Plant Responses Flashcards
How do plants increase their survival chances against herbivores?
Physical defenses: Thorns, stings, spikes
Chemical defenses: Alkaloids - nitrogenous, bitter tasting chemicals - affects metabolism
What are alarm pheromones?
plants release alarm pheromones to warn other plants of herbivores
This stimulates them to synthesise toxic chemicals.
Other pheromones attract predators to eat pests
What does the mimosa pudica do in response to touch?
It folds up its leaves in response to touch
This helps to knock off or scare any insects
How do plants respond to cold temperatures?
Plants synthesise antifreeze proteins that prevent ice crystals from forming
What are tropisms?
Directional growth responses of an organism is response to a stimuli
Plants show phototropism and geotropism
What is phototropism?
a directional response to sunlight
Plant shoots show positive phototropism and grow towards the sun
Roots show negative phototropism and grow away from the sun
What is geotropism
A directional response to gravity
Plant shoots show negative geotropism and grow against the force of gravity
Plant roots show positive geotropism and grow with the force of gravity
What are the 4 main plant hormones?
Gibberellins - stimulate seed germination and flowering
Abscisic acid (ABA) - stimulates stomatal closure and seed dormancy
Auxins - cell elongation in stems and inhibits cell growth in roots
Ethene - stimulates flowering and fruit ripening
What is indoleacetic acid (IAA)?
Type of auxin
Promotes cell elongation in shoots
Inhibits growth of cells in roots
made in tip of roots and shoots
How does auxin work?
Auxin accumulates on the underside of shoots and roots
In shoots, auxin causes cell elongation which causes it to bend upwards against gravity
In roots, auxin inhibits cell growth which causes roots to grow downwards with gravity
What is apical dominance?
The growth of the apical bud at the expense of the side shoots growing
Promoted by auxins
How do auxins promote apical dominance?
Auxins prevent the growth of side shoots to save energy and prevent competition for light between the main shoot and side shoots
Less energy used for side shoots so more used so the plants grows taller and maximise sunlight absorbtion
What happens when the apical bud is removed?
Auxin levels drop which causes side shoots to start growing.
If the tip of shoot is replaced by an agar block containing auxin, the growth of side shoots is inhibited
What are gibberellins?
plant hormones that stimulate seed germination, growth of side shoots, stem elongation and flowering
switch on genes that code for amylase and protease
What is leaf abscission?
Controlled by hormones of deciduous trees in winter
Trees loose leaves in colder temperatures to conserve water during winter when there is less photosynthesis
How does leaf abscission occur?
Auxin inhibits leaf abscission and ethene promotes abscission
Auxin levels drop and ethene rises
when ethene reaches a certain levels, the abscission layer develops at the base of the leaf stalk
The cells in the layer expand in response to ethene and the cell walls break and the leaf breaks off
How do guard cells control the closing and opening of stomata?
When guard cells of full of water they become turgid which pushes the stomatal pore open
When guard cells lose water they turn flaccid and close the stomatal pore
How is the guard cell controlled?
Controlled by the plant hormone abscisic acid (ABA)
ABA binds to receptors on guard cell membrane causing calcium ion channels to open
Influx of calcium ions causes potassium ion channels to open and potassium ions leave the guard cell
Water potential in guard cell increases and water moves out of cell by osmosis. Guard cell becomes flaccid and pores close
What are commercial uses of plant hormones?
Auxins are used in rooting powders
Auxins used in herbicides
Ethene is used to control fruit ripening
