plant hormones Flashcards
what is the advantage of apical dominance to plants
- prevents side shoots from growing which saves energy, and prevents side shoots from the same plant competing with the shoot tip and lower leaves for light.
This allows plants to grow tall very fast
what is the role of the plant hormone auxin
stimulates growth of the apical bud, inhibits growth of side shoots from lateral buds, therefore promotes apical dominance
how does the concentration of auxin differ down the plant
auxin becomes less concentrated further away from the apical bud, therefore side shoots grow at the bottom
what is the role of giberellins (2)
stimulates the stems of plants to grow via stem elongation in the internodal regions.
stimulates seed germination and flowering.
outline how giberellin stimulates seed germination
seed germination is activated by water, radical and pineal cells produce giberellin which activates genes to produce amylose which breaks down starch in the endosperm to glucose, which is used for respiration
explain the 2 terms that can describe how auxins and giberellins work together
they are synergistic - work together to have a large effect, larger than they would have working independantly eg. help plants grow very tall
they are antagonistic - oppose each others actions eg. giberellins stimulates growth of side shoots, auxin inhibits the growth of side shoots.
why is leaf loss in deciduous plants an advantage
losing leaves in winter helps conserve water which may be difficult to absorb from the soil.
reduces energy needed to maintain leaves in the winter, fallen leaves insulate roots, rotten leaves provide minerals in the soil
outline and explain the 2 hormones involved in leaf loss
leaf loss is triggered by shortening day lengths which is detected by receptors called phytochromes.
auxins inhibits leaf loss
ethene stimulates leaf loss, a layer of cells called the abscission layer develops at bottom of leaf stalk. Ethene stimulates the cells in the abscission layer to exapnd and activates genes to produce digestive enzymes which break down the cell wall, causing the leaf to fall off
what plant hormone is involved in stomatal closure
abscisic acid (ABA)
outline how the hormone ABA triggers stomatal closure
- ABA binds to receptors on guard cell membrane
- ion channels open, Ca 2+ ions enter the cytosol from the vacuhole
- increased conc. of Ca2+ ions causes more ion channels to open, which allows ions to leave the guard cell.
- water potential increases
- water leaves the guard cell via osmosis.
- cell becomes flaccid and stomata closes
give an example of how a plant may respond to abiotic stress
carrots produce antifreeze proteins, these bind to ice crystals and lower the temp that water freezes at, preventing more icecrystals from forming.
what are alkaloids, give an example
chemicals with a bitter taste, noxious smell or poisonous characteristics that deter or kill herbivors.
Tobacco plants produce the alkaloid nicotine, which is highly poisonous to insects.
what are tannins
plants produce tannins in response to herbivory, they have a bitter taste, and in some herbivors can bind to proteins in the gut making them hard to digest.
what are pheremones
signalling chemicals - plants can release alarm pheremones in the air in response to herbivore grazing, this causes nearby plants to start maming chemical defences.
give an example of how pheremones deter herbivores
corn plants are eaten by catepillars, they release pheremones which causes parasitic wasps to kill the catepillars