plant responses Flashcards
what do plants respond to?
- competitors
- temp
- soil pH
- light
- gravity
- pathogens
- wind
-water potential of soil
what is a tropism?
- a directional growth response to a particular stimulus
- can be positive or negative
examples of tropisms
- phototropism : light
- geotropism/gravitropism : gravity
- chemotropism : chemicals
- thigmotropism : physical content
- hydrotropism : water
what is a nastic response?
non-directional response to an external stimuli (e.g. thigmotropism)
physical response of phototropism
shoot grows towards light
physical response of geotropism
root grows towards gravity
physical response of chemotropism
part of plant grows towards chemicals
physical response of thigmotropism
plant grows towards physical contact
survival advantage of phototropism
increases height of leaves for efficient photosynthesis
survival advantage of geotropism
- helps to anchor plants
- helps roots / plant get mineral ions and water
survival advantage of chemotropism
- helps plant grow away from toxins
- helps plant find minerals
survival advantage of thigmotropism
increases growth towards light for efficient photosynthesis
how does the plant ensure that the hormones only act on target tissue?
- cell signals are sent out
- target tissue has complementary receptor
- specific hormones have specific shapes which can only bind to specific receptors
by what transport methods will the hormones be transported around the plant?
- cell sap
- diffusion
- active transport
- translocation in phloem
role of hormone ethene / ethylene in plants
- fruit ripening
- leaf abscission
role of hormone auxin
- cell elongation (e.g. pollen tube growth)
- inhibition if lateral roots and leaf abscission (cutting off)
- apical dominance
- phototropism
role of hormone gibberellins
- germination
- stem growth
- stem elongation
role of hormone ABA (abscisic acid)
- inhibits germination and seed growth
- stomatal closure
role of hormone cytokinins
- mitosis
- delaying old age (senescence)
- overcomes apical dominance
- cell expansion
what is synergism?
when different hormones give a better response when working together than they would on their own
what is antagonism?
when the substances have opposite effects so the balance between them determines the response of the plant
physical defenses to herbivory
- calls elise plugs up phloem
- bark
- thorns / spikes
- sap
- tylose plugs xylem
- lignin thickening
- waxy cuticle
chemical defences to herbivory
- tannins - taste bitter to herbivores
- alkaloids - nitrogen containing compounds
- terpenoids - antibacterial and anti fungal cells
- pheromones - influence social behaviours
describe auxin (IAA)
- produced at the apex (top) of the meristem
- transported by active transport or diffusion to the “zone of elongation”
- conc if auxin determines the effect
describe auxin in geotropism
- low conc of auxin in roots increase root growth
- high conc inhibits cell elongation in the roots
explain how auxin is transported via active transport
- auxin activates the H+ pump and is moved into the cell wall
- the pH lowers and activates expansin enzymes
- expansins break H bonds in cellulose fibrils
- water moves into cell, elongating it
result of unilateral light shining towards plant shoot
shoot bends towards light
- as shoot is positively phototropic
-bending occurs behind the tip
result of shoot tip removed when light is shone
no response
- as the top must either detect the stimulus or produce the messenger (or both) as it’s removal prevents any response
result of lightproof cover placed over intact shoot tip
no response
- the light stimulus must be detected by the tip
result of thin, impermeable barrier of mica on one side of tip when light is shone
movement of chemical down the shaded side
bends towards light
- mica on the illuminated side of shoot allows the auxin to only pass down the shaded side where it increases growth and causes bending
result of mica inserted on shaded side
movement of chemical down its shaded side is prevented by mica
no response
effect of tip separated by mica
-auxin is stuck in tip
- cant move down shady side
result of gelatin block separating tip
movement of chemical down shaded side
bends towards light
- gelatin allows chemicals to pass through it but not electrical messages, the bending which occurs must be due to a chemical passing from the tip
difference between gelatin and mica
mica is non porous
gelatin is porous
what is apical dominance?
inhibition of side shoots
cause of apical dominance
the presence of auxin
what does abscisic acid do in apical dominance?
it inhibits bud growth.
- high levels of auxin maintain the high levels of abscisic acid in the bud, inhabiting the growth
if the apex of the shoot is removed how might this effect apical dominance?
- abscisic acid decreases
effect of cytokinins on apical dominance
- promote bud growth and can override the effect of apical dominance
- high levels of auxins in tissues cause cytokinins to be transported to those tissues
what does gibberellic acid cause?
- stem elongation and therefore tall plants
- seed germination
- stimulate pollen tube growth in fertilisation
explain how gibberellic acid causes stem elongation
- dominant Le gene is expressed
- produces enzyme that converts G20 to gibberellic acid (G1)
- promoting stem elongation
if you mutated the Le gene, what effects could you have on the phenotype of the plant and why?
- shorter stem
- enzyme not produced
- cant convert G20 to G1
why do seeds remain dormant until the right conditions occur for it to germinate?
- so energy is not wasted trying to grow in bad conditions
- as seeds need water and nutrients
when seeds absorb water what is produced and transported? what is enabled?
- gibberellin is produced and transported to the endosperm of the seeds
- it enables the production of amylase
what reaction does amylase catalyse?
starch into maltose
why does the product of amylase being catalysed promote germination of the seed?
glucose is used as food for plants. the seed can grow a leaf
6 commercial uses of plant hormones
- brewing
- sugar production
- decaying yellowing of leaves
- plant breeding
- ethene
- auxins
what plant hormone is involved in the germination of seeds?
gibberellins
what plant hormone is involved in stem elongation?
gibberellins + auxin
what can cytokinins delay and why is this good?
delay leaf senescence so plants and vegetables remain green for longer
what can be used for cell division, lateral shoot growth and lead growth?
cytokinins
how can auxins be used a herbicide?
a high conc stop plants from growing
a low conc stop plants from growing
