Fertilisation & Germination


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Fertilisation & Germination

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