Identify the statements which are correct with respect to fertilization.
(A) Sperm comes in contact with zona pellucida layer of the ovum
(B) Acrosome secretions help the sperm to pass through the cells of corona radiata
(C) Entry of sperm into the cytoplasm of ovum induces the completion of the meiotic division of the secondary oocyte
(D) Fertilization can occur if the ovum and sperms are transported simultaneously to the ampullary region
Choose the correct answer from the options given below.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (C) and (D) only
(A) Sperm comes in contact with zona pellucida layer of the ovum Correct. During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum. This contact changes the membrane so that no other sperm can enter, and only one sperm fertilises the ovum.
(B) Acrosome secretions help the sperm to pass through the cells of corona radiata Incorrect. The secretions of the acrosome help the sperm enter the cytoplasm of the ovum through the zona pellucida and the plasma membrane. NTA has put “corona radiata” in place of the book’s “zona pellucida”, and that change of words makes the statement false.
(C) Entry of sperm into the cytoplasm of ovum induces the completion of the meiotic division of the secondary oocyte Correct. The ovum is released as a secondary oocyte that has not finished meiosis. The entry of the sperm makes it complete the second meiotic division, which forms a second polar body and a haploid ovum (ootid).
(D) Fertilization can occur if the ovum and sperms are transported simultaneously to the ampullary region Correct. Fertilisation takes place in the ampullary region of the fallopian tube. It can only occur if the ovum and the sperms reach it at the same time. That is why not every copulation leads to pregnancy.
NCERT Extract:
Fertilisation and Implantation – “… The process of fusion of a sperm with an ovum is called fertilisation. During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum (Figure 2.10) and induces changes in the membrane that block the entry of additional sperms. Thus, it ensures that only one sperm can fertilise an ovum. The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. This induces the completion of the meiotic division of the secondary oocyte.”