Date post: | 01-Jan-2016 |
Category: |
Documents |
Upload: | gwenda-mckenzie |
View: | 219 times |
Download: | 0 times |
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