ZIMSEC O Level · Combined Science · Form 3, Form 4
Reproduction in flowering plants
- The stamen (anther and filament) makes pollen, the male gamete.
- The carpel (stigma, style and ovary) contains ovules, the female gametes.
- Pollination moves pollen from anther to stigma, by insects or wind. Fertilisation happens when the male and female nuclei join. The ovule becomes a seed and the ovary becomes a fruit.
- Seeds need water, oxygen and a suitable temperature to germinate.
Human reproduction
- At puberty, hormones cause body changes in boys and girls.
- Fertilisation happens in the oviduct when a sperm joins an egg. The embryo implants in the uterus and develops, receiving food and oxygen through the placenta.
Health and disease
- Diseases caused by pathogens: malaria (a protozoan spread by the female Anopheles mosquito), cholera (bacteria in contaminated water), HIV (a virus spread by body fluids).
- Prevention: clean water and good sanitation, mosquito nets and removing stagnant water, vaccination, and avoiding sharing needles and unprotected sex.
- Drug and substance abuse damages the brain, liver and lungs and leads to addiction.
Exam tip: For disease questions, give the cause, how it spreads and how to prevent it – each usually earns a mark.
Check yourself
- Distinguish between pollination and fertilisation.
- Name the organism that spreads malaria.
- State two ways of preventing cholera.
Show answers
- Pollination is the transfer of pollen to the stigma; fertilisation is the joining of the male and female nuclei.
- The female Anopheles mosquito.
- Any two: boil or treat drinking water, use toilets, wash hands, cover and heat food properly.
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