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.

Fertilsation

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.