Plant Responses Flashcards
What is abiotic stress
Non-living environmental factor that could harm a plant
How can plants respond to abiotic stress and herbivory
Produce antifreeze enzymes
Produce tannins
Produce alkaloids
How does Mimosa pudica to being touched
Seismonasty causes leaves to fold
What is a plant tropism
Phototropism
Geotropism
Hydrotropism
Thermotropism
Thigmotropism
How is leaf loss in deciduous plants controlled
As leaf ages, cytokinin, auxin levels lower, ethene level increases
Triggers production of cellulase enzymes, which weaken leaves by breaking down cell walls
Leaves break from branch
List the functions of gibberellins
Stimulates
- germination
- elongation at cell internodes
- fruit growth
- flowering
How is germination stimulated
Seeds absorb water, activating embryo to secrete gibberellins
Gibberellins diffuse to aleurone layer, producing amylase
Amylase diffuses to endosperm layer to hydrolyse starch
Hexose sugars act as respiratory substrate to produce ATP
List the functions of auxins
Involved in trophic responses
Control cell elongation
Suppress lateral buds
Promote root growth
Explain why shoots show positive phototropism
Indoleacetic acid diffuses to shaded side of shoot tip
As IAA diffuses down shaded side, it causes active transport of H+ ions into cell wall
disruption to H-bonds between cellulose molecules & action of growth expansions make the cell more permeable to water
Cells on shaded side elongate faster due to higher turgor pressure
Shoot bends towards light
Explain why roots show positive gravitropism
Gravity causes IAA accumulate on lower side of the root
IAA inhibits elongation of root cells
Cells on the supper side of the root elongate faster, so the root tip bends downwards
How do hormones stimulate stomata to close
Abscisic acid binds to complementary receptors on guard cell membrane, causing Ca2+ ions diffuse from vacuole into cytosol
positive feedback triggers other ion channels to open
Other ions diffuse out of cell
water potential of guard cell becomes more positive
Water diffuses out via osmosis
Guard cells become flaccid so stomata close
What is apical dominance
Phenomenon where during the growth of the shoot, the growth of sides shoots does not take place
maintained by the action of auxin, abscisic acid and cytokinin’s
Explain the experimental evidence that auxins maintain apical dominance
Auxin production in apex maintains high levels of abscisic acid. Inhibits growth if side shoots
When apex is removed
- Auxin levels drop, causing abscisic acid
- Cytokinin’s diffuse evenly to promote bud growth in other parts of plant
Explain the experimental evidence that gibberellins control stem elongation and germination
Stem elongation: Tall plants have higher gibberellin concentration than dwarf plants
germination: Mutant seeds with non-functional gibberellin gene do not germinate unless gibberellin is applied externally
How are auxins and cytokines used commercially
Auxins: Rooting powder, growing seedless fruit, herbicides
Cytokines: Prevent yellowing of lettuce leaves, promotes shoot growth
