plant responses and plant hormones Flashcards
what are abiotic and biotic stimuli that cause plant response and how
abiotic= light, drought, freezing, wind, high temp= plant can close stomata
biotic= herbivory= phermones and alkaloids = have a bitter taste
what are two types of plant responses
nastic= non-directional responses to an external stimuli
tropism= growth responses to an external stimuli
what is an example of nastic response
rapid response to touch by sensitive plant (mimosa pudica) is an example of thigmonasty= plant closes/ folds up leaves
what is positive and negative tropism
positive= growth towards stimuli
negative= away from stimuli
what are the different types of tropism and explain them
-phototropism= shoots are positively phototropic= grow towards light for photosynthesis
-geotropism= roots are positive, shoots are negative= roots grow towards pull of gravity=anchoring plant and water and mineral uptake
-hydrotropism= overrides geotropism, grows towards water
-thigmotropism= touch= shoots of climbing plant wind around other plants for structures to gain support
chemotropism= chemicals= pollen tubes grow towards chemicals in ovary carrying reproductive cell
where are hormones transported to target cells in plants
transported by diffusion, active transport, or mass flow in phloem sap or xylem vessel
what are similarities and differences between plant and animal hormones
same;
-bind to complementary receptors on membranes of target cells
different:
-some plant hormones amplify effects of other hormones= agonists
-some cancel out effects of other hormones= antagonistic
-plant hormones influence cell division, cell elongation or cell differentiation
what is the effect of the ethene hormones
promotes fruit ripening
what is the effect of gibberellins hormone
promote seed germination and growth of stems
what is the effect of auxins e.g IAA hormones
promote cell elongation, inhibit growth of side shoots/ maintain apical dominance, inhibit leaf abscission(fall), stimulate ethene
-involved in tropism
what is the effect of abscisic acid hormone
inhibits seed germination and growth, causes stomatal closure when plant is stressed by low water availability, stimulate antifreeze production in response to cold
what is the effect of cytokinins hormone
promote cell division, delay leaf ageing, overcome apical dominance, promote cell expansion
explain the mechanism of auxin
-auxin synthesised in meristem cells in tip of plant
-diffuses down away from tip
-binds to receptor sites
-decrease pH in cells and vacuole forms
-low pH/ high H+ causes; hydrogen bonds within cellulose to be disrupted and expansis able to operate as wall looseing enzymes operate at optimum pH
-vacuoles absorb water and get bigger= cell stretched
-auxins destoryed by enzymes, cell wall become rigid= no further elongation possible
what does Darwin and Boysen-jensen’s experience prove about the effect of auxin
- control= auxin in tip moves to shaded side causing cell elongation, shoot bends towards light
2.tip removed= no auxin which is produced in tip= plant grows up - tip covered in opaque cap= cells producing auxin in tip cannot detect light= plant grows up
- tip covered by transparent cap= light detected= auxin diffuses down shaded side= cell elongation on that side= bending of shoot towards light
5.base covered by opaque shield= cell at base aren’t producing auxins= shoot grows towards light
6.tip separated by gelatine block= gelatine is permeable allowing auxin to diffuse down= plant bends towards light - tip separated by mica= impermeable= auxin can’t diffuse= plant grows up
how did Went’s experiment prove that a chemical messenger exists and stimulates phototropic response
- control agar block with no auxin= to prove no affect of agar on growth
- agar block with auxin covering entire tip= plant grows upwards
- agar block covering right side of plant= auxin diffuses down that side and elongates those cells= bends in opposite direction
- repeat on left side
how do auxins impact roots and geotropism
-auxin accumulates on the lower side of the root tip
-accumulation of high conc of auxin inhibits cell elongation
upper cells elongate and root tip grows downwards
what is apical dominance and how does auxin cause this,how does this change as plant grows taller, what is the apical bud
the plant grows only from the tip, high concentration of auxin in shoot tip inhibits the growth of lateral buds
-further down the stem there is less auxin= destroyed as cell matures= so lateral shoots can grow
-shoot tip= apical bud
what is a survival advantage of apical dominance
-prevents side shoots shading the shoot tip and diverting energy from growth of main stem= can grow fast and out compete other plants for light
what are synergistic and antagonistic effects of gibberellins with auxin on apical dominance
synergistic= work together to promote stem elongation
antagonistic= promote side shoot growth
what are synergistic and antagonistic effects of abscisic acid with auxin on apical dominance
synergistic- high auxin in the shoot keeps abscisic acid levels high in the buds- abscisic acid inhibits bud growth
antagonist= abscisic acid inhibits seed germination and growth
what happens to abscisic acid when the tip is removed
tip removed= auxin removed= abscisic acid levels fill and lateral buds start to grow
what is the effects of auxin and cytokinin on apical dominance
cytokinins promote bud growth- antagonistic to auxins
an application of cytokinins to buds can promote growth overriding the inhibitory effects of auxin
what is the role gibberellins in seed germination
-gibberellins are released by embryo when seed is soaked in water
-gibberellins switch on the genes for synthesis of proteases and amylases= needed for germination
-amylases breaks down starch in the seed to form glucose for respiration
-ATP produced is used for growth to break out through the seed coat
-glucose is also used for protein synthesis
explain the role of auxin and ethene in leaf loss
auxins inhibit leaf loss= auxins are produced by young leaves, as leaves age they produce less auxin
ethene stimulates leaf loss-ethene is produced by ageing leaves, layer of cells separating the leaf from the rest of the plant (abscission zone)
-switched on genes that produce enzymes that digest the cells in the separation zone
