Reproduction and Development
Reproduction and Development tests gametogenesis, hormonal cycles, fertilisation, cleavage, gastrulation and placenta. Expect sequence and timing questions.
Core rules
- Spermatogenesis begins at puberty; oogenesis begins before birth, pauses at prophase I and completes meiosis II only after sperm entry.
- Menstrual cycle: FSH stimulates follicle growth; estrogen rises; LH surge triggers ovulation around day 14; corpus luteum secretes progesterone.
- Fertilisation: acrosome enzymes penetrate the zona pellucida; cortical reaction blocks polyspermy; zygote forms.
- Cleavage gives morula, then blastocyst; implantation occurs in endometrium; gastrulation forms three germ layers.
- Placenta exchanges materials and secretes hCG, hPL, progesterone and estrogen.
Worked example
On about day 14, a spike in LH triggers ovulation. Explain what follows.
Reasoning: the ruptured follicle becomes corpus luteum and secretes progesterone, which thickens the endometrium. If fertilisation occurs, hCG from the trophoblast maintains the corpus luteum. If not, the corpus luteum regresses and menstruation begins. Answer: luteal phase followed by either pregnancy maintenance or menstruation.
Traps that cost marks
- Oocyte completes meiosis II only after sperm entry.
- hCG maintains corpus luteum; it is not the main endometrial hormone.
- Progesterone maintains endometrium.
- Acrosome enzymes, not cortical granules, penetrate the egg coat.
- Cleavage does not increase total mass.