5.6 Plant responses Flashcards
Why do plants respond to stimuli?
In order to survive.
What is abiotic stress?
Anything that’s potentially harmful to a plant that’s natural but not living
eg drought.
What is herbivory?
When plants are being eaten by animals.
What do plants do to limit herbivory?
•Produce chemicals like alkaloids and tannins to make them taste bitter and deter animals.
•Release pheromes (chemical signallers) to get other plants nearby to respond.
•Nastic movements -Fold up in response to touch. (eg mimosa pudica)
What is a tropism? Positive vs negative?
The response of a plant to a directional stimulus.
A positive is growth towards a stimulus.
A negative is growth away from the stimulus.
What is Phototropism? What are shoots and roots like?
The growth of a plant in response to light.
Shoots are positively phototropic and grow towards the light but roots are negatively phototropic and grow away from the light.
What is Geotropism? What are roots and shoots?
Geotropism is the growth of a plant in response to gravity.
Shoots = negatively geotropic as grow up and against gravity
Roots = positively geotropic as grow down and with gravity
What are the other tropisms other than phototropism and geotropism?
Hydrotropism
Thermotropism
Thigmotropism
Practical to investigate phototropism
- Cover shoot tips in foil and some without
ones with should grow straight up
ones without should grow towards light (bend)
What are the two growth hormones?
Gibberellins and Auxins
What is auxin ? What does it do?
- A plant hormone produced in apical meristems of shoots that causes cell elongation behind the tip on the shaded side.
- It inhibits growth of lateral buds (apical dominance)
- Inhibits leaf fall
- High concs inhibit growth in roots
- Cell elongation.
What is IAA and where is it found?
Indoleacetic acid an auxin found in tips of roots and shoots of flowering plants
How do auxins move?
By diffusion and active transport over short distances and phloem over long distances
What happens if tip of shoot is removed?
No auxin will be produced so plant won’t grow any taller
What is apical dominance?
it’s where auxins stimulate growth of the apical bud and inhibit growth of side shoots from lateral buds.
- The apical bud is dominant over the lateral bud
Why is apical dominance a good thing for plants ?
As it allows the plant to grow up and not out so it isn’t bushy. This means that no leaves are shaded so there’s a higher primary productivity.
What are gibberellins? what do they do?
Hormones produced in young leaves and seeds.
Stimulate
•elongation between internodes
•stimulate seed germination
•side shoot formation
•Flowering
What don’t gibberellins do?
Don’t inhibit growth in any way.
What hormone inhibits gibberellins and what does this cause?
abscidic acid and this causes seed germination to be prevented
What is synergistic?
Where the hormones work together
What is an example of plant hormones being synergistic?
Auxins and Gibberellins working together to help plants grown tall
What is antagonistic?
Where the hormones work against each other and oppose each others actions.
What is an example of antagonistic hormones in plants?
Auxins and Gibberellins as auxins inhibit side shoot growth but gibberellins stimulate side shoot growth.
What are the dominant alleles for gibberellins? what do dwarf plants have?
Le is dominant (has GA)
le is recessive (doesn’t have GA)
dwarf plants have le le and are recessive so have no GA
What hormones control leaf abscission?
- Auxins inhibit leaf loss
- Ethene stimulates leaf loss
How does a decrease in auxin production affect leaf loss?
Increases leaf loss when there is less auxin concentrations
What does an increase in ethene levels do and why?
Causes more leaf loss as the production of cellulase that breaks down cell walls in the abscission layer increase. This causes the leaves to fall
What hormone triggers stomatal closure and how?
Abscisic acid (IAA)
As it binds to receptors on guard cell membranes which cause ion channels to open and more calcium ions enter so this lowers the water potential and causes water to enter by osmosis.
What are the commercial uses of ethene and how does this work?
Used to ripen fruits like bananas.
Fruit picked before ripe and exposed to ethene on arrival to prevent damage.
Works because ethene stimulates enzymes that break down cell walls.
How are auxins used commercially?
How does this work?
- As weed killers
- In rooting powder
Weed killers works as auxins cause plants to produce long stems and no leaves which causes them to die
Rooting powder as it allows cuttings to grow roots and be grown into new plant
