plant responses Flashcards
what are some different types of abiotic stress
day length temp lack of water/ excess high wind change in salinity
which abiotic factors have effect on amount of photosynthesis
temperature and daylight hours
what causes leaf loss?
when amount of glucose needed for respiration or maintianing leaves and forming chemicals from chlorophyll to protect from freezing exceeds amount of glucose from photosynthesis.
trees in deciduous woodland with leaves still on more at risk of falling over by winter gales.
what is photoperiodism
sensitive to lack of light
-responses effected by photoperiodism are breaking of dormancy to seed buds so they open up; flowering of plants; and tuber formation
how does daylight effect light sensitive pigments
effects phyochrome (Pr and Pfr) which absorb different types of light depending on light level
falling light levels cause a decrease in which plant hormone? and increase in which other
auxins (leaves respond by producing more ethene)
as well as this causes abscission and dormancy
which area of leaf stalk is sensitive to ethene when light levels drop
abscission zone - which is made from two layers of cells
ethene switches genes in these cells to produce enzymes which digest and weaken walls in the outer layer called the separation layer
what causes a leaf to fall in the absission zone
just read through this you’ll never learn it all
-abscission zone made up of cells sensitive to ethene
-ethene switches off these genes causing the production of enzymes which digest and weaken the cell walls in the outer layer of the abscission zone.
-vascular bundles (like phloem) are sealed off and a fatty deposit forms a protective scar in the separation area when the leaf falls
»>this protects from pathogens
cells deep in separation zone respond to hormones by retaining water and swelling which puts more strain on the outer layer
further abiotic factors (low temps and strong autumn winds finish process causing strain to the leaf and it falls leaving a waterproof scar behind
what happens if cells freeze
their membranes are disrupted and they die
how do plants prevent death by freezing
- cytoplasm of plant cells and sap in the vacuoles contains solutes which lower the freezing point
- some plants produce anti freeze from sugars and amino acids to prevent cytoplasm freeing/ protect cells if they do freeze
> > > different genes switched on/off in response to temps/reduction in day length. sustained warm weather reverses these changes
how do plants use stomatal control to cool the plant
and what is the hormone controlling this
- water evaporates from leaf cells in transpiration/ closure to preserve water
- ABA controls opening and closing and is released by stomatal leaf cells.
how can roots show early warning signs of water stress through levels of ABA
when soil water levels fall and transpiration under threat plant roots produce ABA which is transported to the leaf where it binds to receptors on the plasma membrane of guard cells
what does ABA do
activates change is ionic concentration of the guard cells so reduces tungor pressure so guard cells close and transpiration decreases
what does ABA stand for
absisic acid
which physical defenses protect plants from herbivores
throns, barbs, spikes, fibrous/inedible tissue and hairy leaves w/ stings
name 3 chemical defences of plants
tannins eg) tea and red wine
alkaloids eg) caffeine cocaine
Terpenoids eg)citronella is a bug repellant
what are tannins
phenol group with a bitter taste taking up half the dry weight in leaves.
toxic to insects as they bind to the digestive enzymes produced in their saliva and activate them
what are alkaloids
bitter tasting nitrogenous compound found in many plants affecting the metabolism of animals that take them in. (drug)
caffeine is toxic to insects and fungi and caffeine from coffee spreads into soil preventing germination of other plants
what are Terpenoids
large group of compounds produced by plants which often toxic to insects/ fungi
they produce neurotoxins which interfere with the nervous system
citronella is a natural insect repellant
what are pheromones
chemical made by an organism which affects the social behaviour of members of the same species
»>maple trees when attacked by insects release pheromones which are absorbed by other leaves on branches to make them produce callose to protect them. this also effects other trees nearby
> > > although plants are social and dont rely much on these, but they do allow communication
also in situations a plant can tell if another plant is under water stress by the roots
what are VOC responses
Volatile Organic Compounds which act like pheromones. released into air when a plant attacked by an insect which can cause genes to switch off in the insect as it goes into their saliva
these can deter the pest laying eggs or/
attract a predator of the pest such as wasps to lay eggs inside caterpillars
they can also make nerby plants produce the same chemicals
in venus fly traps te leaves response to touch almost like a muscle possibly due to an electrochemical change in the cells causing an action potential to be reached causing active movement of K+ in. water follows the K+ by osmosis so turgor pressure in upper cells increases.
what are tropisms
plant growth response to a stimuli from 1 direction.
