Reproduction, growth and development
What this domain tests
The male and female reproductive systems, gamete structure, the menstrual cycle and its hormones, fertilisation, implantation, the placenta and gestation, plus growth curves and puberty. Diagram questions on the reproductive systems and the cycle graph are common.
Core rules
- Sperm: head with acrosome and nucleus, middle piece packed with mitochondria, tail for swimming. The egg is large, with food reserves, and one is usually released per cycle.
- Testes produce sperm and testosterone; the epididymis stores sperm; the vas deferens carries them; the prostate and seminal vesicles add fluid.
- The menstrual cycle averages 28 days. FSH from the pituitary matures a follicle; oestrogen from the follicle thickens the uterine lining and triggers the LH surge; LH causes ovulation around day 14; the corpus luteum secretes progesterone, which maintains the lining. Without fertilisation, progesterone falls and menstruation begins.
- Fertilisation occurs in the oviduct and forms a zygote, which divides by mitosis into a ball of cells that implants in the uterus. The placenta allows exchange of glucose, oxygen and antibodies while keeping fetal and maternal blood separate; the umbilical cord joins fetus to placenta; amniotic fluid protects and supports the fetus. Gestation is about 40 weeks.
- Growth is a permanent increase in size and mass by cell division and enlargement; development includes differentiation. Puberty brings secondary sexual characteristics under sex hormones.
Worked example
A woman has a regular 28-day cycle and ovulated on day 14. She had intercourse on day 11. Could she conceive? Yes. Sperm survive in the female tract for up to about three to five days, so sperm deposited on day 11 could still be viable on day 14 when the egg is released. The egg survives only about 24 hours, so the fertile window is roughly days 10 to 15. Conception does not require intercourse on the exact day of ovulation.
Traps that cost marks
Saying fertilisation happens in the uterus. Treating the placenta as a barrier to everything; alcohol, nicotine and some viruses cross it. Confusing the roles of oestrogen and progesterone. Implying that the umbilical cord carries maternal blood into the fetus, which it does not; the two blood supplies remain separate.