Which part of the sperm plays an important role in penetrating the egg membrane?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Acrosome
A human sperm has a head, a neck, a middle piece and a tail. The head carries a haploid nucleus, and the front part of the nucleus is covered by a cap-like structure, the acrosome. The acrosome holds enzymes. At fertilisation these secretions let the sperm pass through the zona pellucida and the plasma membrane of the ovum.
Option (1) Tail — Incorrect. The tail moves the sperm forward, using energy from the mitochondria of the middle piece. It gives motility, but it does not dissolve the egg membranes.
Option (2) Acrosome — Correct. The acrosome is filled with enzymes that help fertilisation. Its secretions help the sperm enter the cytoplasm of the ovum through the zona pellucida and the plasma membrane.
Option (3) Allosome — Incorrect. An allosome is a sex chromosome. In the sperm it lies inside the nucleus as part of the chromosomal material, so it plays no part in getting through the egg membranes.
NCERT Extract:
Gametogenesis – “… Let us examine the structure of a sperm. It is a microscopic structure composed of a head, neck, a middle piece and a tail (Figure 2.6). A plasma membrane envelops the whole body of sperm. The sperm head contains an elongated haploid nucleus, the anterior portion of which is covered by a cap-like structure, acrosome. The acrosome is filled with enzymes that help fertilisation of the ovum.”
Fertilisation and Implantation – “… The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane.”
Figure 2.6 Structure of a sperm