Plant Hormones/responses

Question 1

Example of plant hormones

Answer 1

• auxin
• ethene
• gibberellins
• ABA

Question 2

Auxin

Answer 2

• controls cell elongation
• prevent leaf fall
• growth of apical shoot (apical dominance)
• stimulate ethene production

Question 3

Apical Dominance

Answer 3

• stretch cell wall
• supress the growth of lateral shoots
• low concentration can promote root growth

Question 4

Auxin Experiment

Answer 4

• cut off tip
• cover tip
• light on one side
• agar permeable block
• leave tip

Question 5

Gibberellins

Answer 5

• control stem elongation (effect length of internodes )
• seed germination (absorb water which produces enzymes to break down food stores, to produce ATP)
• control the switching on and off of genes

Question 6

Ethene

Answer 6

• causes fruit ripening
• promotes abscission (leaf loss)

Question 7

ABA

Answer 7

• abscisic acid
• stimulates stomatal closure
• maintains dormancy of seed and buds
• stimulates anti freeze

Question 8

Abiotic stress

Answer 8

• leaf loss (abscission)
• daylight sensitivity
• leaf fall
• preventing freezing
• stomatal control

Question 9

Leaf loss

Answer 9

• light and temperature affect rate of photosynthesis
• amount of glucose required for respiration to maintain the leaves
• deciduous trees lose their leaves to remain dormant
• more energy efficient to lose leaves

Question 10

Daylight sensitivity

Answer 10

• different plant responses are affected by the photoperiod
• sensitivity to day length results from a light sensitive pigment

Question 11

Leaf fall (abscission)

Answer 11

• lengthening for dark periods triggers leaf fall and dormancy over winter months
• falling light levels decreases auxin levels by producing ethene
• vascular bundles are sealed up

Question 12

Preventing freezing

Answer 12

• produce sugars, amino acids and proteins to prevent the cytoplasm from freezing

Question 13

Stomatal closure

Answer 13

• controlled by ABA
• under times of stress stomata close
• soil water levels decrease and roots produce ABA which decreases the WP and turgor levels so transpiration losses decrease

Question 14

Responses to herbivory

Answer 14

• physical
• chemical

Question 15

Physical responses

Answer 15

• thorns
• spikes
• spiny leaves
• stings
• inedible tissue

Question 16

Chemical responses

Answer 16

• tannins
• alkaloids
• pheromones
  -folding in response to touch
• terpenoids

Question 17

Tannins

Answer 17

• 50% of dry weight
• bitter taste
• toxic to insects
• e.g oak and walnuts

Question 18

Terpenoids

Answer 18

• form essential oils
• pyrethrin = acts as an insect neurotoxin and interferes with there nervous system
• citronella

Question 19

Pheromones

Answer 19

• affect social behaviour of other members of the same species
• maple trees = release callose which protects them
• produce VOC (volatile organic compound) = chemical signals to defend themselves

Question 20

Folding due to touch

Answer 20

• e.g Mimosa pudica = leaves fold down if touched due to K ions moving into specific cells with osmotic water movement

Question 21

Alkaloids

Answer 21

-nitrogenous and bitter tasting
- affect metabolism of the herbivore
- e,g nicotine and caffeine

Question 22

Tropism

Answer 22

• phototropism
• geotropism

Question 23

Phototropism

Answer 23

• growth of plants towards or away from light
• shoots are positively phototrophic
• roots are negatively phototropic

Question 24

Geotropism

Answer 24

• growth of a plant in response to gravity
• shoots are negatively geotropic
• roots are positively geotropic

Question 25

Commercial used of plant hormones

Answer 25

- control ripening (ethene and auxin ) - hormone rooting powder ( auxin ) - hormone weed killer (auxin) - production of seedless fruit (auxin) - prevent abscission (auxin)