Plant responses Module 5 Flashcards
3 examples of plants increasing their chances of surviving by responding to changes in their environment?
Sense the direction of light and grow towards it
Can sense gravity, so their roots and shoots grow in the right direction
Climbing plants have a sense of touch so can find things to climb and reach the sunlight
2 examples of plants having chemical defences against herbivory?
Produce alkaloids which are chemicals which produce bitter tastes or poisonous
Produce tannins - Taste bitter, and can bind to proteins in the gut to make them hard to digest
2 exampes of plants releasing pheromones in reponse to herbivory?
Release alarm pheremones, in response to herbivore grazing nearby plants can detect these and start making chemical defences
Some plants are able to roll up to protect themselves in response to being?
Touched
How do some plants respond to extreme cold?
Producing their own anti-freeze, the proteins bind to ice crystals and lower the temperature water freezes at
What is tropism?
The response of a plant to a directional stimulus
Positive tropism = growth towards the stimulus
Negative tropism = growth away from the stimulus
What is phototropism?
The growth of a plant is response to light
Shoots are positively phototropic so grow towards light
Roots are negatively phototropic, so grow away from light
What is geotropism?
Growth a plant is response to gravity
Shoots are negatively geotropic so grow upwards
Roots are positvely geotropic so grow downwards
What’s hydrotropism, thermotropism, and thigmotropism?
Plant growth in response to water
Plant growth in response to temperature
Plant growth in response to touch
In plants where are growth hormones produced?
In the growing regions of the plant eg shoot tips and leaves
What does the growth hormone gibberellin stimulate?
Seed germination
Stem elongation
Side shoot formation
Flowering
What does the growth hormone auxin do generally?
Stimulate growth of shoots via cell elongation
High concentrations inhibit growth in roots
Describe what the important auxin (IAA) does?
It stimulates cell elongation, and is move around the cell via diffusion, active transport and via the phloem for long distances
IAA moves to the more shaded parts of shoots and roots, stimulates cell elongation in cells so causes them to grow towards the light. Inhibts growth in roots, causing them to grow away from the light
Moves to the underside of shoots and roots, causing cell elongation in shoots so makes them grow upwards. Inhibits growth in roots so causes them to grow downwards
What’s the shoot tip at the top of a flowering plant called?
Apical bud
How do auxins cause apical dominance?
Auxin stimulate the growth of the apical bud, and inhibit the growth of side shoots from lateral buds - this is apical dominance
This saves energy and prevents side shoots from competing with the shoot tip for light
So plant will grow taller faster to outcompete other plants for light
What happens if you remove the apical bud?
The side shoots will start growing by cell division and cell elongation
How do gibberelins stimulate seed germination?
Triggering the breakdown of starch into glucose in the seed
The plant embryo in the seed can then use the glucose to respire a release the energy it needs to grow
What chemical inhibits gibberellins and therfore seed germination?
The hormone abscisic acid
Gibberellins and auxins are often synergetic what does this mean?
They work together to have a big effect eg. both make a plant grow very tall
Gibberellins and auxins are sometimes antagonistic what does this mean?
They oppose each others actions, eg gibberlins stimulate side root growth, whilst auxins inhibit side shoot growth
What are deciduous plants?
Plants that lose their leaves in winter, to preserve water as difficult to uptake from soil, and there’s not much sun for photosynthesis anyway
Describe how leave loss is controlled by hormones?
Auxins inhibit leave loss, and are produced by young leaves so as they get older are more likely to fall off
Ethene stimulates leaf loss, and is produced by ageing leaves, as the leaf gets older more ethene is produced, causing layer of cells called the abscission layer to form at the bottom of the leaf stalk.
This separates the leaf from the rest of the plant, the abscission layer expands breaking cell walls, and causes the leaf to fall off
Explain how plant hormones are involved in stomatal closure?
Need to be able to close stomata to reduce water loss
This is done using guard cells found each side of the stomatal pore
When they are filled with water, they are turgid and the pore is forced open, when they lose water they become flaccid and the pore is closed
Absisic acid (ABA) triggers stomatal closure by binding to receptors on the guard cell membranes which causes specific ion channels to open, this allows Ca2+ ions in, this increase then causes K+ ion channels to open so they leave the cell, raising the water potential of the cells, so water then leaves the guard cells via osmosis
So the guard cells become flaccid and the stomata close
Give examples of plant hormones in commercial use?
Ethene to ripen fruit at perfect time
Auxins to kill weeds as makes them produce long stems instead of lots of leaves so can’t get enough water or nutrients and they die
Auxins can be used as rooting powders, so make a cut stem grow roots
How does Ethene make fruit ripen?
Stimulates hormones, that break down cell walls and chlorphyll, and convert starch into sugars
