Gametes, fertilisation and pregnancy
Introduced| English | Meaning |
|---|---|
| embryo/ˈembrɪəʊ/ | The early developing stage after fertilisation, before it is called a fetus. |
| implants/ˈɪmplænts/ | Embeds into the uterus lining, as an embryo does. |
| placenta/pləˈsentə/ | An organ that enables exchange between the mother's blood and the developing fetus without their blood normally mixing directly. |
From gametes to a baby
- A new human life begins when two tiny cells meet, and then grows protected inside the mother.
- The journey runs from gametes to fertilisation to pregnancy.
Fertilisation to pregnancy
Follow the route from gametes to implantation.
Compared with the egg, the sperm cell is:
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Sperm are small and motile; eggs are large with food.
Sperm and egg
- The sperm is small, has a tail to swim, and carries little food.
- The egg is much larger and contains a food store for the early embryo 胚胎.
The uterus lining thickens, an egg is released at day 14, and a period follows if there is no pregnancy
Put these stages of early development in order.
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Gametes fuse → zygote → embryo → implantation.
The embryo settles into the lining of the uterus in a process called ______.
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Implantation begins pregnancy.
Fertilisation and implantation
- A sperm fuses with the egg → a zygote, which divides to form an embryo.
- The embryo implants 植入 in the lining of the uterus and continues to grow.
The placenta allows the baby to receive:
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Oxygen and nutrients diffuse across; waste passes back.
In the placenta, the mother's and baby's blood flow close but do not mix.
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Substances pass by diffusion across a barrier.
The placenta 胎盘
- The placenta exchanges substances between the mother's blood and the baby's.
- Oxygen and nutrients pass to the baby; carbon dioxide and waste pass back — by diffusion.
The fetus develops in the uterus, joined to the placenta by the umbilical cord
The mother's and baby's blood don't mix. They flow close together in the placenta, but substances pass by diffusion across a barrier. Mixing would be dangerous because their blood types may differ.
You've got it
- the sperm is small with a tail; the egg is large with a food store
- fertilisation → zygote → embryo, which implants in the uterus
- the placenta exchanges oxygen/nutrients and waste by diffusion (blood doesn't mix)