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A level Biology - Regular > Chapter 16 - Plant responses > Flashcards

Chapter 16 - Plant responses Flashcards

1
Q

Why do plants need specialised responses ?

A

They live in dynamic systems; they must respond to constant abiotic stresses

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2
Q

What are the key limitations to plants as oppose to animals ?

A
  • Plants are rooted and have no rapid nervous system hence must work in chemical coordination
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3
Q

What are the 4 main examples of Plant Hormones ?

A

1 - Auxins
2 - Gibberelin
3 - Ethene
4 - ABA - Abscisic acid

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4
Q

What is the function of Auxin ?

A
  • Controls cell elongation
  • Prevents leaf fall
  • Releases Ethene
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5
Q

What is the function of Gibberelin ?

A
  • Causes stem elongation and mobilisation of food stores
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6
Q

What is the function of Ethene ?

A
  • Causes fruit ripening and promote leaf fall
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7
Q

What is the function of ABA Abscisic acid ?

A
  • Maintains dormacy of seeds and buds
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8
Q

What do plants use these hormones for alltogether ?

A

For plant growth

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9
Q

How does plant growth occur ?

A

In 3 steps :
1 - Seed germination
2 - Cell elongation
3 - Apical Dominance/Stem elongation

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10
Q

How does plant growth occur ?

A

In 3 steps :
1 - Seed germination
2 - Cell elongation
3 - Apical Dominance/Stem Elongation

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11
Q

What are the steps of seed germination ?

A

(Gibberelin is the main hormone)
- Seed absorbs water and allows embryo to produce Gibberelin
- Gibberelin stimulates production of digestive enzymes to break down seeds food source for resp. to make ATP which is used to build materials by breaking through seed coating

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12
Q

What is the food source in Dicot seeds and Monocot seeds ?

A

Dicot = Cotyledons
Monocot = Endosperm

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13
Q

What is the experimental evidence to show Gibberelins link to seed Germination ?

A
  • Mutant varieties with no Gibberelins do not germinate
  • I Gibberelins biosynthesis inhibitants are applied - Seeds do not germinate
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14
Q

What are the steps for Cell elongation ?

A

1 - Meristematic cells produce Auxins, which diffuse towards zone of Elongation down conc. gradient
2 - Auxin binds to receptors in cell to open Protein channels that are specific to Hydrogen ions
3 - H+ ions diffuse into cell to lower pH
4 - Low pH causes cellulose to become flexible
5 - H2O moves into the cell without causing tugidity
6 - Cells elongate as large permanent vacuole is formed and Auxin leave receptors and are broken down via enzymes
7 - Protein channels close to prevent more H+ diffusion
8 - pH rises to normal and cell becomes rigid

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15
Q

What is Apical Dominance ?

A
  • Auxin promotes apical shoot growth
    and supresses lateral shoot growth
  • Allows all lateral shoots to get light

Tip shoots produce auxin
Lateral shoots produce auxin

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16
Q

What is the experimental evidence to support Auxins role in Apical dominance ?

A
  • Apical shoot being removed = Meristematic cells removed = No Auxin = Lateral shoots grow large = Apical shoot reapplied = Lateral shot growth inhibited
17
Q

What are the steps of Stem Elongation ?

A

inc. Conc. of Gibberelin = Increased size of Internodes = Taller plants = Better competing for light

18
Q

Why would stem elongation be limited ?

A
  • Decreases waste as stem is not edible to humans
  • Prevents crop damage by bad weather
19
Q

What is synergism and what is Antagonism ?

A

Synergism = Interaction of different hormones working together
Antagonism = Responses have opposing affects; creating a balance

20
Q

What are the 3 main abiotic stresses for plants ?

A

1 - Change in daylight
2 - Freezing
3 - Water loss

21
Q

How do plants respond to changes in daylight ?

A

Phytochromes act as kinases and interact with transcription factors; affecting genes that produce Auxin = affects ethene production when they detect falls in LI

22
Q

What are the steps to the responses o change in daylight ?

A

1 - Fall in light is detected; resulting in decreased Auxin prod.
2 - Increased Ethene levels produced in the leaf
3 - Ethene activates genes in cells present in abscission zone to produce digestive enzymes to break down cell walls
4 - Enzymes digest Cell wall in separationo zone
5 - Vascular bundles in protective layer are sealed off

23
Q

Why do plants respond to changes in light intensity by cutting off their leafs ?

A
  • Reduces energy needed to maintain leaves
  • Fallen leaves insulate roots
  • Rotten leaves provide minerals to plants
24
Q

How do plants respond to freezing ?

A
  • If temp drops = membranes of plants will crack and plants will die

1 - Cytoplasm and sap in vacuole contains solutes that lower freezing point
2 - Some plants produce sugars, polysaccharides and amino acids to act as an antifreeze

25
Q

How do plants respond to water loss ?

A

1 - Roots detect lack of water
2 - ABA travels to leaves and binds to receptors on guard cells
3 - Ions move out of guard cells to decrease Water potential on the outside
4 - H2O leaves via osmosis
5 - Guard cells become flaccid (plasmolysed) and close the stomata this decreases transpiration rate hence lower evaporation

26
Q

What are the plants responses to Herbivory ?

A

1 - Physical defences that are innate such as thorns spikes and hairy leaves
2 - Chemical defences

27
Q

What are the 4 main chemicals used in chemical defences ?

A

1 - Tannins : Bitter tast, toxic to insects
2 - Alkaloids : Bitter taste, poisonous to animals
3 - Terpenoids : Act on neurotoxins + repellents
4 - Pheromones : Chemical that is released out of the same species by affecting their social behavious

28
Q

What do volatile organic compounds in plants do ?

A
  • Same as pheomones but affect other species - to signal to predators that herbivores are around
29
Q

What physical defence does mimosa pudica have ?

A
  • Folding response when leaves are touched to scare herbivores and kakes insects slide off
30
Q

What is Tropism and nastic movements ?

A

Tropic = Movement in reponse to a stimuli
Nastic = Non directional movements

31
Q

How does phototropism occur ?

A

1- Unilateral light causes Auxins to move laterally to the shoot tip (Shaded side)
2 - [Auxin] is higher on shaded side
3 - Causes cell elongation to occur on the shaded side
4 - Hence, shoot will grow towards light

32
Q

How does phototropis, affect roots ?

A

Roots undergo negative phototropism
- As roots work best in soil/dark areas
- Mechanism works the same however Auxins cause inhibition of root growth

33
Q

How does Geotropism occur ?

A
  • Auxins fall to the bottom parts of shoots and roots due to gravity
    In roots :
    Positive Geotropism
    1 - [Auxin] increase in roots
    2 - Root growth is inihibited hence for top section undergoes cell elongation = roots bend downwards
    In shoot :
    Negative Geotropism
    1 - [Auxin] Increases = Shoot growth is promoted hence bottom section of shoot grows and bends leaf towards light

A level Biology - Regular (14 decks)

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