Science 8th grade
UNIT 5: Reproduction and development 5.3 What happens to the egg cell?
Science 8th grade
UNIT 5: Reproduction and development 5.3 What happens to the egg cell?
After the egg cell is fertilised
The diagram shows what happens to an egg cell, if it meets a sperm cell in the oviduct.
The moment at which the zygote is formed is called conception. It is the start of a new life.
It takes several days for the zygote to become an embryo, and to travel into the uterus. When the embryo has sunk into the wall of the uterus, the woman is pregnant.
It takes about nine months for the tiny embryo to develop into a foetus and then a baby. You can read about this in the next topic.
Questions
1) Name the part of the reproductive system in which fertilisation happens.
2) What is an embryo?
3) Where does the embryo develop into a foctus, and then a baby?
If the egg cell is not fertilised
Most egg cells are not fertilised. They just carry on travelling along the oviduct and eventually dic.
We have seen that, on average, one egg cell is released from an ovary each month. The uterus has to get ready just in case the egg cell is fertilised. The lining of the uterus becomes thick and spongy, ready to receive the embryo.
If the egg cell is not fertilised, this thick lining is not needed. It breaks down, and is lost through the vagina. In an adult woman, this takes about five days and happens about once a month.
The loss of the uterus lining through the vagina is called menstruation, or a period.
The monthly pattern of the thickening and loss of the uterus lining is called the menstrual cycle.
Questions
4) Why does the uterus lining start to grow thick and spongy, as an egg cell develops in an ovary?
5) What happens to the uterus lining if the egg cell is not fertilised?
6) How often does an egg cell leave an ovary in an adult woman?
7) How often does menstruation happen, in an adult woman?