Identify placenta umbilical cord amniotic sac and fluid
Original fetal cutaway: placenta at uterine wall, cord to fetus, amniotic sac boundary and fluid within it. Colours identify structures, not blood measurements.
Section B14.2 · Sexual reproduction in humans
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall cell nuclei, gametes, diffusion, respiration and the difference between a cell and an organ.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What links fetus with placenta?
What you will learn
- Locate the four required fetal support structures
- Distinguish exchange connection enclosure and fluid functions
Original teaching model.
| Feature | Meaning |
|---|---|
| 1 · Placenta | Maternal–fetal exchange |
| 2 · Umbilical cord | Fetal vessels linking fetus and placenta |
| 3 · Amniotic sac | Encloses fetus and fluid |
| 4 · Amniotic fluid | Cushioning and movement |
Locate the four required fetal support structures
The fetal-development cutaway shows a fetus within the uterus, surrounded by amniotic fluid inside an amniotic sac. The placenta is attached to the uterine wall, with the umbilical cord linking it to the fetus. The four numbered labels identify different structures: an exchange organ, a connecting cord, an enclosing membrane and the fluid within that enclosure.
The placenta supports exchange of nutrients, gases and waste between maternal and fetal systems. The umbilical cord contains fetal blood vessels connecting fetus and placenta. It does not connect the fetus directly to the maternal heart or carry a shared stream of mixed maternal and fetal blood. The cord is a transport connection; the placenta is the exchange interface.
Distinguish exchange connection enclosure and fluid functions
The amniotic sac encloses the fetus and amniotic fluid. The fluid cushions the fetus, helping protect it from mechanical shocks while allowing movement. It is not a reservoir of blood, a direct food pipe or the maternal bladder. A line pointing to the sac boundary identifies the membrane, whereas one ending in the enclosed blue space identifies the fluid.
This is an original schematic cutaway, not a scale image or a measurement of pregnancy health. Colours distinguish components for teaching and do not imply actual blood colour or universal placental position. Trace attachment and enclosure relationships to identify the parts on another drawing. A complete answer gives each part’s own role without transferring every exchange function to the surrounding fluid.
Sources for this lesson
Pause and explain
What encloses the fluid around the fetus?
Worked example
A leader line ends in the space around the fetus inside the sac. Identify the substance and role.
Show the worked solution
- Distinguish interior contents from enclosing membrane.
- Name cushioning as the relevant support function.
Answer Amniotic fluid: cushions the fetus against mechanical shocks and allows movement.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Name numbered labels 1 and 2 and give their distinct roles.
Give me a hint
Identify exchange organ and connection.
Compare my reasoning
- Locate placenta at the uterine wall.
- Trace cord between placenta and fetus.
1 placenta: supports maternal–fetal exchange; 2 umbilical cord: connects fetus and placenta through fetal blood vessels.
Look for these in your work
- Identify both parts
- Distinguish exchange from connection
Name numbered labels 3 and 4 and give their functions.
Give me a hint
Separate the enclosing membrane from its contents.
Compare my reasoning
- Locate sac boundary.
- Locate fluid surrounding the fetus.
3 amniotic sac: encloses fetus and amniotic fluid; 4 amniotic fluid: cushions against shocks and allows movement.
Look for these in your work
- Separate membrane and fluid
- Give both functions
Correct “the blue fluid is maternal blood directly feeding the fetus, and the cord attaches to the maternal heart”.
Give me a hint
Use the enclosure and exchange relationships.
Compare my reasoning
- Identify fluid within the sac.
- Trace the cord only between fetus and placenta.
The blue region represents amniotic fluid. The cord joins fetus to placenta and carries fetal blood; maternal–fetal exchange occurs at the placenta, not by direct cord attachment to the maternal heart.
Look for these in your work
- Correct fluid identity
- Correct cord connection
Common mistakes
- The fluid is not maternal blood.
- Cord and placenta have different roles.
What can you explain now?
What encloses the fluid around the fetus?
Compare with the explanation
Amniotic sac
The sac is the enclosing membrane.
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Make it stick
Explain locate the four required fetal support structures and distinguish exchange connection enclosure and fluid functions. Use the diagram key and check your reasoning before opening the solutions.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.