Fertilisation of plants

• Plants use pollination as the transfer of pollen from the anther to the stigma
• In plants, the male gametes is contained within the pollen grain. The female gamete is embedded deep in the tissue of the ovary.
• The pollen grain lands on the surface of the stigma of the flower during pollination. If the pollen grain and stigma are of the same species, the pollen grains begins to grow or germinate. A pollen tube begins to grow out of the tube cell of the pollen grain through the stigma into the style. The tip of the pollen tube contains hydrolytic enzymes to digest the tissue of the style.
• As the pollen tube grows town towards the ovary, the pollen tube nucleus and the generative nucleus travel down it. The generative nucleus divides by mitosis as it moved down the tube to form two male nuclei. These are the male gametes. The tip of the pollen tube passes through the micropyle of the ovule and fertilisation occurs.
• Flowering plants undergo double fertilisation. One male nucleus fuses with the two polar nuclei to form the endosperm nucleus which is triploid. The endosperm is involved in supplying the embryo plant with food when it begins to germinate. The other male nucleus fuse with the egg cell to form the diploid zygote.
• 1. Pollen grain
  2. stigma
  3. Style
  4. pollen tube
  5. Ovule
  6. ovary
  7. The pollen tube nucleus degenerates after pollen tube enters the ovule

  
• The carpel (female part of the plant) is made up of:

  • ovary
  • stigma
  • style
• The stamen (male part of the flower) is made up of:

  • anther
  • filament
• Macrospore (female sex cell)

  It is made up of 8 nuclei and is called the ovule

  1. antipodals
  2. polar nuclei
  3. synergid
  4. ova (haploid)

  
• Microspore (male sex cell)

  A microspore is pollen, and is made up of two haploid nuclei

  1. Generative nucleus
  2. Pollen tube nucleus

  
• Both the microspore and macrospore divide by meiosis to become the microspore and macrospore
• When the pollen grain lands on the stigma of the plant, it will fertilise the ovule if the pollen is of the same species as the plant. The pollen tube nucleus will penetrate the stigma, using hydrolytic enzymes to break down the stigma tissue.

  The generative nucleus divides by mitosis to make two identical haploid cells (can be called sperm). The pollen tube nucleus dissolves as if reaches the ovule by apoptosis. One of the haploid cells fertilises the egg cell to form the zygote. The other fertilised the two polar nuclei to form the endosperm nucleus
• The endosperm surrounds the embryo to make up the seed. It is a triploid cell(3n) because it is made up of 2 polar nuclei and one male haploid nuclei. The endosperm provides nutrition for the growing embryo.