(a)(i) What is placentation? (ii) Name two organs associated with the human placenta. (b) State five functions of the human placenta. (c) Write short notes ...

(a)(i) Placentation

Placentation is the formation and manner of attachment of the placenta, the organ that develops in the wall of the uterus and connects the developing foetus (through the umbilical cord) to the mother, allowing exchange of materials between the foetal and maternal blood during pregnancy. (In botany, placentation refers to the arrangement of ovules on the placenta within the ovary.)

(a)(ii) Two organs associated with the human placenta

The uterus (its wall, to which the placenta is attached) and the umbilical cord (which links the placenta to the foetus).

(b) Five functions of the human placenta

• It allows oxygen to pass from the mother's blood to the foetus and carbon dioxide to pass from the foetus to the mother for removal.
• It allows soluble food materials (glucose, amino acids, mineral salts, vitamins) to pass from mother to foetus for nourishment.
• It allows the excretory waste (such as urea) of the foetus to pass into the mother's blood for removal.
• It secretes hormones (such as progesterone and oestrogen) that maintain the pregnancy.
• It acts as a barrier, preventing the mixing of the maternal and foetal blood and keeping out many harmful microorganisms, while allowing some antibodies through to give the foetus immunity.

(c) Short notes

• (i) Viviparity - A mode of reproduction in which the developing young is retained and nourished inside the mother's body (through a placenta) and is born alive, as in most mammals.
• (ii) Territoriality - The behaviour by which an animal establishes, marks out and defends a particular area (its territory) against others, especially members of the same species, for feeding, breeding or shelter.
• (iii) Seasonal migration - The regular, periodic movement of animals from one region to another and back, in response to seasonal changes in the environment, usually in search of food, favourable climate or breeding grounds (for example the migration of birds).