Human reproductionIB MYP Biology: Revision notes
Section 1
The male reproductive system
The testes make sperm and the hormone testosterone. Sperm travel along the sperm duct, are mixed with fluid from the prostate gland and other glands to make semen, and leave the body through the urethra in the penis.
A sperm cell is adapted for its job: a tail to swim, mitochondria for energy, an acrosome with enzymes to digest the egg's membrane, and a nucleus carrying genetic information.
Section 2
The female reproductive system
The ovaries store egg cells and make the hormones oestrogen and progesterone. About once a month an egg is released and enters the oviduct, where cilia and muscle move it towards the uterus. The uterus is a muscular bag with a soft lining where a baby can develop. The cervix is a ring of muscle at its base, and the vagina is where sperm are deposited during sexual intercourse.
Fertilisation happens in the oviduct. The uterus is where the embryo implants and grows.
Section 3
Fertilisation, implantation and gestation
Fertilisation is when the nucleus of a sperm fuses with the nucleus of an egg to form a zygote. The zygote divides again and again by mitosis to form a ball of cells, the embryo, which travels to the uterus and sinks into its lining. This is implantation.
Gestation is the time from fertilisation to birth, about 40 weeks in humans. The growing baby is called a fetus from about week 8 and floats in amniotic fluid, which cushions it against knocks.
Section 4
The placenta
The placenta grows into the uterus wall and is joined to the fetus by the umbilical cord. Its large surface area and thin barrier let oxygen and nutrients pass from the mother's blood to the fetus, and carbon dioxide and urea pass the other way. The two blood supplies do not mix.
Harmful substances such as nicotine, carbon monoxide, alcohol and some viruses can also cross the placenta, so pregnant women are advised not to smoke or drink alcohol.
The mother's and the fetus's blood do not mix. Substances move across a thin barrier by diffusion.
Section 5
Puberty and sex hormones
Puberty is the stage when the body becomes able to reproduce, usually between about 10 and 16. It is caused by sex hormones carried in the blood.
- Boys: testes make testosterone. Effects: voice breaks, hair on the face and body, muscle growth, sperm production starts.
- Girls: ovaries make oestrogen. Effects: breasts develop, hips widen, hair grows, periods and egg release start.
These changes are called secondary sexual characteristics.
Section 6
The menstrual cycle (simple level)
The menstrual cycle lasts about 28 days.
- Days 1 to 5: the lining of the uterus breaks down and leaves through the vagina (menstruation or a period).
- Days 5 to 14: the lining repairs and thickens.
- About day 14: an egg is released from an ovary (ovulation).
- Days 14 to 28: the lining stays thick, ready for an embryo. If no embryo implants, the lining breaks down and the cycle begins again.
If an egg is fertilised and implants, the lining is kept and the periods stop during pregnancy.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Human reproduction
- A health educator in Nairobi is running a workshop for Year 9 students on how the human reproductive systems work. She uses the terms testes, sperm duct, ovary, oviduct and uterus.Outline two ways in which a sperm cell is adapted for its function.2 marks
- At an antenatal class in Seoul, a midwife explains how a pregnancy develops over about nine months, from fertilisation through to birth. She pays particular attention to the placenta and to what a pregnant woman should avoid.Explain why a pregnant woman is advised not to smoke or drink alcohol.2 marks
- A school nurse in Lagos gives a talk to Year 8 students about puberty and the menstrual cycle. She explains that sex hormones, carried in the blood, cause the changes of puberty, and that a typical menstrual cycle lasts about 28 days, with day 1 being the first day of bleeding.State the name of the main sex hormone in boys and describe two changes it causes at puberty.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).