Plant responses Flashcards
(36 cards)
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 shoot 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
pheromone
- 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
volatile organic compounds
- 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
why do some plants fold in response to touch?
- it scares off larger herbivores and disrupts small insects which land on the leaves
28
leaf abscission - reasons
- 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
leaf abcission - process
- 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
preventing freezing
- 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
photoperiodism
- 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
abscisic acid (ABA) on stomata
- 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
commercial use of ethene
- 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
commercial use of auxin (rooting powder)
- 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
commercial use of auxin (selective weed killer)
- 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
cytokines commercial use
- prevent ripe fruit from ageing eg. lettuce