»>triggered by chemical messages produced in response to a particular stimulus.
these movements occur in direct response to environmental stimuli and the direction is where the stimulus comes from
why are germinating seeds used/young seedlings when scientists are researching tropisms
- easy to work with and manipulate as they grow quickly
- changes tend to affect the whole organism
- seedlings of monocotyledonous plants that have shoots in a single spike like wheat (aka a coleoptile) are easier to manipulate than dicotyledonous shoots
what is phototropism a result of
result of auxin movement across a shoot/root as it is exposed to light that is stronger on one side than the other.
»>if plant in normal gravity w/ light all around it will generally grow upwards even in low light
what happens to shoot if plant exposed to light brighter on one side than the other
plant will grow towards light and roots will grow away if exposed allowing max photosynthesis
what are the effects of removing the tip of a shoot and placing a gelatine block and then replacing tip
plant can still move towards light and gelatin allows chemicals to pass through it but not electrical messages. the bending occurs due to the chemical passing from tip.
how was it proved that auxins cause elongation on the shaded side
if thin impermeable barrier of mica placed on shaded side, it prevents the movement of chemicals down the shaded side so there is no response to unilateral light
showed by Darwin and Boysen Jensons experiment
if mica is placed on the side that is facing the light what is the effect?
mica on illuminated side allows the hormone to pass only down the shaded side where it incraeses growth and bending towards the light.
»>this is due to cell elongation so growth towards light.
name some different ways to investiagate tropsims
different conditions (all round unilateral)
grow with different light filters
cover tips with foil/ remove tips , auxin in agar jelly blocks on one side
why can a plant grow rapidly towards the light
which hormone causes this
sometimes grow more rapidly as plant grow rapidly up to find light.
Gibberellins are responsible for extreme elongation of internodes when plant is in the dark
»>when plant exposed to light growth slows as energy used to synthesise leaves and strengthen stems and gibberellin levels fall
how can gardeners use dark conditions to their advantage
forces the speed up of growth eg)rhubarb
(Etiolation) etiolated plants are thin and pale as little chlorophyll is produced due to lack of light
what is geotropism
in normal conditions plants always receive unilateral gravitational stimulus.
roots are positively geotrophic
shoots are negatively geotrophic
how can people investigate geotropism
-clinostat rotating drum
»>rotates 4 turns an hour so stimulus of gravity equal on all sides to stop the accumulation of auxins on one side so they grow straight.
petri dishes in wall of lab and rotate at 90 degree intervals as seedlings grow
what is etoilation
growth in the absence of light and the elongation of stems to try and find light
long internodes and fewer leaves
weakening of cell walls
chlorosis-yellowing of plants due to lack of chlorophyll
which hormone inhibits leaf abscission
auxins
what do cytokinins do
promote cell division
also used to prevent aging of fruit and lettuce
used in micropropagation to control tissue development
what do gibberellins do
- promote seed germination and stem growth causing stem elongation
- trigger metabolism of food stores in germination
- stimulate pollen tube growth in fertilisation
- affect growth of internodes (leaves to stem)
- delay ripening
- in beer speed up malting process
what does abscisic acid do
ABA- inhibits seed germination and growth and
-causes stomatal closure when plant is stressed.
and other protective responses eg antifreeze
what does ethene do
promotes fruit ripening
promotes leaf fall/abscission
how are seedless fruit produced
Gibberellins main
When sprayed on flowers/fruit, any of the plant hormones GIBBERELLINS, auxin and cytokinin could stimulate the development of parthenocarpic fruit. That is termed artificial parthenocarpy.
what does rooting powder do
if cutting taken from plant, rooting powder containing auxins will produce healthy roots quickly.
»>increases successful propagation
micropropagation on a large scale now is good as they create mass of new cells and more cell differentiation.
how do selective weedkillers work
auxins
majority of weeds are broad leaf plants. therefore weedkillers only affect these broad leaf plants
it accelerates its normal shoot growth so the stem can’t support it and it eventually dies.
how is fruit ripening controlled
ethene/ ethylene gas can speed up ripening
kept in cool conditions to inhibit ripening during transportation
how is a seed germinated
involves which hormone
-when seed absorbs water, embryo activated and gibberellins produced.
