sexual reproduction plants

• types of gametogenesis?


  • megasporogenesis
  • microsporogenesis
• megasporogenesis? (female)


  • megasporocyte divides by meiosis forming 4 haploid megaspores
  • 3 megaspores degenerate and 1 enlarges - forming embryo sac
  • haploid nucleus in sac divides by mitosis forming 8 haploid nuclei
  • 1 is female gamete
  • 2 are polar nuclei
• microsporogenesis?


  • microsporocyte divides by meiosis forming 4 haploid microspores
  • haploid microspores in each microspore divides by mitosis
  • forming 2 haploid nuclei - 1 pollen grain and 1 generative
  • these remain in pollen grain
• how does pollen tube grow?

  • produces enzyme
  • digest tissue providing nutrients
  • grows down style - towards micropyle
  • forming pathway
  • grows best in isotonic - preventing osmotic damage
• double fertilisation?


  • generative nucleus divides by mitosis forming 2 nuclei which are the male gametes
  • one gamete fuses with 2 polar nuclei forming triploid endosperm nucleus
  • one gamete fuses with female gamete forming diploid zygote
• where does double fertilisation occur?

  occurs in the embryo sac
• pollenation?


  • pollen grain lands on germinates on stigma
  • enzyme digests surrounding tissue - providing nutrients
  • helps pollen tube grow down style
  • generative nucleus divides. by mitosis forming 2 male gametes for double fertilisation
• function of triploid endosperm nucleus?

  provides nutrients for the embryo to grow
• advantage if increased pollen tube growth?

  more likely to reach ovule. therefore fertilisation more likely to occur at faster rate