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
- 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
- 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
- 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.
- 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!