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IGCSE · Practice questions · Pregnancy and the placenta

Life support in the uterus.

Six original Cambridge-style questions on the structures that support the fetus and (Extended) exchange across the placenta.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Close, but never mixed.

01
Recall
[4 marks]

State the function of each of: (a) placenta, (b) umbilical cord, (c) amniotic sac, (d) amniotic fluid.

  • (a) Placenta: exchange of substances between the mother's blood and the fetus's blood. ✓
  • (b) Umbilical cord: joins the fetus to the placenta; carries the fetus's blood to and from the placenta. ✓
  • (c) Amniotic sac: membrane that encloses the fetus and amniotic fluid. ✓
  • (d) Amniotic fluid: supports and protects the fetus from mechanical shock. ✓
02
Explain
[4 marks]

Extended. Describe how the placenta and umbilical cord supply the fetus with what it needs and remove its waste.

  • Oxygen and dissolved nutrients (glucose, amino acids) diffuse from the mother's blood across the placenta into the fetus's blood. ✓
  • The umbilical vein carries this blood to the fetus. ✓
  • Carbon dioxide and urea are carried from the fetus in the umbilical artery to the placenta. ✓
  • They diffuse across the placenta into the mother's blood, to be excreted by her lungs and kidneys. ✓
03
Explain
[2 marks]

Extended. Suggest two features of the placenta that make exchange efficient.

  • A large surface area (many finger-like villi). ✓
  • A thin barrier between the two bloods, so a short diffusion distance (also: good blood supply on both sides keeps gradients steep). ✓
04
Recall
[2 marks]

Extended. Name one toxin and one pathogen that can cross the placenta and affect the fetus.

  • Toxin: nicotine (from smoking) or alcohol or some drugs. ✓
  • Pathogen: rubella virus or HIV (or Zika virus). ✓
05
Explain
[2 marks]

Explain why the blood of the mother and the blood of the fetus must not mix.

  • The mother's blood pressure is much higher and could damage the fetus's small blood vessels. ✓
  • Keeping them separate stops many pathogens and harmful substances in the mother's blood reaching the fetus (blood groups may also differ). ✓
06
Data
[3 marks]

Extended. Blood samples were taken from the umbilical cord. Sample X had more oxygen and glucose and less urea than sample Y. State which sample came from the umbilical vein and explain your answer.

  • X came from the umbilical vein. ✓
  • The umbilical vein carries blood from the placenta to the fetus. ✓
  • At the placenta this blood has gained oxygen and glucose by diffusion and lost urea to the mother's blood. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.