13) Plant Responses Flashcards
Why do plants need to respond to stimuli?
-Increase survival to changes in the environment
-Survive with response to herbivory (eaten by animals)
-abiotic stress
How do a plants survive to changes in the environment
Grow towards light to maximise photosynthesis.
Roots and shoots grow towards or away from gravity
How to plants survive against herbivory
1) Toxic Chemicals
Alkaloids - bitter taste,smell, poisonous
Tannins - bitter taste , bind to proteins in gut - deter animals from eating plants
2) Pheromones
Signalling chemical , produce a response in other organisms
3) Fold up when being touched
How to plants survive against abiotic stress
abiotic - nonliving
eg, antifreeze proteins
Describe Phototropism response in plants
-Response to light
Shoots are positively phototrophic grow towards the light
Roots are negatively phototrophic and grow away from the light
Descripe Geotrphic response in plants
Response to gravity
Shoots are **negatively geotrophic ** and grow upwards
Roots are Postively geotrophic and grow downwards
Describe how plants responds to growth hormones
Can speed up or slow down growth
Gibberellins - Stimulate seed germination,stem elongation ,side shoot formation , flowering
Auxins - Stimulate growth of shoots by cell elongation
Why is Indoleacetic (IAA) an important auxin
Stimulate cell elongation
moved around to control tropisms - by diffusion and active trasnport
Cause an uneven distribution of IAA auxins to cause uneven growth.
Describe how IAA move in the plant in response to light and gravity .
Phototropism - IAA moves to shaded parts of roots and shoots , cause uneven growth
Geotropism - IAA moves to the underside of shoots and roots , cause uneven growth
What is apical dominance?
How are auxins involved in Apical Dominance
The apical buds is dominant over lateral buds.
Auxins stimulate the growth of apical buds and inhibit growth of lateral buds.
Why is the use of apical dominance important?
Prevents side shoots growing , saves energy from same plant competing for light.
Allow plants to grow tall very fast and reach sunlight
What is proof that auxins control apical dominance?
(observation proof)
Remove apical buds , won’t produce auxins so side shoots will start growing by CD and cell elongation.
Replace tip with source of auxins , side shoots are inhibited.
Auxins become less conc as they move away from the apical buds
At bottom of tall plant , low auxin conc , so side shoots start to grow near bottom
Describe the use of Gibberellins
Produced in young leaves in seeds
stimulate seed germination,stem elongation,side shoot formation ,flowering
Seed germination - Trigger breakdown of starch into glucose , plant embryo use glucose to respire and release energy to grow . Gibberellins are inhibited by abscisic acid.
How are hormones involved in leaf loss
Auxins inhibit leaf loss - less auxins produced as gets older so leaves fall
**Ethene **stimulate leaf loss - Ages leaves , as get older more ethen produces .
Abscission layer develops at bottom of leaf stalk and seperate leaf . Cells expand and break cell walls .
Lose leaves to conserve water during cold weather .
Triggered by shortened day length
How are hormones involved in stomatal closure
-Reduce water loss through transpiration
Abscisic acid (ABA) trigger stomatal closure
Binds to guard cell membranes , ion channels open ,ca ions enter cytosol from vacuole.
Ion channels open other ions leave , raise water potential of cells .
Water leaves leaves and guard cells are flaccid
Cause stomata to close
