Sperm is a microscopic structure composed of a head, neck, middle piece and a tail. 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 in the fertilisation of ovum. The middle piece possesses numerous mitochondria, which produce energy for the movement of tail.