plant responses

Question 1

what do plants respond to?

Answer 1

• competitors
• temp
• soil pH
• light
• gravity
• pathogens
• wind
  -water potential of soil

Question 2

what is a tropism?

Answer 2

• a directional growth response to a particular stimulus
• can be positive or negative

Question 3

examples of tropisms

Answer 3

• phototropism : light
• geotropism/gravitropism : gravity
• chemotropism : chemicals
• thigmotropism : physical content
• hydrotropism : water

Question 4

what is a nastic response?

Answer 4

non-directional response to an external stimuli (e.g. thigmotropism)

Question 5

physical response of phototropism

Answer 5

shoot grows towards light

Question 6

physical response of geotropism

Answer 6

root grows towards gravity

Question 7

physical response of chemotropism

Answer 7

part of plant grows towards chemicals

Question 8

physical response of thigmotropism

Answer 8

plant grows towards physical contact

Question 9

survival advantage of phototropism

Answer 9

increases height of leaves for efficient photosynthesis

Question 10

survival advantage of geotropism

Answer 10

• helps to anchor plants
• helps roots / plant get mineral ions and water

Question 11

survival advantage of chemotropism

Answer 11

• helps plant grow away from toxins
• helps plant find minerals

Question 12

survival advantage of thigmotropism

Answer 12

increases growth towards light for efficient photosynthesis

Question 13

how does the plant ensure that the hormones only act on target tissue?

Answer 13

• cell signals are sent out
• target tissue has complementary receptor
• specific hormones have specific shapes which can only bind to specific receptors

Question 14

by what transport methods will the hormones be transported around the plant?

Answer 14

• cell sap
• diffusion
• active transport
• translocation in phloem

Question 15

role of hormone ethene / ethylene in plants

Answer 15

• fruit ripening
• leaf abscission

Question 16

role of hormone auxin

Answer 16

• cell elongation (e.g. pollen tube growth)
• inhibition if lateral roots and leaf abscission (cutting off)
• apical dominance
• phototropism

Question 17

role of hormone gibberellins

Answer 17

• germination
• stem growth
• stem elongation

Question 18

role of hormone ABA (abscisic acid)

Answer 18

• inhibits germination and seed growth
• stomatal closure

Question 19

role of hormone cytokinins

Answer 19

• mitosis
• delaying old age (senescence)
• overcomes apical dominance
• cell expansion

Question 20

what is synergism?

Answer 20

when different hormones give a better response when working together than they would on their own

Question 21

what is antagonism?

Answer 21

when the substances have opposite effects so the balance between them determines the response of the plant

Question 22

physical defenses to herbivory

Answer 22

• calls elise plugs up phloem
• bark
• thorns / spikes
• sap
• tylose plugs xylem
• lignin thickening
• waxy cuticle

Question 23

chemical defences to herbivory

Answer 23

1. tannins - taste bitter to herbivores
2. alkaloids - nitrogen containing compounds
3. terpenoids - antibacterial and anti fungal cells
4. pheromones - influence social behaviours

Question 24

describe auxin (IAA)

Answer 24

• produced at the apex (top) of the meristem
• transported by active transport or diffusion to the “zone of elongation”
• conc if auxin determines the effect

Question 25

describe auxin in geotropism

Answer 25

- low conc of auxin in roots increase root growth - high conc inhibits cell elongation in the roots

Question 26

explain how auxin is transported via active transport

Answer 26

1. auxin activates the H+ pump and is moved into the cell wall 2. the pH lowers and activates expansin enzymes 3. expansins break H bonds in cellulose fibrils 4. water moves into cell, elongating it

Question 27

result of unilateral light shining towards plant shoot

Answer 27

shoot bends towards light - as shoot is positively phototropic -bending occurs behind the tip

Question 28

result of shoot tip removed when light is shone

Answer 28

no response - as the top must either detect the stimulus or produce the messenger (or both) as it’s removal prevents any response

Question 29

result of lightproof cover placed over intact shoot tip

Answer 29

no response - the light stimulus must be detected by the tip

Question 30

result of thin, impermeable barrier of mica on one side of tip when light is shone

Answer 30

movement of chemical down the shaded side bends towards light - mica on the illuminated side of shoot allows the auxin to only pass down the shaded side where it increases growth and causes bending

Question 31

result of mica inserted on shaded side

Answer 31

movement of chemical down its shaded side is prevented by mica no response

Question 32

effect of tip separated by mica

Answer 32

-auxin is stuck in tip - cant move down shady side

Question 33

result of gelatin block separating tip

Answer 33

movement of chemical down shaded side bends towards light - gelatin allows chemicals to pass through it but not electrical messages, the bending which occurs must be due to a chemical passing from the tip

Question 34

difference between gelatin and mica

Answer 34

mica is non porous gelatin is porous

Question 35

what is apical dominance?

Answer 35

inhibition of side shoots

Question 36

cause of apical dominance

Answer 36

the presence of auxin

Question 37

what does abscisic acid do in apical dominance?

Answer 37

it inhibits bud growth. - high levels of auxin maintain the high levels of abscisic acid in the bud, inhabiting the growth

Question 38

if the apex of the shoot is removed how might this effect apical dominance?

Answer 38

- abscisic acid decreases

Question 39

effect of cytokinins on apical dominance

Answer 39

- promote bud growth and can override the effect of apical dominance - high levels of auxins in tissues cause cytokinins to be transported to those tissues

Question 40

what does gibberellic acid cause?

Answer 40

- stem elongation and therefore tall plants - seed germination - stimulate pollen tube growth in fertilisation

Question 41

explain how gibberellic acid causes stem elongation

Answer 41

- dominant Le gene is expressed - produces enzyme that converts G20 to gibberellic acid (G1) - promoting stem elongation

Question 42

if you mutated the Le gene, what effects could you have on the phenotype of the plant and why?

Answer 42

- shorter stem - enzyme not produced - cant convert G20 to G1

Question 43

why do seeds remain dormant until the right conditions occur for it to germinate?

Answer 43

- so energy is not wasted trying to grow in bad conditions - as seeds need water and nutrients

Question 44

when seeds absorb water what is produced and transported? what is enabled?

Answer 44

- gibberellin is produced and transported to the endosperm of the seeds - it enables the production of amylase

Question 45

what reaction does amylase catalyse?

Answer 45

starch into maltose

Question 46

why does the product of amylase being catalysed promote germination of the seed?

Answer 46

glucose is used as food for plants. the seed can grow a leaf

Question 47

6 commercial uses of plant hormones

Answer 47

1. brewing 2. sugar production 3. decaying yellowing of leaves 4. plant breeding 5. ethene 6. auxins

Question 48

what plant hormone is involved in the germination of seeds?

Answer 48

gibberellins

Question 49

what plant hormone is involved in stem elongation?

Answer 49

gibberellins + auxin

Question 50

what can cytokinins delay and why is this good?

Answer 50

delay leaf senescence so plants and vegetables remain green for longer

Question 51

what can be used for cell division, lateral shoot growth and lead growth?

Answer 51

cytokinins

Question 52

how can auxins be used a herbicide?

Answer 52

a high conc stop plants from growing a low conc stop plants from growing