Fertilisation & Germination

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  • 1. Fertilisation in Plants Concluding Plant Reproduction
  • 2. Plant fertilisation
    • When pollen sticks to the stigma it absorbs water and starts to germinate
    • A pollen tube will grow out of the grain and through the style towards the ovary
  • 3. Plant fertilisation
    • The pollen tube nucleus remains close to the tip of the tube.
    • Digestive enzymes are secreted from the tube.
    • The tube is attracted by chemicals given out by the ovary.
  • 4. Plant fertilisation
    • As the tube grows the generative nucleus divides by mitosis to form two haploid male gametes.
  • 5. Plant fertilisation
    • The pollen tube enters the ovule through the micropyle.
    • Once inside the ovule the tube nucleus degenerates and the male gametes enter the embryo sac
  • 6. Plant fertilisation
    • One of the male gametes fuses with the female gamete forming a diploid zygote .
    • In plants a double fertilisation takes place as the other male gamete fuses with the diploid nucleus in the centre of the embryo sac forming a triploid nucleus – called the endosperm nucleus.
  • 7. Outbreeding mechanisms
    • How plants prevent self-fertilisation
  • 8. Protandry
    • Most flowers use this mechanisms, e.g. rose-bay willowherb
    • The stamens ripen before the stigma is receptive to pollen.
    • So pollen is gone by the time stigma is ready.
  • 9. Protogyny
    • More unusual than protandry e.g. the bluebell
    • The stigma ripens before the anthers.
    • By the time the anthers shed their pollen the stigma is no longer receptive to it.
  • 10.  
  • 11. Dioecious Plants
    • With dioecious plants each individual plant bears either male or female flowers, but never both.
  • 12. Dioecious Plants
    • Paw-paw and holly are examples of dioecious plants.
    • Clearly self-pollination is impossible!