How do Organisms Reproduce?
Reproduction covers asexual modes, sexual reproduction in flowering plants, human reproductive anatomy, puberty and contraception. Diagram labelling and why-questions dominate this domain.
Asexual reproduction
Binary fission (Amoeba), budding (yeast, Hydra), fragmentation (Spirogyra), regeneration (Planaria), spore formation (Rhizopus), vegetative propagation (sugarcane, potato). It is fast and gives genetically identical offspring, a disadvantage in a changing environment.
Flowering plants
Stamen = anther + filament (male); carpel = stigma + style + ovary (female). Pollination transfers pollen to the stigma; fertilisation fuses gametes inside the ovule. Double fertilisation: one male gamete fuses with the egg, the other with two polar nuclei to form endosperm. Ovule becomes seed, ovary becomes fruit.
Humans
Testes make sperm and testosterone; ovaries make eggs and oestrogen; fertilisation occurs in the oviduct; the placenta exchanges nutrients. Puberty is triggered by hormones; the menstrual cycle averages about 28 days with ovulation near day 14. Contraception: barrier, hormonal, IUCD and surgical methods.
Worked example
An Amoeba divides every 30 minutes. In 2 hours there are four divisions, so the number of cells is 2 to the power 4 = 16. Starting from one cell the growth is exponential, which is why binary fission multiplies bacteria so rapidly.
Traps
Treating pollination as fertilisation; placing fertilisation in the uterus when it occurs in the oviduct; confusing the ovary's role with the placenta's.