Express diagrammatically the different phases of spermatogenesis.

The various phases of spermatogenesis are as follows: Multiplication phase - The spermatogonia divide mitotically to produce more number of spermatogonia. Growth phase - The spermatogonia which is also called the primary spermatocyte, simply grows in this phase to divide. Maturation phase - Meiosis-I takes place, in which the maturation of primary spermatocyte (diploid) into the secondary oocyte (haploid) occurs. Meiosis II results in spermatid formation. Spermiogenesis - It is the formation of mature and motile sperms from spermatids.

Write differences between Parturition and Lactation.

Feature Parturition Lactation Meaning This process involves childbirth. This process involves the release of milk from the mammary glands of the mother. Hormone It is initiated by the hormone oxytocin. This process is stimulated by the hormone prolactin.

Why sperms contain mitochondria?

Sperms are the male gamete of human beings. These are microscopic structures that consist of a head, neck, middle piece and tail. There are numerous mitochondria are present in the middle piece of the sperm. It is the site of cellular respiration and energy production. The sperm has to swim inside the female body to fertilize the egg. Hence, it needs a lot of energy. These mitochondria provide energy for the movement of sperms.

Describe the formation of the placenta during the pregnancy.

The implantation of the blastocyst initiates the development of the placenta within the mother's uterus. After the zygote has undergone cleavage and blastulation in humans, the 32-64 celled blastocyst formed with an inner cell mass and the outer trophoblast cells. These trophoblast cells form the placenta while the inner cell mass forms the foetus with other foetal membranes. The placenta is fully formed by 18-20 weeks; however, it continues to grow all through the pregnancy.