Module 5: Plant responses

Question 1

What two types of stimuli do plants respond to

Answer 1

Herbiovary and aboitic stimuli

abiotic stimuli can be things like water stress
heribory is when they are being eaten by insects

Question 2

Give examples of physical plant responses

Answer 2

Thorns, spikes, hairy leaves

Question 3

What are the chemical defences

Answer 3

Tannins: Bitter taste, toxic to insects
Alkaloids: bitter taste, poisonous to animals which can affect metabolism (nicotine and tobacco)
Pheromones: affect social behaviour of other members of the same species (callose deposition)

(top three on spec)
Terpenoids: toxic to insects and fungi (neurotoxins, repellants)
Volatile organic compounds: same as pheromones but affect other species, an example being attracting parasitic wasps which lay eggs on catapillars which kills them)

Question 4

What is the folding response

Answer 4

Mimosa pudioca

• fold leaves when they are touched
• this scares animals off
• or insects can slide or the fly of if they land on the leaves to prevent them from being eaten

(from the spec)

Question 5

What are the 4 stages of plant growth and development

Answer 5

Seed germination
cell elongation
apical dominance
stem elongation

Question 6

How does a seed germinate

Answer 6

1. Water being absorbed stimulates creation of gibberellin
2. this stimulates breakdown of proteins
3. amalyse is made which breaks starch into maltose which breaks down into glucose

Question 7

What chemical is involved in

seed germination and what does it do

Answer 7

Gibberellins stimulate production of digestive enzymes which release glucose from food stores
energy released fro seedling growth

Question 8

What happens during cell elongation and what chemical is involved

Answer 8

Meristemic cells realises auxin at the tip of the shoot
auxin binds to receptor, which allows hydrogen ions to be pumped into the cell
hydrogen ions cause ph to be lowered, which helps make the cell wall more flexible, which allows it to elongate
auxin leaves the receptor and is broken down by enzymes
protein channel closes and no more hydrogen can come in
so the cell wall becomes rigid again

Question 9

What happens during apical dominance and what hormone is involved

Answer 9

Auxins promote apical shoot growth going upwards
Auxins limits lateral shoot growth (stem that grows horizontally)
This allows all the shoots to better compete for light

Question 10

What happens during stem elongation and what hormone is involved

Answer 10

Gibberellins concentration is increased 
This promotes stem elongation 
which means we get a taller plant 
this helps it better compete for light
(more light, more photosynthesis)

Question 11

Why don;t farmers want plants with long stems

Answer 11

want to reduce waste

and it can prevent crop damage

Question 12

What kind of relationship does auxin and gibberlien have

Answer 12

synergic and antagonsit relationship

Question 13

What is phototropism

Answer 13

Growth of plant in response to light,

Question 14

How does phototropism occur

Answer 14

Unilateral light causes auxins to move laterally to the shaded side
higher auxin conc on shaded side
rate of growth higher on shade side
this means shoots are postively phototropic and they grow towards the light

Question 15

Why is phototropism important

Answer 15

ensures max rate of photosynthesis

Question 16

What is geotropism

Answer 16

plant growth in response to gravity

Question 17

How does geotropism occur

Answer 17

Auxins found on the bottom part of the root
conc of auxins mean less root growth so the top of the plant faster
this ensures that the roots grow downwards

Question 18

Name three other types of tropism

Answer 18

Hydrotropisms: plant growth towards the water

thermotropism: plant growths in response to temperature
thigmotropism: plant growth in response to contact with an object

Question 19

What are IAA and what parts of plant growth or delvelopment are they are part of

Answer 19

An auxin that is produced in tips of shoots and roots (meristem)

• help with cell elongation
• maintain apical dominance (promotes apical growth so the vertical stem, and it inhibits the lateral shoots
• involved in phototropism and geotropism

Question 20

How did they find out about IAA

Answer 20

check the textbook

Question 21

What do auxins inhibit?

Answer 21

• Can inhibit fruit ripening (high level of auxins, the fruit won’t be ripe)
• can inhibit abscission (the falling fo leaves)

Question 22

How does ethene promote leaf loss in decidous plants

Answer 22

• proudced by aging leaves
• phyotchons dtect low levelsof light
• auxin conv decreases, ethene increase
• layer of cells called absicion layer develops at the bottom of the stalk
• the absiccion layer seperates leaf from the rest of the plant
• ethene stimulates cells in the abscission layer to produce digestive enzymes which breaks the cell wall, causes leaf to fall off

Question 23

What does ethene promote

Answer 23

• promotes abscission (leaf loss)

- promotes fruit ripening

Question 24

What kind of realtionship does auxins and ethene have

Answer 24

antagonistic realtionship

Question 25

What is the role of gibberrelins

Answer 25

• Promotes stem elongation (helps plant grow upwards)
• can promote seed germination
• stimulate pollen tube growth during fertilisation

Question 26

What is the role of abscisic acid (ABA)

Answer 26

• maintain dormancy of seeds (stops seed from germinating)
• stimulates protective measures or responses
  - antifreeze
  - stomatal closure (to prevent water loss)

Question 27

How does ABA trigger stomatal closure

Answer 27

1. ABA binds to recpectors on guard cell membranes
2. causes ion channels to open
3. calcium ions enter cytosol from vacoule
4. increased conc of calcium ions in cytosol causes other ion channels to open (pottassium channels)
5. raises water potential of the cell
6. Water leaves gaurd cells vai osmosis
7. guard cells become flaccid and stomata close

Question 28

What evidence have scientists found to find plant hormones

Answer 28

mutate genes that make a hormone
disrupt production pathway
cut shoot tip

Question 29

What are the commerical uses of plant hormones

Answer 29

Ethene is used to rippen fruit (an example is bannas they are picked when they are unripe, so when they arrive at peoples home they are ripe)

Auxins

• can be used a weed killers, this makes weeds proudce long stems and less leaves which means they die due to a lack of food)
• can be used a rooting hormone (can use cuttings with rooting powder to grow many new plants)