plant responses Flashcards
(62 cards)
outline 3 roles of hormones in plants
- cellular communication
- to respond to external stimuli
- to signal to other plants or species nearby e.g. protecting themselves from pests/insects or producing chemical defences against herbivores
what are the 5 main plant hormones
gibberellins
ethene
auxins
cytokinins
abscisic acid - ABA
where are gibberellins found
plant seeds and apical portions of roots and shoots
what do gibberellins do in plants
when seeds absorb large amounts of water, gibberellin is released to start the process of germination - it stimulates enzymes to break down / metabolise food stores
what are gibberellins used for by humans
gibberellins are used to end seed dormancy, so seeds can be planted all year round
they are also used to control fruit ripening
where is ethene found
leaves, stems and young fruits
what does ethene do in plants
it promotes leaf fall in deciduous trees and causes fruit ripening
what is ethene used for by humans
since it affects plant growth, it can be used alongside gibberellins to prevent spoiling / ripening / overripening of fruit during transport, and then to promote fruit ripening when in stores
where are auxins found
found in shoot apical meristems and roots
what do auxins do in plants
auxins are growth factors, produced in tips of roots and shoots, in shoots they cause the stem to grow upwards while also stopping lateral buds from growing, promoting apical dominance
they also prevent leaf fall
why is apical dominance important in a plant
the higher up a plant grows the more light it has access to
how do changing auxin levels affect other hormones in a plant
if auxin levels / production is low, ethene is stimulated
give an example of a specific auxin
indoleacetic acid - IAA
what happens if the growing tip of a plant is removed
this is where the auxins are found / produced, so this means the source of auxins has also been removed, so apical dominance is no longer promoted - with time the lateral shoots will grow and curl towards the light
what are auxins used for by humans
they are used as selective weed killers - since they are growth hormones, they cause weeds to grow very quickly, meaning they absorb nutrients from soil at a faster rate, and so weed killer is also absorbed much faster
they are also used to promote growth of plant cuttings as they allow the roots to develop quickly so plants can self sustain
where are cytokinins found
they are produced in the roots and transported around the plant from there
what do cytokinins do in a plant
they work alongside auxins to stimulate cell division, and play a role in determining the course of differentiation
where is ABA found
in mature leaves, fruits and root caps
what does ABA do in a plant
it slows and inhibits growth, maintains seed dormancy and is involved in stomatal closure - it can start to accumulate when plants experience stresses, such as changes in temperature, water levels or salinity
outline how ABA could help a plant deal with water stress
low water levels are detected by the plant, causing ABA to accumulate and travel to leaves, where high levels of ABA cause the stomata to close, so less water is lost via transpiration
what is ABA used for by humans
it is used to prevent seed development, such as to produce seedless fruit, which is easier to sell
what are the 6 stages of life in a plant
seed dormancy
germination
growth to maturity
flowering
fruit development
leaf abscission
what hormones are involved in seed dormancy
ABA
what hormones are involved in germination
gibberellins
