a tail part and the protein head which contains the genetic material of man. The tail helps in the quick movement and swimming of the sperm through the vagina and fallopian tube of the female reproductive organ.

Ovum is also the egg with which the sperms fuse and the ovum is protected by many layers among which the outer layer is known as zona pellucida it is the layer with which the sperms first come in contact and as soon as the first sperm comes in contact with the zona pellucida the entry of other sperms is prohibited as there is only one egg to fuse with. When the entry of other sperms is rejected then the sperm which reached there first makes its way through the outer membranes of the ovum and thus releasing the protein head into the cytoplasm of the ovum. During the course of time the tail of current sperm and the other sperms disintegrate.

As visible from the images the first sequence is when the egg is alone without any sperms, followed by then reaching of sperms to ovum, then one of the sperm heads crosses the membranes and enters the cytoplasm leaving the head into the cytoplasm and disintegrated tails and sperms cannot be seen.

Hence, the correct answer is D, C, B, and A.

Note: The no. of sperms released into the female vagina are in million of numbers and amongst these only few of them reaches the ovum due to action of the immune system of females. Here in the figure the first and last one are different as the first figure is holding the protein head of the sperm and the last image is showing only the female polar body of the ovum which is ready to be fertilized.