How do plants respond to their environment? Plants can’t move or see! Plants respond to stimuli...
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Transcript of How do plants respond to their environment? Plants can’t move or see! Plants respond to stimuli...
How do plants respond to their environment?
Plants can’t move or see!Plants respond to stimuli
Physical factors ?
Chemical factors
Chapter 14 goals:Know the effects of the 5 main groups of plant hormones:
1. Auxins2. Gibberellins3. Cytokinins4. Inhibitors (Abscisic Acid)5. Ethylene
Understand:PhototropismGeotropismThigmotropism
Relationship between photoperiod and flowering
What is Tropism?
Tropism = Directed Growth +ve toward source–ve away from sourceEg. phototropism
Plants use hormones to direct growth in response to stimuli1. Auxins2. Gibberellins3. Cytokinins4. Inhibitors (Abscisic Acid)5. Ethylene
AuxinsProduced continually in the tip of a shoot
(meristem)Cause localised growthAuxin inhibits lateral bud growthLight effects membrane permeability to auxinDiffuses through cell layers (not vascular
tissue)Moves away from light & softens cell walls
Gibberellins Produced in flowers, fruit, seeds, growing
buds and elongating stemsCause wholesale growth
Cytokinins Stimulates cell division and differentiation Cytokinin : Auxin Ratio Cytokinin = stems and leaves develop
Cytokinin = roots develop
Abscisic AcidGrowth inhibitionProduced in cholorolopastsControls:
leaf drop (deciduos plants)ripe fruit drop bud and seed dormancyVernalisation (flowering after cold)
Protects plants against extreme conditions:Salinity, Temperature & Water levelsControl stomata closure
EthyleneReleased by ripening fruitTriggered by auxin and abscisic acidStimulates further ripening
Increases rate of respirationBreak-down of starch into sugar
Phototropism
Growth towards lightLight effects membrane permeability to auxinDiffuses through cell layers (not vascular tissue)Moves away from light & softens cell walls
Geotropism
Growth in response to gravityStems grow against gravityRoots grow with gravityAmyloplasts involved in direction of root
growth
Apical dominance – one main stem Auxin inhibits lateral bud growthAuxin = taller plants without side branchesBushfire, commercial benefit