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- Growth Regulators
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- Chemical that controls the growth of plants
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- Cause/stimulate growth
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- Auxins or IAA
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- Produced in the apical meristems
- Found in mostly shoot tips but sometimes root tips
- Developing seeds
- Young leaves
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- Auxins are transported down through the plant in the phloem, where they can have an effect
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- Cause stem elongation
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- By causing cell elongation
- Contributes to :
- Phototropism
- Geotropism
- Fruit Formation
- Involved in Apical Dominance (prevents side branching)
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- To slow or stop growth
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- Ethene (Ethylene) gas
- Abscisic acid
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- Most parts of the plant
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- Causes the ripening of fruit
- Causes leaf fall
- Produced when plants are stressed and wounded
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- The plant stress hormone
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- Causes the stomata to close in times of drought
- Its presence maintains dormancy in seeds which inhibits germination
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- Photosynthesis
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- Ensure enzyme controlled reactions can be carried out
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- 20-30 degrees Celcius
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- To ensure plants flower at the right time of year
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- Ensures that shoot tips grow up to absorb sunlight
- Ensures root tips grow down to absorb water and dissolved minerals
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- The growth response of a plant to a stimulus
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- Growth response of a plant to gravity
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- Roots grow towards gravity
- As they grow towards the stimulus they are positively geotropic
- Shoots grow away from gravity so they are negatively geotropic
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- Growth response of a plant to chemicals
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- Pollen tube grows down in response to chemicals produced by the ovary
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- Growth response of a plant to water
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- Roots grow towards the water which makes them positively hydrotropic
- Shoots grow away from the water which makes them negatively hydrotropic
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- Growth response of a plant to touch
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- Ivy climbing up a wall/house
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- Growth response of a plant to light
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- Stem grows towards the light
- Stems grow towards the stimulus so they are positively phototrophic
- Roots grow away from the stimulus so they are negatively phototrophic
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- IAA is produced in the apical meristem
- IAA moves down both sides equally through diffusion
- Cells in the stem elongate
- This causes stem to grow taller and upright (towards the light)
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- IAA is produced in the apical meristem
- IAA diffuses down the shaded side of the stem
- Because of this the cells elongate faster on the shaded side than the non-shaded side
- As a result the stem bends and grows towards the light
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- Very low concentrations of IAA stimulate root growth
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- Higher levels of IAA stimulate shoot growth but inhibit root growth
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- At very high levels of IAA shoot growth and root growth are inhibited
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- Tissue culture - micropropagation
- Ethene - ripening of fruit
- Rooting Powders - dip cuttings into it, and it promotes growth of roots
- Auxins used to produce seedless fruits
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- Harsh conditions
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- Drought
- Extremely high temperature
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- Discourage or prevent animals from biting the plant
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- Act as a physical barrier
- Prevents the entry of pathogens
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- Prevents excess water loss
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- Inject toxins into animals that brush against them
- This acts as a deterrent to predators
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- Stomata has guard cells that close in times of drought and high temperature
- This is to conserve water loss (low evaporation)
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- Surround enzymes when temperatures get too high
- This stops the enzyme from losing its globular shape and prevents denaturation
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- It is a chemicals produced when a plant is infected by a pathogen
- They can be antibacterial or anti fungal