Inheritance and Selection Human Reproduction
Lesson Aims • To ensure all students know the structure and function of the human sex organs. • To understand the process of human fertilisation • To be aware of the sequence of events in the development of a human foetus • To understand the structure and function of the placenta.
Human sex organs • Answer all questions on the sheet you are given. • Stick the sheet in your exercise books.
Fertilisation • Ejaculation produces about 5 ml of semen which contains 450 million sperm.
Fertilisation • Although thousands of sperm may reach an egg, only one enters it.
Fertilisation • To be successful the sperm must meet the egg in the Fallopian tube.
Fertilisation • The tail of the sperm remains outside as the head travels through the egg cytoplasm to the nucleus.
Fertilisation • Fertilisation occurs when the sperm nucleus fuses with the egg nucleus to form a zygote. This is the moment of conception.
Diary of human development Week 0 • Egg is fertilised in the fallopian tube.
Diary of human development Week 1 • Embryo becomes attached to the lining of the uterus (womb).
Diary of human development Week 2 • Foetus eyes begin to develop. Its legs and arms are tiny bumps.
Diary of human development Week 6 • Foetus begins to look like a human. Ears, hands and feet begin to grow. Heart begins to beat.
Diary of human development Week 10 • Foetus fingers and toes grow. It can move its arms and legs a little – it can swallow and frown.
Diary of human development Week 14 • It is possible to determine the foetus’s sex.
Diary of human development Week 18 • Foetus has hair, eyebrows. Doctors can hear the heartbeat. Mother begins to feel its kicks.
Diary of human development Week 26 • Foetus opens its eyes.
Diary of human development Week 30 • If born now, the baby could live with special care.
Diary of human development Week 34 • Baby has grown a lot of fat in the last 4 weeks, to keep it warm when it is born.
Diary of human development Week 38 • Baby is born.
The Placenta Stick the diagram of the placenta in your books
The placenta • The zygote divides as it passes to the uterus and becomes and embryo. • The embryo implants in the thick lining of the uterus.
The placenta • Finger like extensions called villi project from the embryo into the lining of the uterus eventually forming the placenta.
The placenta • The embryo develops into a foetus attached to the placenta by the umbilical cord.
The placenta • An artery and a vein run through the umbilical cord and connect the foetus’ blood system to the placenta.
The placenta • The foetus blood system IS NOT DIRECTLY CONNECTED to the blood system of the mother.
The placenta • The exchange of oxygen, food and wastes between the mother and foetus depends on diffusion across the thin wall of the placenta.
The placenta • Harmful substances such as nicotine, alcohol, drugs and virus can also pass across the placenta from the mother to the foetus.
The placenta • The _______ grows from the _______ • The foetus is connected to the placenta by the __________ _________ . • In the cord there is an _______ and a _____ coming from the foetus. • The placenta brings the _______ of the foetus very ________ to the blood of the _______ but the different ___________ do not mix.
The placenta • ___ and ____ pass from the mother’s ______ into the foetus. _____ , ______ and other _______ substances pass from the _____ into the _______ blood. • Harmful substances such as _______, ______, ________ products and _____ can also pass into the foetus through the _________ from the mother.