Fertilisation - Flowering Plants (Edexcel International AS Biology)

• Sexual reproduction in flowering plants requires the transfer of pollen between male and female parts of flowers
• 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 pollen is produced
  • The stigma - part of the female reproductive organ which receives the pollen
  • The ovary - where the female gametes are located
• Flowers usually contain both male and female reproductive parts
• The male reproductive parts produce pollen
• The transferal of pollen from the anther to the stigma is known as pollination

Double fertilisation

• After pollination has occurred, the pollen grain begins to 'grow' or 'germinate' and a pollen tube grows from the pollen grain down the style to the ovary of the plant
• As the pollen tube grows towards the ovary, two haploid male nuclei move down the tube
  • These are known as the pollen tube nucleus and the generative nucleus
• At some point, as it travels down the pollen tube, the generative nucleus divides by mitosis to form a further two haploid male nuclei
  • These are the male gametes
  • The two haploid male nuclei travel down the pollen tube towards the female ovule
• As the pollen tube reaches the ovule, the pollen tube nucleus breaks down and the two haploid male nuclei pass into the ovule so that fertilisation can occur
• In fact, a process known as double fertilisation occurs:
  • One haploid male nucleus fuses with the nucleus of the egg cell to form a diploid zygote
  • The other haploid male nucleus fuses with two polar nuclei present in the ovule to form a triploid endosperm nucleus, which will form the endosperm (the food supply for the embryo plant when it begins to germinate)

The process of double fertilisation in plants, in which one male nucleus fuses with the two polar nuclei to form the triploid endosperm nucleus and the other fuses with the egg cell to form the diploid zygote