Reproduction
What you must understand
Know the difference between sexual and asexual reproduction. Sexual reproduction involves two parents, gametes and fertilisation, and produces variation. Asexual reproduction involves one parent and produces genetically identical offspring.
Learn the human reproductive systems. Male: testes produce sperm and testosterone; sperm travel through the sperm duct and urethra. Female: ovaries produce eggs and oestrogen; the egg travels along the oviduct to the uterus, where the lining thickens. Know the events of the menstrual cycle and the roles of oestrogen and progesterone.
Understand fertilisation (fusion of gametes in the oviduct), implantation, the placenta (exchange of substances between mother and fetus) and the adaptations of the placenta: large surface area and thin barrier. The umbilical cord carries fetal blood to and from the placenta.
In plants, learn the parts of a flower: sepals, petals, stamens (anther and filament), carpel (stigma, style, ovary). Pollination is the transfer of pollen; fertilisation is the fusion of gametes. Seeds form from the ovule and fruit from the ovary.
Traps examiners set
- Confusing pollination with fertilisation.
- Saying the placenta lets the mother's blood mix with the fetus's blood. They do not mix; substances diffuse across.
- Forgetting that the oviduct is where fertilisation normally happens.
- Mixing up which gamete carries which sex chromosome: the sperm determines sex.
Worked example
A question asks why sexual reproduction is an advantage. Answer: it produces genetic variation in offspring, which increases the chance that some survive changed conditions or disease.
Rule of thumb: pollination is pollen transfer; fertilisation is fusion of nuclei. Keep the two words apart.