Plant Responses - Module 5 Flashcards
What are 3 main uses of commercial plant hormones?
- Control of ripening
- Hormone rooting powder and micropropagation
- Hormonal weedkillers
How are plant hormones used to control the ripening of fruit?
Plants will be harvested prior to ripening so they are hard and less likely to be damaged during transport
Once ready to be sold they are exposed to ethene - the hormones that makes them ripe
How are plant hormones used commercially for micropropagation?
Adding auxins to cut shoots promotes the growth of new shoots, thus enhancing the success of propagation of new plants from cuttings
How are plant hormones used commercially in hormonal weedkillers?
As interactions between plant hormones are balanced to prevent growth, the interruption of this balance may disturb the metabolism of the plant and subsequently kill it
What hormones are used in weedkillers and what effect do they have on the plant?
Synthetic dicot auxins, impact the metabolism of a plant and they die
What is a tropism?
Plant growth response to a stimuli from one direction
What is a phototropism?
Plant growth response to light
How do phototropism’s occur?
Occur as a result of the movement of auxins across the shoot or root (if the root is exposed to light) that is stronger on one side than the other
What way will shoots grow in regard to light?
Shoots are positively phototropic and will grow towards light
What way will roots grow in regard to light?
Roots are negatively phototropic and will grow away from the light
What plant hormones controls stomata control?
ABA hormone causing stomata to close
Why do plant hormones control the stomata?
To open the stomata to cool the plant and close the stomata in order to conserve water
What is a specific response of the mimosa pudica?
Plants folding in response to touch
- potassium ion movement and osmotic water movement allow the leaves to curl and unfold scaring herbivores and dislodging insects
What do tannins do as a plant chemical defence?
Tannins are toxic to insects as well as contain a phenol compound which is bitter
What do alkaloids do as a plant defence chemical?
Contain bitter nitrogenous compounds and are toxic to animals acting as poison
What do terpenoids do as a chemical plant defence?
Toxic to insects and fungi
List some physical defences a plant may have to protect itself [4]
- Thorns
- Barbs
- Spikes
- Stings
What is a pheromone? And give an example in plants
A chemical made by an organism affecting the social behaviour or other organisms in the same species
E.g maple trees release pheromones when under attack telling leaves on other branches to deposit callouses as a defence
What are VOC’s in plants?
VOC’s are volatile organic compounds which act in a similar way to pheromones but interact with insects rather than other plants
Where are auxins made?
Auxins are made in the roots, shoots and meristems of a plant
Why do plants grow in the dark more rapidly?
Because they are trying to reach light in order to photosynthesise
What is geotropism?
Plant growth response in regard to gravity?
How do shoots response to gravity?
Shoots are negatively geotropic and will grow upwards
How do roots respond to gravity?
Roots are positively geotropic and will always grow downwards
How do gibberellins affect elongation of plant stems?
Gibberellins affect the length of the internodes - regions between leaves on a stem
How are gibberellins involved in seed germination?
Evidence suggests gibberellins switch on genes that produce amylases and proteases - digestive enzymes required in germination breaking down the food stores in the seed
What are the two pieces of experimental evidence that proves gibberellins are involved in seed germination?
- Scientists breed mutant seeds which lack the gene to make gibberellins - the seeds do not germinate. If gibberellins are then applied externally they will germinate
- If gibberellin inhibitors are applied the seed will not germinate, if taken away the seed will germinate
What are auxins?
Growth stimulant hormones produced in plants
How do auxins affect the main apical shoot of a plant?
Auxins affect the plasticity of the cell wall, meaning it will stretch more easily
They do this by binding to receptors on cell membrane causing pH to drop to the optimum 5, for enzymes to keep cell wall flexible
What effect do high concentrations of auxins have on a plant?
High concentrations of auxin suppress lateral growth of shoots resulting in apical dominance
What is apical dominance?
Apical dominance is the occurrence of auxins preventing lateral shoot grown
What experimental evidence is there to show that auxins have an impact on apical dominance?
If the apical shoot is removed, lateral shoots will grow faster and if auxins are reapplied to apical shoot the growth of lateral shoots will decrease again
What do low concentrations of auxins promote?
Root growth
What is a synergism?
When different plant hormones work together resulting in a greater response than the one provided when the hormone acts alone
What is an antagonism?
When plant hormones have the opposite affect and the balance of the hormones determines the effect on the plant
Which hormones are involved in the falling of leaves on trees?
Auxins and ethene
How do auxins and ethene cause plants to drop their leaves? [5]
- As light levels fall, concentration of auxins fall
- Leaves response to fall in auxin by producing ethene
- Ethene stimulates production of digestive enzymes
- Digestive enzymes weaken cell wall at ABSCISSION ZONE
- Vascular bundles seal, Leaf falls
How does a decrease in temperature affect plants?
If cells freeze membranes are disrupted and the plant will die
How have plants adapted to prevent freezing?
Cytoplasm of plant cells contain solutes that lower the freezing point e.g sugars, amino acids and proteins
