5.5 Plant responses Flashcards
Tropisms, auxin, ethene, gibberellins, apical dominance, commercial uses
What is the name for a plant response
tropism
What are the types of tropism?
Geotropism
Hydrotropism
Phototropism
Thigmotropism
Chemotropism
Explain geotropism
Positive - growing down with gravity e.g. Roots
Negative - growing up against gravity e.g. Shoots
Explain hydrotropism
Positive - growing towards water
Negative - growing away from water
Explain phototropism
Positive - growing towards light e.g. Shoots
Negative - growing away from light e.g. Roots
Explain thigmotropism
Positive - growing towards a touch / solid e.g. A creeping plant
Negative - away from solid touch
—> e.g. venus fly trap
Explain chemotropism
Positive - growing towards a chemical
Negative - growing away from a chemical
How does auxin act in plant cells?
- Auxin lowers the pH of the cell by causing H+ ions to accumulate (more acidic conditions)
- This enables enzymes that produce or stretch cellulose to function
- Once there is no auxin, the cells can no longer elongate
Auxin results in cell elongation
What is a nastic movement?
A response which is not related to the direction of the touch stimulus
—> e.g. Mimosa leaves snapping shut
How do plants respond to herbivory?
Produce chemicals:
Alkaloids
Pheromones
What are alkaloids?
Nitrogenous compounds: bitter tasting + can be toxic
–> e.g. caffeine + nicotine ( a neurotoxin)
What are pheromones?
Chemicals released by one plant which affects the behaviour/physiology of another:
—> oxides of ethene switch on genes to produce chemicals that deter insects
What are responses to abiotic stress?
- Plants can respond to drought by shutting their stomata
- producing an antifreeze chemical in their cells, that decreases the formation of ice crystals in cells
What is the function of auxin
Results in cell elongation in response to phototropism
What is the function of ethene
Results in ripening of fruits