1. Plant Hormones

2. Plant sensitivity Can you explain what is happening.
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3. Plant sensitivity
Can you explain what is happening.
The animation shows the growth of a young shoot towards the light.
Auxins are produced in the shady side of the tip.
The auxins diffuse down the shoot and cause cells behind the tip to elongate.
There is greater growth on the shady side of the young shoot.
The shoot grows towards the light - this is known as PHOTOTROPISM.

5. Auxins are a class of plant growth substance (often called phytohormone or plant hormone).
Auxins play an essential role in coordination of many growth and behavioral processes in the plant life cycle.

6. As auxins contribute to organ shaping, they are also fundamentally required for proper development of the plant itself.
Without hormonal regulation and organization, plants would be merely proliferating heaps of similar cells.

7. An important principle of plant organization based upon auxin distribution is apical dominance, which means that the auxin produced by the apical bud (or growing tip) diffuses downwards and inhibits the development of ulterior lateral bud growth, which would otherwise compete with the apical tip for light and nutrients.
Removing the apical tip and its suppressive hormone allows the lower dormant lateral buds to develop, and the buds between the leaf stalk and stem produce new shoots which compete to become the lead growth. This behavior is used in pruning by horticulturists.

8. Experiment Predict what will happen in each of these experiments.
Click on each shoot to show its growth response.
Normal young shoot
Tip removed from shoot
Tip covered with a foil cap
Tip removed and replaced with an agar block containing auxin
Tip removed and replaced on one side with a small agar block containing auxin

9. Phototropism experiments with coleoptiles

13. Applications of plant hormones
Can you explain the use of hormones in each diagram.
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14. Applications of plant hormones
Can you explain the use of hormones in each diagram.
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Fresh fruits are shipped around the world.
Plant hormones are used to slow the ripening of the fruit, so they are just ripe as they reach the supermarket.

15. Applications of plant hormones
Can you explain the use of hormones in each diagram.
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Powder

16. Applications of plant hormones
Can you explain the use of hormones in each diagram.
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When a gardener takes cuttings from a plant, the base of each cutting is first dipped into a rooting compound to stimulate the growth of roots.
Many rooting compounds contain auxin.
Powder

17. Applications of plant hormones
Can you explain the use of hormones in each diagram.
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18. Applications of plant hormones
Can you explain the use of hormones in each diagram.
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Auxins can be sprayed onto flowers so that the fruits develop without pollination or fertilisation.
These fruits are seedless.

19. Applications of plant hormones
Can you explain the use of hormones in each diagram.
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20. Applications of plant hormones
Can you explain the use of hormones in each diagram.
Click to reveal the answer.
Auxins can be used as herbicides.
Weeds have broader leaves than the grass on a lawn. The weeds will take up more auxin than the grass when the lawn is sprayed.
The weeds will grow too quickly and die.

21. True or false? Which of the following statements is true?
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Gardeners prune to create bushier plants.
This is because pruning causes plants to create...
1. more auxin and this enables side shoots to grow
2. less auxin and this enables side shoots to grow
3. more auxin and this inhibits side shoots from growing
4. less auxin and this inhibits side shoots from growing

22. True or false? Which of the following statements is true?
Click to reveal the answer.
Gardeners prune to create bushier plants.
This is because pruning causes plants to create...
1. more auxin and this enables side shoots to grow
2. less auxin and this enables side shoots to grow 
3. more auxin and this inhibits side shoots from growing
4. less auxin and this inhibits side shoots from growing

23. True or false? Which of the following statements is true?
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Young roots always grow downwards.
This is because roots are...
1. positively phototropic
2. negatively hydrotropic
3. positively geotropic

24. True or false? Which of the following statements is true?
Click to reveal the answer.
Young roots always grow downwards.
This is because roots are...
1. positively phototropic
2. negatively hydrotropic
3. positively geotropic 

25. Plant Hormones
The End