A baby grows inside the mother's uterus. There it is protected and fed. The baby cannot eat, breathe or remove its own waste. A grown person can do these th...
Question 1 Report
A baby grows inside the mother's uterus. There it is protected and fed. The baby cannot eat, breathe or remove its own waste. A grown person can do these things. So the mother's blood must do them for the baby. The exchange happens at the placenta. The placenta joins to the baby by the umbilical cord. Here the two bloods come very close. But they do not mix. Useful things and wastes pass between them. A student was asked how the baby gets food and oxygen. The student also looked at how the baby removes its waste.
(a) Name the organ at which substances are exchanged between the mother and the developing baby. [1]
(b) Name the structure that joins the developing baby to this organ. [1]
(c) Name two useful substances that pass from the mother's blood to the baby's blood. [2]
(d) Explain how the developing baby gets rid of the carbon dioxide and urea that it produces. [3]
(e) Explain one reason why it is important that the blood of the mother and the blood of the baby do not mix. [3]
Answer Details
This question tests how the developing baby is fed and how its wastes are removed at the placenta, where the two bloods come close without mixing.
(a) The organ where substances are exchanged between mother and baby is the placenta [1].
(b) The structure joining the baby to the placenta is the umbilical cord [1].
(c) Any two useful substances passing from mother to baby: oxygen; glucose (food/nutrients); water; mineral ions; antibodies [2, 1 each].
(d) The baby removes carbon dioxide and urea by diffusion. These wastes are more concentrated in the baby's blood [1], so they diffuse across the placenta into the mother's blood down the concentration gradient [1]; the mother then removes them from her own body using her lungs (carbon dioxide) and kidneys (urea) [1].
(e) One reason the bloods must not mix, developed for 3 marks: the mother's blood may be at a higher pressure and could damage the baby's delicate vessels [1]; the mother and baby may have different blood groups whose bloods could react (agglutinate) [1]; and keeping them separate means harmful substances or some pathogens in the mother's blood are kept from the baby [1].
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