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Summary Responding to the environment - Plants Grade 12 R50,00
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Summary Responding to the environment - Plants Grade 12
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summary of the Gr12 plants responding to the environment that explains auxins and its functions as well as the trophisms and much more

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  • September 20, 2018
  • 4
  • 2018/2019
  • Summary

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Responding to the Environment-
Plants
Auxins
 Most important group of plant hormones
 Indoleacetc acid (IAA)  most common naturally occurring auxin
 Constantly made by cells in the tp of a shoot (apical bud) small amounts also produced in root tp
 Defuse downwards towards root
 Concentraton highest at the tp and lowest at the root


Functions of Auxins
1.. Auxins promote growth

 Promote both mitosis and cell elongaton
 Further stem tssues are from shoot tp more sensitie they become to auxin concentraton
 If concentraton of auxins are to high cell elongaton will be stopped
 Root elongaton requires less auxins than stems – higher concentratons will inhibit cell elongaton in
roots

2.. Auxins cause apical dominance

 High concentraton of auxins near the apical bud inhibits the growth of the higher lateral buds
 Lower down the plant the auxin concentraton becomes less so lower lateral buds can produce shoots
which grow into lateral branches
 This giies plants a pyramidal shape
 If apical bud is remoied, lateral buds will grow as they are no longer inhibited by auxins and a bushier
plant will deielop

3.. Auxins play a part in trophic moiements

 Brought about by auxins causing cell elongaton on only one side of the stem and root
 Results in uneien growth


Tropisms
 Growth moiements of part of a plant in response to an eniironmental stmulus
 Moiement is dependent on the directon of the stmulus and it results from diferental growth


Phototropism
 Growth response to a light stmulus

Why do shoots respond to light ?
 Auxins = light sensitie hormones
 Moie away from the light source
 Light comes from one directon, auxins from the growing tp moies away from the light source
 Increased concentraton makes these cells elongate more than those on the bright side, so the shoot
bends towards the light
 Shoots/Stems are therefore positiely phototropic
 Roots are negatiely phototropic

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