How do Organisms Reproduce
What is tested
This domain tests asexual and sexual reproduction, flower structure, pollination, fertilisation, human reproductive anatomy, menstrual cycle, placenta and contraception. Questions often ask you to distinguish similar terms.
Core rules
- Asexual modes include fission, budding, fragmentation, regeneration, spore formation and vegetative propagation. They produce genetically similar offspring.
- Sexual reproduction involves gametes and produces variation. In flowers, pollen transfers by pollination; fertilisation is fusion of male and female gametes.
- Double fertilisation in flowering plants: one male gamete fuses with the egg to form the zygote; the second fuses with polar nuclei to form endosperm.
- In humans, testes produce sperm and testosterone; ovaries produce eggs and oestrogen. The placenta exchanges materials between mother and foetus.
- Contraception includes barrier methods, hormonal pills, intrauterine devices and surgical methods such as vasectomy and tubectomy.
Worked example
After pollination, a pollen tube grows through the style to the ovule. One male gamete fuses with the egg, giving a diploid zygote. Another male gamete fuses with two polar nuclei, giving triploid endosperm. This is double fertilisation.
Traps
Pollination is transfer of pollen; fertilisation is fusion of gametes. The placenta is not a barrier that blocks all substances. Menstruation is not the same as ovulation. Vegetative propagation is asexual, even though it uses plant parts.