How do Organisms Reproduce
What the exam tests
How do Organisms Reproduce tests asexual and sexual reproduction, flower structure, pollination and fertilisation, the human reproductive system, puberty, menstruation and contraception. Expect diagram-based and difference-type questions.
Core rules
- Asexual reproduction produces genetically identical offspring. Modes include binary fission (Amoeba), budding (yeast), fragmentation (Spirogyra), regeneration (Planaria), spore formation (Rhizopus) and vegetative propagation (sugarcane, rose).
- Sexual reproduction involves gametes and produces variation. In flowers, the stamen has anther and filament; the carpel has stigma, style and ovary.
- Pollination is transfer of pollen to the stigma; fertilisation is fusion of male and female gametes. Double fertilisation is a feature of flowering plants.
- The human male system includes testes, vas deferens, seminal vesicles, prostate and penis. Testes make sperm and testosterone.
- The human female system includes ovaries, fallopian tubes, uterus, cervix and vagina. Ovaries make eggs, oestrogen and progesterone.
- Menstruation is the shedding of the uterine lining when fertilisation does not occur.
- Contraception may be barrier, hormonal, surgical or intrauterine. STDs include gonorrhoea, syphilis and HIV/AIDS.
Worked example
A gardener wants many rose plants identical to a prize plant. Should he use seeds or vegetative propagation? Seeds involve meiosis and fertilisation, so the offspring vary. Vegetative propagation, such as stem cuttings or grafting, uses mitosis and produces clones. Therefore cuttings or grafting give identical plants, while seeds do not.
Traps that cost marks
- Confusing pollination with fertilisation; they are separate steps.
- Saying binary fission occurs in yeast; yeast buds.
- Writing that the placenta mixes maternal and fetal blood; it allows exchange without mixing.
- Forgetting that the father determines the sex of the child.