Question

Given below is the diagram of human ovum surrounded by a few sperms. Observe the diagram and answer the questions that follows:

1. Compare the fate of sperms ‘P’, ‘Q’ and ‘R’ shown in the diagram.
2. Write the role of Zona pellucida in this process.
3. Analyse the changes occurring in the ovum after the entry of sperm.
4. How acrosome and middle piece of a human sperm are able to play an important role in human fertilization?

Answer 1

1. Sperm P: This sperm seems to be breaking through the ovum's (egg) outer covering, the zona pellucida. Sperm P is probably going to fertilize the ovum.
   Sperm Q: The corona radiata cells that surround the zona pellucida contain this sperm. Sperm Q will probably finally make it to the zona pellucida and try to fertilise it.
   Sperm R: The corona radiata does not include this sperm. Sperm R might make it to the ovum, but it might not be able to enter and fertilize the egg.
2. Role of Zona Pellucida in Fertilisation: By blocking the admission of additional sperm once one sperm has entered, the zona pellucida promotes species-specific sperm binding and avoids polyspermy.
3. Changes in the ovum after sperm entry: To stop multiple sperm entrance, the zona pellucida hardens.
   Completion of meiosis II: After completing meiosis, the secondary oocyte forms the second polar body and the ovum.
   Formation of male and female pronuclei: The female nucleus merges with the decondensed sperm nucleus.
4. Role of acrosome and middle piece in fertilisation:
   Acrosome: It includes the enzymes acrosin and hyaluronidase, which break down the zona pellucida to allow sperm access.
   Middle piece: It has mitochondria, which give sperm the ATP they need to move and reach the ovum.