plant responses Flashcards
what are the limitations for plant responses
.the plants are rooted to the ground so they cannot move
.plants do not have a nervous system
how do plants respond to their enviroment
via producing hormones which are transported throughout the plant
what are gibberellins
plant growth regulators which stimulate seed germination
how do gibberellins control plant height
they cause the elongation of plant stems during growth which increases the length of the internodes
why can it be beneficial to have fewer gibberellins
.they have shorter stems which makes it less vulnerable to damage from weather or harvesting
how does gibberellins start the germination process in seeds
.water enters the seed which causes the embryo to synthesise gibberellins
.as a response, amylase and maltose enzymes are synthesised
.amylase hydrolyses starch stored in the endosperm into maltose which can be further broken down into glucose
what is evidence for the role of gibberellins in germination
.when gibberellins are added to seeds that cannot produce gibberellins germination occurs
what are synergistic plant hormones
hormones that work together to give off a bigger response
what are antagonistic plant hormones
hormones that have opposing effects
e.g. one causes growth and the other inhibits growth
what do auxins regulate
.cell expansion and differentiation
.suppression of lateral bud growth(apical dominance)
.directional growth responses(tropisms)
how do high levels of auxins effect plant tissues
.inhibit root growth and promote shoot growth
how do low levels of auxins effect plant tissues
promote root growth and inhibit shoot growth
process of elongation
auxins are synthesised by meristem in shoot tips
.auxins diffuse down shoot away from tip
.auxins bind to receptor sites on cell-surface membranes
.cell walls have low pH
.cells absorb water via osmosis forming vacuoles and increasing internal pressure
.this causes cell walls to expand which results in cell elongation = cell grows
role of IAA (auxin) in apical dominance
.IAA is synthesised at shoot tips and stimulates growth of apical shoot and suppresses the growth of lateral shoots
.removal of apical bud where the IAA is synthesised means that lateral bud can growth leading to a bushier plant
plant abiotic stresses
.day length changes
.excess cold or heat
.lack of water
.high winds
.change in salinity
what is photoperiodism
the sensitivity of plants to levels of light
what is the photoperiodism for deciduous trees
summer = daylight hours are at a maximum and trees are covered in leaf = maximising photo and growth
autumn = lengthening of dark period = leaf fall
winter = daylight hours are at a minimum = trees maintain a period of dormancy
spring = days lengthen and temp rises = trees come out of dormancy
what are phytochromes
.pigment that sense the duration of light and darkness
.Pr and Pfr
how do phytochromes effect plant responses
.breaking dormancy in buds
.initiating tuber formation
.timing the flower phase
what is abscission
when plants loose leaves
how is abscission triggered
.lengthening of dark period during autumn leads to lower photo rates
.energy demands for respiration outweighs glucose availability
.dormancy is needed to avoid winter damage
process of leaf abscission
.decrease in light causes a decrease in auxin levels
.ethene is release by leaves
.ethene switches on genes in cells in the abscission zone at the base of the leaf stalk
.enzymes digest and weaken cell walls in the separation layer
.vascular tissues are sealed off blocking transport to the leaf
.fatty material is deposited in the cells in the inner protective layer of the abscission zone
.cells within the separation layer swell with water, straining weak walls
.environmental factors like winds separate the leaf from the plant
.protective layer that remains forms a scar to prevent the entry of pathogens
what are some plant responses to freezing temperatures
.synthesising compounds e.g. sugars, amino acids and proteins acting as antifreeze
.modulating gene expression to bolster cold resistance
.adjusting sap solute concentration to lower freezing point
the role of ABA in stomatal regulation
.when there is low water, ABA is produced
.the ABA moves from the roots to the leaves and binds on to guard cells
.ABA activates changes in the ionic conc of the guard cell reducing WP
.this makes the stomata close minimising water loss
what are some of the physical defences against herbivores
.thorns, barbs and spikes
.tough, fibrous tissue
.stinging hairs
.densely hairy leaves
what are some of the chemical defences against herbivores
tannins
alkaloids
terpenoids
what do alkaloids do
.alkaloids like cocaine and morphine to affect the metabolism of the animals
alkaloids like caffeine and nicotine are toxic to animals
what do VOCs do
the affect the social behaviour of the other members of the same species or a different species
what is the purpose for having VOCs
.they attract predators
.they repel herbivores
.signalling neighbouring plants
what are tropisms
.they are directional growth responses for plants
what are phototropisms
they maximise the ability of the plant shoots and leaves to absorb light
.positive = shoot grows towards light
.negative = shoot grows away from light
what is geotropism
.helps plants establish its roots and shoots in the optimal orientation
.positive = root grows towards the gravitational pull
.negative = root grows away from gravitational pull
how are phototropism and geotropism regulated
IAA directs plant responses to the phototropism or geotropism
positive phototropism in plant shoots
.IAA is produced in the tip of the shoot and is transported down the shoot
.light stimulates IAA to move from light side of the shoot to the shaded side
.IAA becomes concentrated and stimulates more cell elongation on the shaded side
.shoot bends towards light
negative phototropism/ positive geotropism in plant roots
.IAA is produced in the tip of the shoot and is transported along the root
.any light stimulates IAA to move from the light side to the shaded side
.gravity pulls IAA from the upper side to the lower side of the root
.IAA becomes concentrated and inhibits cell elongation in the lower shaded side of the root
.root bends away from light and downwards towards gravity
what is etiolation
.the rapid upward growth that takes place in plants grown in the dark
.thin and pale due to lack of chlorophyll
gibberellins role in plants that are in the dark
.they cause extreme elongation of the internodes
.this helps seedlings to grow out of soil
what are some commercial uses for plant hormones
.ethene is used to control fruit ripening
.auxins are used in rooting powders and micropropagation
.auxins are also used for weedkillers
