Which of the following is NOT a function of placenta in mammals?

Analyze the question: We need the one option that is NOT a function of the placenta.

Concept: The placenta is a temporary organ that forms in the uterus during pregnancy. It joins the mother's blood supply to the foetus's (through the umbilical cord) without letting the two bloods mix. Its functions are:

1. Nutrient transfer: Digested food (glucose, amino acids, vitamins, minerals) passes from the mother's blood to the foetus. This is the "absorption of food" in option A.
2. Gaseous exchange: Oxygen diffuses to the foetus, and carbon dioxide diffuses back to the mother.
3. Removal of wastes: Urea and other metabolic wastes from the foetus pass into the mother's blood to be excreted.
4. Hormone secretion: The placenta secretes progesterone, oestrogen and hCG to maintain the pregnancy.
5. Protection: It passes antibodies (passive immunity) and acts as a barrier against many harmful microbes.

Checking each option:

• A. Absorption of food: a placental function.
• B. Gaseous exchange: a placental function.
• C. Removal of wastes: a placental function.
• D. Secretion of hormones: a placental function.
• E. Secretion of enzymes: the placenta does not secrete digestive enzymes. The foetus receives food already digested, so no enzyme secretion is needed.

Answer: E, secretion of enzymes.

Exam tip: Remember the placenta as the foetus's lungs, kidney, gut and hormone gland rolled into one. It supplies ready-digested food, so it needs no enzymes. If an option mentions digestion or enzymes, it is probably the odd one out.