Sexual reproduction in plants
Section: Biology | Syllabus: Cambridge IGCSE Combined Science (0653)
Structure of an Insect-Pollinated Flower
The parts of an insect-pollinated flower can be identified in diagrams and images, and their functions stated:
- Sepals - protect the flower bud before it opens
- Petals - large and brightly coloured to attract insect pollinators
- Stamen - the male part, made up of:
- Filament - the stalk that holds the anther in position
- Anther - produces pollen grains, which contain the male gametes
- Carpel - the female part, made up of:
- Stigma - a sticky surface that receives pollen during pollination
- Style - connects the stigma to the ovary; the pollen tube grows through it
- Ovary - contains one or more ovules
- Ovule - contains the female gamete
The stamen is the male part of the flower; the carpel is the female part
Wind-Pollinated Flowers
Wind-pollinated flowers have anthers and stigmas that are structurally different from those of insect-pollinated flowers:
- The anthers hang loosely outside the flower on long filaments, so pollen is easily released into the wind
- The stigmas are large, feathery, and hang outside the flower to catch airborne pollen
Exposed anthers and feathery stigmas maximise the chance of catching wind-blown pollen
Pollination
Pollination is the transfer of pollen grains from an anther to a stigma.
Fertilisation in Plants
Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule.
Common Mistakes
- ❌ Confusing pollination with fertilisation
- ✓ pollination is the physical transfer of pollen from anther to stigma; fertilisation is the fusion of the pollen nucleus with a nucleus in the ovule. Pollination must happen first, but it does not guarantee fertilisation will follow
Conditions Required for Seed Germination
Investigations into seed germination show that it depends on three environmental conditions:
- Water - needed to rehydrate the seed and activate enzymes
- Oxygen - needed for aerobic respiration, which releases energy for growth
- A suitable temperature - needed for enzymes to work effectively
Common Mistakes
- ❌ Thinking that light is required for germination
- ✓ light is not a requirement for germination - the seed uses the food store in its cotyledons until the seedling emerges and begins photosynthesising
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