plant responses

Question 1

why do plants need to respond to their environment

Answer 1

avoid abiotic stress

maximise photosynthesis

avoid grazing

obtain more materials

Question 2

why is it hard to examine plant hormones

Answer 2

they work at very low concs

multiple interactions between different chemical control systems means we cannot directly measure the effect of a hormone

Question 3

give examples of physical defences

Answer 3

thorns

spikes

strings

Question 4

give examples of chemical defences

Answer 4

tannins
bind to enzymes to inactivate them

alkaloids

pheromones
absorbed by leaves to stimulate cellulose formation

Question 5

describe the action of ethene

Answer 5

speeds up ripening

promotes fruit drop

promotes lateral growth

Question 6

describe the action of abscisic acid

Answer 6

stimulates stomata closing

maintains dormancy of seeds (antagonist to gibberellin)

Question 7

describe the action of gibberellin

Answer 7

involved in seed germination

causes stem elongation
affects the length of the internodes

Question 8

describe research support for gibberellins

Answer 8

mutant varieties bred to not produce gibberellin don’t germinate

if gibberellin inhibitors are applied, they don’t germinate

Question 9

describe the action of auxins (indoleacetic acid)

Answer 9

made in tips of shoots and roots

promotes shoot growth and inhibit root growth (depending on its conc)

suppresses lateral shoot growth

Question 10

describe the auxin mechanism of cell elongation

Answer 10

binds to receptors on the c.s.m causing a fall in pH so the optimal pH for enzymes to keep cell wall flexible

cells absorb water and vacuoles form and enlargen

as cells mature, auxin is destroyed

so pH rises, those enzymes denature and the cells become rigid

Question 11

describe apical dominance caused by auxin

Answer 11

if the apical shoot is removed, there’s no auxin
so lateral shoots grow faster

if apical shoot is removed
amount of auxin reaching the root is reduced
root growth slows and stops
(high auxin conc inhibits root growth)

Question 12

define synergism

Answer 12

different hormones work together and complement each other giving a greater response than on their own

Question 13

define antagonism

Answer 13

describes hormones with opposite effects

the balance between them determines the response of the plant