5.1.5 plant responses Flashcards
What are abiotic factors?
Components in an ecosystem that are non-living.
What are some abiotic stresses that plants respond to?
Stomatal closure due to drought.
High temperatures lead to a thicker layer of wax on leaf.
High wind speeds lead to thickened lignin in the vascular tissue.
Rapid growth, spines and thorns in response to predation.
Growth to create shade, production of inhibiting chemicals due to competition.
Arrested growth or dormancy due to water shortage or low temperatures.
Extra nutrient storage due to favourable conditions.
How do plants respond to the threat of herbivores?
They produce chemicals in defence.
What do tannins from plants do?
Toxic to microorganisms
What do alkaloids from plants do?
Derived from amino acids. Very bitter taste. Can affect metabolism of animals, sometimes poisoning them. Caffeine is toxic to fungi and insects, nicotine is produced in the roots of tobacco plants.
What do terpenoids from plants do?
Often form essential oils that act as toxins to insects and fungi, eg citronella.
What do pheromones from plants do?
Released by one individual and can affect the behaviour or physiology of another. Eg Acacia trees release ethene when grazed which causes neighbouring plants to release more tannins.
What are volatile organic compounds?
VOCs act like pheromones.
They diffuse through the air in and around the plant.
They are made for example when a plant is under attack from an insect/pest.
The chemicals may attract a predatory animal to come and consume the original insect or pest.
The VOCs act as a pheromone, causing neighbouring plants to produce the VOC before they are attacked.
What are examples of environmental cues that plants grow due to?
Light (phototropism)
Gravity (geotropism)
Touch (thigmotropism)
Chemicals (chemotropism)
What is the difference between a positive and negative tropic response?
If a plant grows towards the stimulus then it’s a positive response.
If it grows away from it then it’s a negative response.
What do plants use instead of a nervous system to respond to the environment?
They use growth factors/hormones.
These are found in all plant tissues.
What is the role of gibberellins?
Germination of seeds.
Gibberellins stimulate the production of amylase which breaks down starch, releasing glucose for increased respiration.
Causes stem elongation.
What is the role of ethene?
(Sometimes called ethylene) promotes fruit ripening and leaf abscisison.
What is the role of Abscisic Acid (AA)?
It inhibits seed germination and growth causes stomatal closure when the plant is stressed by low water availability.
What is synergism and antagonism in plant hormones?
Synergism is when one hormone increases the effect of another.
Antagonism is where one plant hormone reduces the effect of another plant hormone.
What is the role of plant hormones in seed germination?
Seed coat absorbs water, and embryo is activated and begins to produce gibberellins.
Evidence suggests that gibberellins switch on genes which code for the enzymes that break down food stores inside seeds (amylases and proteases).
Food stores are used to produce ATP for building materials to allow the embryo to grow and break through the seed coat.
Evidence that ABA, another plant hormone, acts as an antagonist to gibberellins - therefore it is the relative levels of each hormone that decides when a seed will germinate.
What is the role of plant hormones in stomatal control?
Cooling of the plant is occurs when stomata open to allow water vapour to be released, carrying heat with it. They also close when water needs to be conserved.
These processes are largely under control of the ABA hormone.
The leaf cells appear to release ABA when under abiotic stress, causing stomatal closure.
ABA is transported to the leaves where it binds to receptors on the plasma membrane of the stomatal guard cells. ABA activates changes in the ionic concentration of the guard cells, reducing water potential and therefore turgor of plant cells. A reduction in turgor causes guard cells to close.
How do plants prevent freezing?
If cells freeze, their membranes are disrupted and they die.
The cytoplasm and sap contain solutes which lower the freezing point.
Different genes appear to be activated and suppressed in response to temperatures which control these activities.
What is the part of the stem that breaks away when the leaf is shed called?
The abscission zone.
What usually inhibits leaf abscission?
Auxins
What is the abscission zone made up of?
Abscission layer and a protective layer.
What happens to auxin and ethene production when the leaf ages?
Auxin production is reduced, this causes an increase in ethene production and makes the cells in the abscission zone more sensitive to ethene.
What does ethene do in leaf abscission?
Ethene increases the production of cellulase (an enzyme that digests cellulose). This digests the cell walls in the abscission zone causing the leaf to fall.
