Plant Reproduction (HL IB Biology)

Production of Gametes

• In flowering plants, male and female gametes are produced in the anther and ovule (see diagram below for position of these structures), respectively
  • Male gametes are contained within pollen grains, which are released from the anthers
    
    • The anther contains pollen sacs
    • Each pollen sac contains a diploid mothercell which undergoes meiosis to form four haploid pollen grains (the gametes)
    • Mitosis occurs to produce more haploid male gametes
  • Female gametes are made in the ovules
    • A single diploid cell within the ovule undergoes meiosis to produce four haploid egg cells
    • Only one of these cells survives which undergoes mitosis to produce female gametes

Pollination and Fertilisation 

• Pollination is the process of transferring pollen from the anther of one flower to the stigma of another
  • Some flowering plants are hermaphroditic which means they contain both male and female parts 
    • Self pollination can occur in some of these species when pollen is transferred between different flowers on the same plant, or even from anther to stigma within the same flower
  • Cross pollination is the transfer of pollen from one plant to another
    • Flowers make use of a variety of methods, such as shape, colour and scent, to attract pollinators to aid with pollination
  • All pollination methods are forms of sexual reproduction because the gametes are produced by meiosis so there is fusion of gametes to form a diploid nucleus
• After pollination has occurred, a pollen tube grows from the pollen grain down the style to the ovary of the plant
• The male nuclei travel down the pollen tube to the female ovule
  • Two male nuclei travel down the pollen tube to the ovule; one will fuse with an ovule nucleus to form the zygote while the other will go on the form the plant embryo's food store
• Fertilisation occurs when the haploid male and female nuclei fuse and a diploid zygote is formed
  • After fertilisation, the ovule becomes a seed and the ovary develops into the fruit

Fertilisation in flowering plants diagram

The process of fertilisation in a flowering plant to produce an embryo

• The development of flowers occurs in the reproductive stage of the plant life cycle
• Flowers contain all the necessary organs and tissues required for sexual reproduction by pollination
• Key structures of the flower include
  • The anther - where the male gamete, pollen, is found
  • The stigma - part of the female reproductive organ which receives the pollen
  • The ovary - where the female gametes are located

Insect pollinated flower diagram

The structure of an insect pollinated flower

Flower structures and their functions table