The shape of the lesson
By the end of the lesson, learners can
- Supporting the fetus: In the fetus tab the front of the uterus is see-through.
- Exchange at the placenta: Extended.
- Placenta: exchange between mother's and fetus's blood; attached to the uterus wall.
- Umbilical cord: fetus's blood vessels to and from the placenta.
- Amniotic sac and fluid: enclose, support and protect the fetus.
- Extended: O2, glucose, amino acids to the fetus; CO2, urea to the mother; some pathogens and toxins cross too.
One picture every idea returns to
The placenta is attached to the wall of the uterus and the umbilical cord joins it to the fetus; the amniotic sac encloses the fetus in amniotic fluid, which protects it. Extended: in the placenta the blood of the mother and the blood of the fetus come very close but do not mix; dissolved nutrients and oxygen diffuse to the fetus and carbon dioxide and urea diffuse to the mother. Some pathogens and toxins can also cross the placenta and affect the fetus.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Fed, protected, connected.. For about nine months a developing fetus lives in the uterus with no lungs in use and no food of its own. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Supporting the fetus | In the fetus tab the front of the uterus is see-through. Project tab 4 of the lab (The developing fetus) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Exchange at the placenta | Extended. Project tab 5 of the lab (Exchange at the placenta) and let a student drive it while the class predicts. | Connect-Extend-Challenge |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 17 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Exchange at the placenta, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Connect-Extend-Challenge
After the new idea, each student writes three lines: how it connects to what they knew, how it extends their thinking, and what still challenges them. Pairs compare, then the challenges become the plenary.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| The umbilical cord carries the fetus's blood, not the mother's. | The mother's blood stays in her own vessels in the placenta. |
| Do not write that the mother's blood flows into the fetus. | Substances diffuse across the placenta; the two bloods never mix. |
Pregnancy and the placenta: worksheet
6 questions, 17 marks. Written in the style of the papers; no past paper question is reproduced.
State the function of each of: (a) placenta, (b) umbilical cord, (c) amniotic sac, (d) amniotic fluid.
Extended. Describe how the placenta and umbilical cord supply the fetus with what it needs and remove its waste.
Extended. Suggest two features of the placenta that make exchange efficient.
Extended. Name one toxin and one pathogen that can cross the placenta and affect the fetus.
Explain why the blood of the mother and the blood of the fetus must not mix.
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.
Answer key and marking notes
- (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.
- 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.
- 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).
- Toxin: nicotine (from smoking) or alcohol or some drugs.
- Pathogen: rubella virus or HIV (or Zika virus).
- 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).
- 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.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which structure joins the fetus to the placenta?
- Aumbilical cord
- Bamniotic sac
- Ccervix
- Doviduct
What is the main function of the amniotic fluid?
- ATo support the fetus and protect it from bumps
- BTo carry oxygen to the fetus
- CTo remove urea from the fetus
- DTo attach the fetus to the uterus wall
Which describes the amniotic sac?
- AA membrane enclosing the fetus and the amniotic fluid
- BAn organ where the bloods of mother and fetus mix
- CA tube carrying blood from the fetus to the placenta
- DA ring of muscle at the base of the uterus
During which stage is the developing baby first called a fetus rather than an embryo?
- AFrom about eight weeks of development
- BFrom the moment of fertilisation
- CFrom implantation, about a week after fertilisation
- DOnly from birth onwards
Where is the placenta attached?
- ATo the wall of the uterus
- BTo the wall of the oviduct
- CTo the outside of the ovary
- DTo the cervix
Extended: a sample of blood from the umbilical vein has a higher oxygen concentration than a sample from the umbilical artery. What explains this?
- AOxygen diffused into the fetal blood at the placenta
- BThe fetus's lungs added oxygen to the blood
- CMother's blood flowed into the umbilical vein
- DThe umbilical artery carries blood to the placenta from the mother
Extended: which substance diffuses from the fetus's blood into the mother's blood at the placenta?
- Aurea
- Bglucose
- Camino acids
- Doxygen
Extended: a pregnant woman catches rubella. Why may the fetus be harmed?
- AThe rubella virus can cross the placenta
- BThe mother's blood mixes with the fetal blood
- CThe amniotic fluid carries the virus to the mother
- DAntibodies cannot reach the placenta
Quiz key
The umbilical cord links the fetus to the placenta. The amniotic sac surrounds the fetus, the cervix is at the base of the uterus and the oviduct carries the egg.
Amniotic fluid supports the fetus and absorbs shocks. Oxygen arrives and urea leaves through the placenta and umbilical cord; the placenta is attached to the uterus wall.
The amniotic sac is the membrane around the fetus and fluid. The bloods never mix; the blood vessels are in the umbilical cord; the ring of muscle is the cervix.
From about eight weeks the embryo is called a fetus. At fertilisation it is a zygote, at implantation it is an embryo (a ball of cells), and after birth it is a baby.
The placenta develops where the embryo implanted, in the wall of the uterus. The oviduct, ovary and cervix are not sites of implantation.
Fetal blood picks up oxygen by diffusion from the mother's blood across the placenta and returns to the fetus in the umbilical vein. Fetal lungs are not used before birth; the two bloods never mix; the umbilical artery carries fetal blood from the fetus, not the mother's blood.
Urea is an excretory product made by the fetus and removed by the mother's kidneys. Glucose, amino acids and oxygen move the other way, from mother to fetus.
Some pathogens, including the rubella virus, can cross the placenta and affect the developing fetus. The bloods do not mix; the amniotic fluid does not carry the virus to the mother; the problem is the virus crossing, not antibodies.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.