»»This stimulates the production of enzymes which break down food stores found in the seeds cotyledons in dicot seeds and endosperm in monocot seeds
embryo produces ATP to build and break out of seed coat.
what might gibberellins be causing when seed is germinating in terms of genes
could be causing genes to be switched on/off which code for amylases and proteases (digestive enzymes)
how might ABA affect seed germination
antagonist to gibberellins and interferes with the action of gibberellins
relative levels of each hormone determines when seed will germinate
what do auxins do
control cell elongation prevent leaf fall maintain apical dominance involved in tropisms help w/ ripening stimulate release of ethene
why is it hard to measure changes in plant hormone concentrations
they work at low concentrations
and also because they work in multiple interactions between chemical control systems, it makes it hard to isolate the role of each
what experimental evidence is there to show gibberellins control seed germination
- mutant varieties of seeds which lack the gene to make gibberellins so they don’t germinate
- if gibberellin biosynthesis inhibitors are applied to seeds they dont germinate as they cannot make the gibberellins needed for them to break seed dormancy.
how can commercial plant growers use gibberellins
they can make seeds germinate in conditions they other wise would not
how do auxins move around plant
move up and down stem in transport tissue
they are found in root/shoot tips and meristems
what evidence shows that auxins control apical dominance
- auxins affect the plasticity of the cell wall. The presence of auxins means the cell wall stretches more easily.
- auxins produced in peristem cells and diffuse away from tips of roots and shoots
- when they bind to a specific receptor on the plant cell membrane they drop to pH 5 to keep optimum elasticity/flexible and a vacuole is created
- when the cells mature the auxin is destroyed and pH levels rise again.
> > > this means cell walls become more rigid in shape and size and no longer expand or grow
how do gibberellins effect the amount of amylase produced
they increase the amylase synthesis
»>as amylase is produced by amino acids and storage proteins in the seed embryo when it becomes germinated.
amylase then is used to break down starch to maltose to be used for growth.
how do auxins affect the growth of lateral shoots
supresses lateral shoots
maintains apical dominance
why might there be more lateral shoot growth lower down the plant even if auxins are present
lower concentration of auxin lower down so lateral shoot growth much stronger so branches/stems grow out further
if the apical shoot removed, the auxin producing cells are removed - what happens as a result of this
what if auxins applied arteficially
no auxins produced
lateral shoots free from dominace of apical shoot and grow faster
if auxins reapplied then apical dominance reasserted and lateral shoot growth is supressed.
how does auxin concentration affect root growth
low concentration of auxins = more root growth up to a given concentration
»>higher concentration inhibits root growth but high enough that roots still grow away from sunlight
what kind of amount of gibberellins are produced by a plant with short stems
low conc. gibberellins
how can dwarf varieties of plants be better (plants with low gibberellins)
plant stems much shorter means less waste
+less vulnerable to damage by weather and harvesting
how can effects of different concentrations of hormones be carried out?
serial dillution as they have different affects on growth at different concentration
spread of data should be measured/displayed in standard deviation
apply different concentrations to root tips or cut ends of stem
> > > could also grow hydrophonically (in nutrient not soil)
what is a synergism
different hormones working together, complementing each other and giving greater response than their own
what is antagonism in hormones
substances have opposite effects eg) one promotes growth the other inhibits.
how is fruit ripening controlled
levels of ethene
peak levels of ethene production linked to triggering series of chemical reactions and more respiration
(so more CO2 produced)
describe trends of non-climatic fruit and ethene production
low levels of ethene production
eg)oranges strawberries and melons dont ripen much after picked
which fruits highly affected by ethene production
climatic fruits such as bananas and tomatoes.
»>eg) ripe banana placed in bag of green banans will make them ripen faster even if temps the same than if no ripe banana present as it stimulates ripening of green ones.
how is ethene used to control perfect ripening for sale
harvested fruit is cooled and picked before ripe and transported.
when ready for sale they are sprayed with ethene gas in controlled conditions so batch is ripe at same rate.
»>good as increases time they are good to be sold
why don’t selective weedkillers kill our crop
most crops are monocot plants such as wheat and rice but most weeds are dicot.
»>dicots absorb weedkiller and it disrupts their metabolism.
good as it:
decreases competition
cheap and simple to produce
low toxicity to mammals
