Sexual reproduction in plants
Flowers contain the reproductive organs for sexual reproduction in plants.
The stamens are the male organs which produce pollen and the carpels are the female organs which receive the pollen grains. After fertilisation, it is the carpel becomes the fruit and contains the seeds.
Stamens are the male reproductive organs of a flower. Each stamen consists of a filament holding an anther on the end. Anthers release pollen grains when they are ripe.
Carpels are the female reproductive organs of a flower. Each carpel consists of an ovary full of ovules and a style holding out a stigma at one end.
Sepals are often green and smaller than the petals. Their job is to protect the flower when it is in the bud.
Pollination is the transfer of pollen grains from the anther to the stigma. During pollination, the pollen grains are transfered by insects, blown by the wind. They may land on the stigma of the same flower or on the stigma of another flower.
Self-pollination is the transfer of pollen grains from the anther to the stigma of the same flower, or to a different flower of the same plant.
Cross-pollination is the transfer of pollen grains from the anther to the stigma of a flower on a different plant.
Most insect pollinated flowers have nectar which attract insects such as bees. When a bee lands on the flower the pollen grains stick on its coat. The bee then flies to another flower with pollen grains sticking to its body and then deposits the pollen on that flower.
Grasses and cereals are pollinated not by insects but by wind. The flowers are often quite small, green and have no petals. They produce no nectar.
Differences between insect and wind pollinated flowers
|Features||Insect pollinated||Wind pollinated|
|Petals||large, brightly coloured and scented to attract insects into the flower||absent, or small and green|
|Nectar||produced by nectaries to attract insects||absent|
|Anthers||present inside the flower||exposed outside the flower by long filaments in order to expose pollen to the wind|
|Stigmas||small and inside the flower||large, feathery and hanging outside the flower to catch pollen carried by the wind|
|Pollen||smaller amounts of of round and sticky or spiky pollen grains that attach to furry bodies of insects||larger amounts of smooth and light pollen grains, which are easily carried by the wind|
Diagram of wind pollinated flower
Diagram of insect pollinated flower
Diagrams of pollen grains highly magnified
Fertilisation comes after pollination. The pollen grains first germinate microscopic pollen tubes. The pollen tubes grows down the style and into the ovary, allowing the pollen grain to travel down the pollen tube to the ovules, the female sex cells.
Fertilisation then occurs. Fertilisation is the fusion of the male sex cells and female sex cells to produce a zygote. The zygote then develops into an embryo.
After fertilisation the petals, sepals, carpels and stamens shrivel and fall off. The ovary becomes the fruit and ovules become the seeds.