Sexual reproduction in plants

• Stamen


  The male part of the plant consisting of a long filament with anthers at the end which are involved in the production of male gametes in the form of pollen grains
• Carpel


  The female part of the plant which is the site of ovule development
• Pollination


  The process in which pollen grains produced by anthers are transferred to female reproductive organs of a plant in the form of stigma
• Insect pollinated plants


  • Need to attract insects, therefore they have bright coloured petals, a sweet smell and contain nectar
• Wind pollinated plants


  • Have a large amount of light and dry pollen as wind-carried pollen doesn't always reach the plant, as opposed to insect pollinated plants
  • The anthers are located outside the flower and are loose for ease of pollination
  • The stigma is more flexible as it needs to catch drifting pollen
• Self-pollination


  A type of pollination where the pollen from the anthers of a plant is transferred to the stigma of a flower of the same plant
• Cross-pollination


  The pollen from anthers of one plant is transferred to a stigma of a flower of another plant
• Self-fertilised plants display a lesser degree of genetic variation, which can be advantageous in stable environments as the plants which are well suited to that particular environment pass their alleles on
• Double fertilisation


  1. Pollen grain adheres to the stigma and germinates to produce a pollen tube

  2. The pollen tube grows down the style, secreting a digestive enzyme

  3. The pollen tube grows through the micropyle into the embryo sac

  4. The generative cell of the pollen divides to produce two sperm cells which enter the embryo sac

  5. One of the male gametes fuses with the female nucleus to form a zygote

  6. The other male gamete fuses with two polar nuclei to form an endosperm nucleus
• Seed germination


  1. The food store needs to be mobilised

  2. Requires a suitable temperature, good water and oxygen supply

  3. Insoluble food reserves need to be broken down with enzymes

  4. The seed takes up a large amount of water leading to swelling and enzyme activation

  5. Swelling leads to seed coat rupture enabling further development of radicle and plumule
• Plant growth regulators


  Examples include auxins which promote cell elongation, gibberellins which promote seed germination and stem growth, abscisic acid which inhibits seed germination and causes closing of stomata, and ethane which promotes ripening of fruit
• Commercial uses of gibberellins

  • Delay senescence in citrus fruits
  • Elongation of apples in combination with cytokinins
  • Elongation of grape stalks
  • In brewing of beer for production of malt
  • Increase the yield of sugar cane
  • Speed up seed formation in young conifer trees
  • Prevent lodging