16.1 Plant hormones

Question 1

what is a tropism?

Answer 1

a response to a stimulus

Question 2

what is auxin used for?

Answer 2

controlling cell elongation
preventing leaf fall
maintaining apical dominance
stimulating ethene release
fruit ripening

Question 3

what is gibberellin used for?

Answer 3

causes stem elongation
stimulates pollen tube growth
seed germination
lateral shoot growth

Question 4

how is the relationship between auxin and gibberellin synergistic?

Answer 4

they work together to make a plant tall

Question 5

how is the relationship between auxin and gibberellin antagonistic?

Answer 5

gibberellin stimulates lateral shoots growth while auxin inhibits it

Question 6

what is ethene used for?

Answer 6

causes fruit ripening
promotes abscission

Question 7

what is ABA used for?

Answer 7

maintain seed dormancy
stomatal closing control
anti-freeze measures

it inhibits gibberellin

Question 8

how are gibberelins involved in seed germination?

Answer 8

when seed absorbs water, embryo is activated and gibberellins are produced

gibberellins stimulate production of enzymes which break down food stores
the plant uses food stores to produce ATP to grow

gibberellins also switch on genes which code for amylases and proteases which are required for seed germination

Question 9

what evidence supports gibberelins being involved in seed germination?

Answer 9

mutant seeds which lack the gene allowing for gibberellin production did not germinate but when gibberellins were added externally they germinated

if gibberellin inhibitors are added to a plant they don’t germinate but once removed they germinate

Question 10

what inhibits Gibberellins?

Answer 10

ABA

Question 11

where is auxin produced?

Answer 11

in the tips of the roots and shoots

meristems

Question 12

what are the 3 main effects of auxin in plant growth?

Answer 12

stimulate growth of the apical shoot

high concentrations suppress the growth of lateral shoots

low concentrations in the root promote root growth

Question 13

what evidence is there to show that auxins stimulate shoot growth?

Answer 13

presence of auxin makes the cell wall stretch more easily

auxin binds to receptor sites in the cell surface membrane causing the pH to fall to an optimum pH level to keep the walls flexible and plastic

once plant matures, auxin is destroyed and the wall becomes rigid

Question 14

what causes the plant membranes to be plasticy or rigid?

Answer 14

enzymes

hence their activity is controlled by pH which is controlled by Auxin

Question 15

what is apical dominance?

Answer 15

when the central vertical shoot grows dominantly over the lateral branches

Question 16

how does auxin cause apical dominance?

Answer 16

auxin is in high concentration at the apical bud

this is where the most inhibition of lateral growth occurs

as you go down the plant, auxin concentration decreases
so less inhibition of lateral growth

so more growth of lateral shoots

Question 17

what evidence is there to show auxin suppressing the growth if lateral shoots?

Answer 17

if the apical shoot is removed, the lateral shoots grow faster as there is no auxin to inhibit their growth
BUT
if auxin is reapplied externally growth is stopped

Question 18

how do auxin concentrations increase root growth?

Answer 18

low auxin concentration in the roots means more root growth

Question 19

how do auxin concentrations decrease root growth?

Answer 19

high auxin concentration in the roots inhibits growth of roots

Question 20

how do gibberellins affect elongation?

Answer 20

they affect the length of the internodes between the leaves on a stem

Question 21

what evidence shows the affect of gibberellins on stem elongation?

Answer 21

if gibberellin action is interrupted the plant is much shorter

length of internodes decreases

DWARF PLANTS

Question 22

what is synergism?

Answer 22

when hormones compliment eachother

Question 23

what is antagonism?

Answer 23

when hormones inhibit eachother