Reproduction
Domain 6 covers sexual reproduction in flowering plants and humans and reproductive health. Expect questions on flower structure, gametogenesis, double fertilisation, the menstrual cycle, contraception and STDs.
Core rules
- Anther has microspore mother cells that undergo meiosis to form microspores, then pollen grains. Ovule has megaspore mother cell forming the embryo sac.
- A mature embryo sac has eight nuclei and seven cells: egg, two synergids, three antipodals and a central cell with two polar nuclei.
- Double fertilisation: one male gamete fuses with egg (syngamy) to form zygote; the other fuses with polar nuclei to form triploid endosperm.
- Human spermatogenesis produces four sperm from one spermatogonium; oogenesis produces one ovum and polar bodies. LH surge triggers ovulation.
- Reproductive health includes contraception, prevention of STDs and treatment of infertility.
Worked example
Explain the ploidy of endosperm in an angiosperm. The central cell has two haploid polar nuclei (n + n). One haploid male gamete fuses with them, giving 3n endosperm. The zygote is 2n because egg (n) plus sperm (n). This is why endosperm is triploid while embryo is diploid.
Traps
- Saying endosperm is diploid; it is usually triploid.
- Confusing synergids with antipodals; synergids guide the pollen tube.
- Claiming ovulation is caused by FSH surge; the LH surge triggers it.
- Treating placenta as maternal tissue only; it is formed from both fetal chorion and maternal endometrium.