sunflower 5109215 640 Sexual reproduction in plants

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

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

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

Sepals are often green and smaller than the petals. Their job is to protect the flower when it is in the bud.

Pollination

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.

Insect pollination

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.

Wind pollination

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

Wind Pollinated flower

Diagram of insect pollinated flower

Insect pollinated flower

Diagrams of pollen grains highly magnified

Pollen grains

Fertilisation

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

After fertilisation the petals, sepals, carpels and stamens shrivel and fall off. The ovary becomes the fruit and ovules become the seeds.