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.
