Reproduction
This domain covers asexual and sexual reproduction, flower structure and double fertilisation, human reproductive systems, and reproductive health.
Asexual reproduction
One parent, no gametes: binary fission (Amoeba), budding (Hydra, yeast), fragmentation (Spirogyra), regeneration (Planaria), spore formation (Rhizopus), and vegetative propagation (sugarcane, potato, Bryophyllum leaf buds). It is fast and produces genetically identical offspring.
Flowering plants
The stamen (anther and filament) is male; the carpel (stigma, style and ovary) is female. Pollination transfers pollen to the stigma; after germination the pollen tube carries two male gametes into the embryo sac. In double fertilisation one gamete fuses with the egg to give the diploid zygote, and the other fuses with the two polar nuclei to give triploid endosperm. The ovule becomes the seed and the ovary the fruit.
Humans
Testes produce sperm and testosterone; ovaries produce ova, oestrogen and progesterone. Fertilisation occurs in the fallopian tube; the zygote divides, implants in the uterus and is nourished by the placenta, which also removes wastes. Gestation is about nine months. Puberty is triggered by hormones, and the menstrual cycle releases one ovum roughly every 28 days.
Worked example
A flower receives pollen from another flower of the same species. The pollen tube delivers two male gametes. One fuses with the egg giving the diploid zygote; the other fuses with two polar nuclei giving triploid endosperm, which stores food for the seed. Two fusions in one embryo sac is double fertilisation.
Traps
Pollination is not fertilisation; the fruit develops from the ovary, not the ovule; the placenta is not the umbilical cord.