Reproduction in Organisms and Human Reproduction
This domain tests asexual and sexual reproduction, gametogenesis, the menstrual cycle, fertilisation, implantation, pregnancy and parturition.
Core rules
- Asexual reproduction uses mitosis: binary fission in Amoeba, budding in Hydra and yeast, fragmentation in Spirogyra, and vegetative propagation in plants.
- Spermatogenesis begins at puberty and is continuous; oogenesis begins in the fetal ovary and arrests in prophase I until ovulation.
- In a 28-day cycle, FSH stimulates follicle growth, an LH surge triggers ovulation near day 14, and the corpus luteum secretes progesterone.
- Fertilisation normally occurs in the ampulla of the fallopian tube; the blastocyst implants about day 6-7, and hCG maintains the corpus luteum.
Worked example
A woman has a 28-day cycle and ovulates on day 14. Intercourse occurs on day 10. Conception is possible because sperm can survive up to about five days in cervical mucus, while the oocyte is viable for roughly 24 hours. The sperm from day 10 could therefore reach day 14-15, although intercourse on days 12-14 is more likely to conceive. The reasoning uses gamete survival, not a fixed fertile day.
Traps
- Ovulation is not day 14 in every woman or every cycle.
- hCG rescues the corpus luteum; progesterone is the main luteal hormone.
- Spermatogenesis is continuous from puberty, whereas oogenesis has long arrest phases.
- Implantation follows blastocyst formation, not fertilisation directly.