plant responses

Question 1

auxin role

Answer 1

• control cell elongation
• prevents leaf abscission
• maintain apical dominance
• involved in tropism
• stimulate ethene release
• fruit ripening

Question 2

gibberellin

Answer 2

• cause stem elongation
• mobilisation of food stores in a seed at germination
• stimulates pollen tube growth in fertilisation

Question 3

ethene

Answer 3

• fruit ripening

- promotes abscission in deciduous tress

Question 4

ABA

Answer 4

• abscisic acid
• maintain dormancy of seeds + buds
• stimulates cold protective responses (antifreeze production + stomatal closure)

Question 5

experimental evidence for role of gibberellins in seed germination

Answer 5

• seeds that lack gene that enables them to make gibberellins do not germinate - if gibberellins are applied externally, they germinate normally
• if gibberellin biosynthesis inhibitors applied to seeds they don’t germinate - if inhibition is removed/gibberellins applied the seeds germinate

Question 6

auxin affect on pH and plant growth

Answer 6

• auxins such as IAA are growth stimulants
• tip of roots/shoots + meristems
• stimulate growth of apical shoot
• evidence : auxin affects plasticity of cell wall : CW stretches more easily
• auxins binds to specific receptor sites in plant CM
• pH decreases to 5
• optimum pH for enzymes to keep CW flexible and plastic
• when auxin conc = low (when cell matures)
• pH rises
• enzymes maintain plasticity inactive
• CW becomes rigid
• fixed in shape + size
• cells can’t expand/grow

Question 7

what is apical dominance

Answer 7

• auxin suppresses growth of lateral shoots
• results in apical dominance
• growth of main shoot
• stimulated by auxin produced at tip so grows quick
• lateral shoots inhibited by auxin moving up and down the stem
• down the stem = low conc of auxin = longer lateral shoots

Question 8

evidence of apical dominance

Answer 8

• apical shoot removed
• auxin producing cells removed
• no auxin
• lateral shoots grow faster
• auxin applied artificially = apical dominance is reasserted
  + lateral shoot growth = supressed

Question 9

auxin and root growth

Answer 9

• auxin conc = low
• promotes root growth
• more auxin in roots = more they grow
• apical shoot removed = less auxin reaching roots = root growth slows

Question 10

synergism

Answer 10

• diff hormones work together

- greater response

Question 11

antagonism

Answer 11

• substances have opposite effects

- E.g one promoting growth + one inhibiting

Question 12

abiotic stress

Answer 12

• non-living stresses that affect plants
• extreme temp
• high winds
• flood
• natural disasters

Question 13

biotic stress

Answer 13

• stress to plants caused by living organisms
• bacteria
• fungi
• virus
• insects
• weeds

Question 14

plant Reponses to abiotic stress

- leaf loss

Answer 14

• leaf loss in deciduous plants :
• lose leaves in winter (damaged by wind)
• remain dormant until temp rises
• glucose needed for resp to maintain leaves is greater than glucose produced in photosynthesis
• due to lack of light/low temp

Question 15

plant response to abiotic stress

- preventing freezing

Answer 15

• if cells freeze = membrane disrupted = die
• cytoplasm + sap in vacuole have solutes which lower the freezing point
• sugars/amino acids act as antifreeze
• protect cells from damage

Question 16

plant response to abiotic stress

- stomatal control

Answer 16

• open stomata = cool the plant
• water evaporates from cells in leaves in transpiration
• close stomata = conserve water
• close/open controlled by ABA
• leaf cells release ABA when under abiotic stress = stomata close

Question 17

ABA and water stress

Answer 17

• soil water conc fall
• roots produce ABA
• transported to leaves
• binds to receptors on PM of stomata guard cells
• ABA activated ionic conc changed of guard cells
• reduced water potential
• reduced turgor
• guard cells close stomata
• water lost by transpiration is reduced

Question 18

physical defence

Answer 18

• thorns
• spikes
• hairy leaves
• spiny leaves

Question 19

chemical defence

Answer 19

Tannins :

• phenol
• bitter taste
• puts animals off eating plants
• toxic to insects
• bind to digestive enzymes in saliva and inactivate
• in tea + red wine

alkaloids:

• bitter
• acts as drugs
• affect metabolism of animals = poisoning them
• caffeine, nicotine

Question 20

chemical defence - phermones

Answer 20

• affects social behaviour of other members of same species
• maples tree attacked by insects : releases pheromones absorbed by leaves on other branches
• leaves make chemicals (callose) to help protect them

Question 21

folding in response to touch

Answer 21

• Mimosa pudica
• contain toxic alkaloid
• stem has sharp prickles
• when leaves touches fold downwards + collapse
• scares larger herbivores
• dislodges small insects
• recover die to K+ ion and osmotic movements into specific cells

Question 22

phototropism

Answer 22

• IAA moves to more shaded parts of the shoots + roots
• uneven growth
• cell elongates
• shoot bends towards the light
• if IAA in roots growth is inhibited
• root bends away from light

Question 23

geotropism

Answer 23

• IAA moves to underside of shoots + roots
• uneven growth
• cells elongate and shoot moves upwards
• IAA in roots inhibits growth
• root grows downwards

Question 24

commercial uses of plant hormones

Answer 24

• ethene stimulates enzymes that break down CW
• break down chlorophyll
• convert starch into sugars
• fruits = soft + ripe
• auxins = selective weed killers
• auxins make weeds
• produce long stems instead of lots of leaves
• makes weeds grow too fast
• can’t get enough water/nutrients = die
• auxins = rooting hormones
• auxins make a cutting
• planted and grown in a new plant
• lots of the same plant can be grown quickly + cheaply from one plant.
• auxins produce seedless fruit