ZIMSEC O Level · Biology · Form 4
Asexual and sexual reproduction
- Asexual: one parent, offspring identical (clones). Examples: binary fission in bacteria, vegetative propagation by runners, tubers and cuttings (sweet potato vines, sugar cane).
- Sexual: two gametes fuse; offspring show variation.
Flowering plants
Pollination is the transfer of pollen from anther to stigma. Insect-pollinated flowers are large, scented and colourful with nectar; wind-pollinated flowers (maize, grasses) have long feathery stigmas and light, smooth pollen. After fertilisation the ovule becomes the seed and the ovary the fruit. Seeds are dispersed by animals, wind, water or explosion.
Humans
- Male: testes make sperm and testosterone. Female: ovaries release eggs and make oestrogen and progesterone.
- Menstrual cycle: about 28 days; ovulation around day 14.
- Fertilisation in the oviduct; implantation in the uterus; the placenta exchanges oxygen, food and waste with the mother's blood.
- Sexually transmitted infections such as HIV, gonorrhoea and syphilis are prevented by abstinence, faithfulness and condom use. HIV is managed with antiretroviral therapy.
Exam tip: Learn functions of the placenta: exchange of substances, barrier to some pathogens, and making hormones.
Check yourself
- Give one advantage and one disadvantage of asexual reproduction.
- State two features of wind-pollinated flowers.
- Where does fertilisation take place in humans?
Show answers
- Advantage: quick, needs only one parent. Disadvantage: no variation, so all may die from the same disease.
- Any two: feathery stigmas, exposed anthers, light smooth pollen, small dull petals.
- In the oviduct.
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