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.