2.1.11Reproduction and Inheritance

Amniotic Fluid — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 2 Revision Notes & Topical Questions

5 min read 6 parts Lesson 12 of 28

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Part 1 of 4Where the fluid is found

The amniotic sac

The amniotic sac As the embryo develops in the uterus, it becomes surrounded by a bag of thin membrane called the amniotic sac, also known as the amnion.

Amniotic fluid

Amniotic fluid The sac is filled with a watery liquid called amniotic fluid.
- The fetus floats in this fluid for the whole of the pregnancy, from embryo to birth.

Where it sits in the womb

Where it sits in the womb The fluid lies inside the uterus, between the fetus and the muscular uterus wall,
- while the placenta attaches to the lining at one point.

Amniotic fluid

Cushioning

Cushioning Liquids are hard to compress, so the fluid spreads out a knock or pressure over a large area.
- It absorbs bumps when the mother moves, falls or is jolted.

Support

Support The fetus is buoyed up in the fluid, which reduces the effect of gravity on its soft, growing body.

Stable conditions

Stable conditions The fluid helps keep temperature around the fetus steady, giving a constant environment for growth.

Freedom to move

Freedom to move The fluid gives space for the fetus to move its limbs, which helps muscles and bones develop.

Structure	Main job
Amniotic sac	Holds the fluid around the fetus
Amniotic fluid	Protects the fetus from mechanical shock
Placenta	Exchanges gases, nutrients and wastes between mother and fetus
Umbilical cord	Carries fetal blood to and from the placenta
Uterus wall	Muscular tissue that holds the fetus and pushes it out during birth

1Fetus fully developed

Fetus fully developed Near the end of pregnancy the fetus is ready to be born.

2Sac breaks

Sac breaks The amniotic sac breaks and the fluid is released from the vagina.
- This is often called the waters breaking.

3Contractions

Contractions The uterus muscles contract to push the baby out through the cervix and vagina.

Term	Meaning
Amniotic fluid	The liquid surrounding the fetus in the uterus.
Amniotic sac	The membrane that contains the amniotic fluid.
Fetus	The developing baby after the main organs have formed.
Uterus	The organ in which the fetus develops.
Cushioning	Absorbing a knock so the force reaching the fetus is reduced.

Saying that amniotic fluid supplies food and oxygen. That is the job of the placenta and umbilical cord.

Mixing up the amniotic sac (the bag) with the amniotic fluid (the liquid inside).

Giving a vague answer such as 'it protects the baby'. Say it cushions the fetus from bumps when the mother moves.

Placing the fetus inside the placenta; the fetus is inside the sac, connected to the placenta by the cord.

Last updated: 20 October 2026