Plant responses Flashcards
1
Q
synergy
A
hormones amplifying each others’ effect or working together
2
Q
antagonism
A
hormones cancelling out each others’ effects
3
Q
action of gibberellin in seed germination
A
- water absorbed and embryo activated
- embryo starts to produce gibberellins which switch on gene for enzyme production such as proteases and amylase
- these enzymes break down food stores in seed eg. starch to maltose to glucose
- ATP available for growth of embryo to break through the seed coat - seed no longer dormant
4
Q
abscisic acid action - seed dormancy
A
- opposite effect to gibberellins
- maintains seed dormancy by inhibiting amylase production
- supresses growth
5
Q
evidence of gibberellin action in germination
A
- seeds with mutation to not make gibberellin don’t germinate
- when gibberellins added to seeds externally, they germinate
- if chemicals that inhibit gibberellins applied to seeds, they don’t germinate
6
Q
action of gibberellin in stem elongation
A
- affect the length of internodes (regions between leaves on stem)
- alters properties of cell wall, lowering water pot of cell and allowing water uptake and therefore increase in cell volume
- low gibberellin levels - stems are shorter which reduces waste and makes plants less vulnerable to weather damage
7
Q
evidence of gibberellin in stem elongation
A
- dwarf plants have been found to have low levels of gibberellin
- if dwarf plants treated with gibberellins, they grow to same height as normal plants
8
Q
action of auxins on growth of shoots
A
- auxin molecules (eg. IAA) bind to receptor site in plant cell membrane, causing pH to fall to 5
- pH 5 is optimal for enzymes needed to pump protons into cells wall causing bonds between microfibres to loosen - cell wall flexible
- K+ channels open and K+ enters cytoplasm
- water moves down water pot grad and enters cytoplasm
- when cells mature, auxin levels fall
- therefore pH rises so enzymes stop working so the cell wall becomes more fixed and can no longer grow and expand
9
Q
apical dominance meaning and reasoning
A
- apical dominance - auxins produced at growing tip of apex causing stem to grow upwards
- high conc auxin - suppresses lateral growth
- further down stem - less auxin so buds can grow laterally
- if apical shoot removed - auxin producing cells removed and apical dominance stops
- best for plants to grow upwards towards light to maximise energy for photosynthesis
- sideways growth not so useful - apical dominance caused by auxins ensures growth is upwards
10
Q
action of auxins in root growth
A
- low concentrations promote root growth
- up to a conc, the more auxin that reaches the roots, the more they grow
- auxin is produced in the root tips and is supplied to the roots in low conc from the shoot
- if shoot removed, less auxin reaches the roots and growth slows
- high auxin conc inhibits root growth
11
Q
phototropism
A
- +ve auxins accumulate on shaded side so shoot grows towards light - needs light for photosynthesis
- -ve roots grows away from light - anchors plant into ground
12
Q
geotropism
A
+ve roots grows towards gravity - anchors plant into ground
-ve shoot grows away from gravity - more light further up
13
Q
thigmotropism
A
+ve shoot grows towards a stimulus eg. wrapping around bamboo
-ve growing away from a stimulus eg. root growing away from a rock
14
Q
hydrotropism
A
+ve roots grow towards water source
-ve shoot grows away from water
15
Q
chemotropism
A
+ve roots growing towards region of mineral store in soil
-ve roots growing away from acidic region of soil
16
Q
experiment into phototropism - removing tip of coleoptile and covering with cap
A
- removed top of coleoptile and shoot didn’t grow towards light source - the tip must detect the stimulus or produce the messenger as its removal prevents the response
- he covered the tip with an opaque cap which also stopped it growing towards light - light stimulus detected by the tip
17
Q
experiment into phototropism - gelatin and mica sheet
A
- cut off tip of coleoptile and replaced it with thin layer of gelatin (permeable) between tip and stem
- stem grew towarss the light - a chemical could pass through gelatin, not an electrical impulse
- he put a thin mica sheet (impermeable) below tip of coleoptiles only on non-shaded side
- this didn’t prevent curvature -chemical must go to the shaded side to cause the shoot to grow on that side
- when mica sheet on shaded side - no curvature
- concluded that chemical is produced at tip then travels down shaded side - opposite side to stimulus causing growth on shaded side
18
Q
Paal’s experiment into phototropism - tip of coleoptile placed off centre
A
- side of coleoptile that tip placed on grew more causing it to curve
- this shows in the light, the phototropic response is caused by a hormone diffusing through the plant tissue stimulating growth
19
Q
Went’s experiment into phototropism - gelatin block
A
- cut tip of coleoptile placed on block of gelatin allowing the hormone to diffuse into it
- block placed on coleoptile off centre in the dark - stem grew on side that gelatin block placed on
- concluded that substance in gelatin block diffused in coleoptile causing cell elongation in that side
20
Q
effect of light on auxin
A
- the side of a shoot exposed to light contains less auxin that shaded side
- light causes auxinto move laterally across shoot - greater conc on shaded side
- stimulates cell elongation on shaded side - growth towards the light
21
Q
why do plants grow faster in the dark?
