Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 709–725 of the course textbook. Image credits are on slide 16.
In late childhood the hypothalamus releases more GnRH, so the pituitary releases more LH and FSH. These make the testes secrete testosterone and the ovaries secrete oestradiol and progesterone, which bring about the changes of puberty.
Both have mitosis, growth, two divisions of meiosis and differentiation. Each primary spermatocyte gives four small sperm, millions a day for life. Each primary oocyte gives one large egg, because the cytoplasm divides unequally and polar bodies break down; meiosis pauses twice and finishes only at fertilization.
In the acrosome reaction, enzymes from the sperm head digest a path through the zona pellucida. Once one sperm fuses with the egg, the cortical reaction releases enzymes that harden the zona pellucida, so no other sperm can enter.
The zygote divides by mitosis as it travels down the oviduct and becomes a hollow blastocyst. About a week after fertilization it implants in the endometrium; its outer layer helps form the placenta and its inner cell mass becomes the embryo.
The embryo and young placenta secrete hCG, which appears in urine. Monoclonal antibodies on the test strip bind hCG and are trapped at the test line, giving a coloured line; a control line shows the test worked.
Placental villi give a large surface area for exchange: oxygen and nutrients pass to the foetus, carbon dioxide and urea to the mother, without the bloods mixing. The placenta lets the foetus stay in the uterus to a later stage of development.
Progesterone keeps the pregnancy going, first from the corpus luteum (kept alive by hCG) and then from the placenta. Near term progesterone falls, oxytocin is released and causes contractions, which cause more oxytocin release: positive feedback until birth.
Early observational studies found less coronary heart disease in women taking HRT. Randomized controlled trials later found a small increase. HRT users tended to have higher socioeconomic status, which itself lowers heart disease risk: the correlation was not cause and effect.
Select a video to play it here. Select it again to close it.
Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
The self-check needs JavaScript to run.
A printable worksheet covering all eight statements, from quick recall to data questions and a longer answer. It has 40 marks and takes about 40 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Published hCG, oestradiol and progesterone values through pregnancy, spreadsheet
Safety: No practical hazards. Handle the topic sensitively.
Carry this out with your teacher's supervision and follow your school's lab rules.
Observational studies suggested that hormone replacement therapy protected the heart. A large randomised trial reported in 2002 challenged this.
Women who chose HRT may have differed in other ways. Consider why the design of a study affects how far we can trust its conclusions.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
© 2026 Akash Parthi Bendran. Please ask before using or sharing any resources from this site: see permission to use.