Question

Explain how fertilization takes place in human beings. (With diagram)

Answer 1

During copulation semen released from penis into the vagina(insemination). Motile sperms swim rapidly through cervix and moves to uterus and finally reach the ampullary-isthmus junction of Fallopian tube. Ovum released from ovary also reached to this junction where fertilization will take place. An important thing to be noted that if ovum and sperm simultaneously transported to this junction then fertilization occur if this doesn't happen then the copulation will not lead to successful fertilization. The process of fusion of a sperm and an ovum is called as fertilization.

Now comes the most important part of this whole process. when sperm comes in contact with the ovum it induces certain changes in the membrane zona pellucida of ovum that blocks the entry of additional sperms. It ensures that only one sperm fuse with the ovum. Acrosomal secretions also play important role in entry of sperm into the cytoplasm of ovum through the zona pellucida layer and plasma membrane. It result in the completion of meiotic division of secondary oocyte. The second meiotic division is also unequal and results in formation of second polar body and a haploid ovum. As a result this ovum fuses with the nucleus of sperm (haploid) forming a zygote(diploid).