A
- a plants rapidly growing upwards to reach the light source makes sense for it to photosynthesise
- gibberellins - responsible for extreme elongation of internodes in darkness
- once exposed to light, more energy is used for photosynthesising, strengthening stems and overall growth
22
Q
geotropism in context of auxin
A
- shoots grow away from gravity - negative geotropism
- gravity causes auxin to accumulate on lower side of shoot, increasing rate of growth on lower side, causing shoot to grow upwards
- roots grow towards gravity (positive geotropism)
- in roots high auxin conc causes lower rate of cell elongation
23
Q
physical defences in plants
A
- spikes
- bark
- cell wall
24
Q
chemical defences in plants
A
- alkaloids - nitrogenous bitter tasting compound, many act as drugs eg. nicotine, caffeine, morphine, cocaine - usually interfere with metabolism
- tannins - very bitter tasting compounds to animals, toxic to insects - digestive enzyme inhibitors eg. in red wine
- terpenoids - can form essesntial oils and are toxic to insects eg. citronella as insect repellent
25
Q
pheromone
A
- chemical released that affects behaviour of other members of the same species
- eg. maple tree can release pheromones when being eaten to signal to other maple trees to release defence chemicals
26
Q
volatile organic compounds
A
- chemicals released that allow plants to communicate with other species
- eg. white cabbage produces chemical to attract parasitic wasp when being attacked by caterpillars. Wasp lays eggs in caterpillars which then get eaten alive
27
Q
why do some plants fold in response to touch?
A
- it scares off larger herbivores and disrupts small insects which land on the leaves
28
Q
leaf abscission - reasons
A
- deciduous plants drop their leaves seasonally
- cost of energy required to maintain anti-freeze chemicals in the leaves is greater than the glucose produced by photosynthesis in the winter (less light and low temps)
- a tree with leaves is also more likely to be affected by strong winter gales
29
Q
leaf abcission - process
A
- light levels drop, auxin levels drop, ethene levels rise - switching on genes for enzymes that digest cell walls
- cell walls in abscission zone (base of leaf stalk) get weaker
- vascular bundles sealed off
- fatty material is deposited in stem side of separation layer to form protective layer for when leaf falls off - prevents entry of pathogens
- cells in separation zone retain water causing strain on the outer layer
- this as well as strong winds and low temps causes the leaf to fall off the plant
30
Q
preventing freezing
A
- cytoplasm and vacuole sap contains sugars, polysaccharides, amino acids or proteins which lower the freezing point
- most species only produce these chemicals in the winter months and warm weather will reverse the changes
31
Q
photoperiodism
A
- plants are sensitive to a lack of light in their environment
- changes the break of dormancy, timing of flowering and when tubers are formed in prep for overwintering
- sensitivity of plants to day length is due to phytochrome - a light-sensitive pigment
32
Q
abscisic acid (ABA) on stomata
A
- leaf cells release ABA under abiotic stress
- roots also produce ABA during water stresses and it’s transported to the leaves
- ABA binds to receptors on membrane of guard cells causing change in ionic conc and reducing water pot of guard cell
- guard cells become less turgid and stomata close - reduces water loss by transpiration
33
Q
commercial use of ethene
A
- controlled ripening - stimulates fruit to ripen
- climacteric fruit - ripen after being harvested, requires ethene to ripen eg. banana, apple, avocado
- easier to transport when unripened as they don’t bruise as easily
- when ready for sale, ethene gas is released - all ripen at same rate, prevents wastage during transport, increases time for sales
- as ethene conc increases, CO2 conc increases as respiration rate increases
34
Q
commercial use of auxin (rooting powder)
A
- at low doses, auxin powder can stimulate growth of new roots in cuttings
- used in micropropogation - producing clones from a plant with desirable traits
35
Q
commercial use of auxin (selective weed killer)
A
- synthetic auxin in v high conc can be sprayed onto unwanted plants, causing increased metabolism and rapid growth - susceptible to pathogens and unstable - unsustainable so plant dies
- cost effective, low toxicity to animals
36
Q
cytokines commercial use
A
- prevent ripe fruit from ageing eg. lettuce
