5 - MZH - Plant responses Flashcards

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1
Q

State 2 ways in which plants use to produce coordinated responses

A
  • Chemical communication molecules (hormones)
  • Growth substances/ regulators
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2
Q

give 5 examples of plant reponses

A
  • Seed germinating in suitable conditions - ensure optical growth
  • Shoots growing upwards and roots downwards
  • Plants growing adaptively with respect to light and variations in water content of the soil
  • Responding to seasons in order to flower at the right time
  • Responding to predation or abiotic stress
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3
Q

Define Abiotic stress + example

A

Abiotic stress = Somethign that’s potentially harmful to a plant that’s natural but non-living

E.g. drought - water stress

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4
Q

Define Herbivory

A

Herbivory = Process of animals eating plants

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5
Q

What are pheromones?

A

Pheromones = A signalling chemical, released by one plant, that affects the response of others

If this plant releases pheromones into its environment neighbouring plants can start producing defensive chemicals befoe they themselves are attacked

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6
Q

Give an example of a plant responding to abiotic stress

A

Carrots:

Produce antifreeze at low temperatures

  • Proteins bind to ice crystals and lower the temperature that water freezez at ∴ stopping more ice crystals from growing
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7
Q

Different responses given by plants in response to herbivory and pathogenic microorganisms? (4)

A

Physical defences

Chemical defences - Tannins, alkaloids and pheromones

Leaf folding - Mimosa pudicans

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8
Q

Responses to herbivory/ pathogenic microorganisms:

Physical defences

A
  • Thorns
  • Spikes
  • Hairy leaves
  • Stings

Goal = Make themselves unappetising to predator

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9
Q

Responses to herbivory/ pathogenic microorganisms:

Chemical defences

A

Alkaloids:

  • Chemicals derived from amino acids and taste bitter, smell noxious or have poisonous characteristics that deter or kill herbivores
  • Located = outer leaves of stems and roots
    • E.g. Tobacco plants produce the alkaloid nicotine (which is poinsonous to many insects) in response to tissue damage

Tannins:

  • Tastes bitter
  • In some herbivores (cattle, sheep) they can bind to proteins in the gut, making the plant hard to digest

Pheromones = A signalling chemical, released by one plant, and can affect the responses of others

  • Some plants release alarm pheromones into the air in response to herbivore grazing. Allows nearby plants to detect these chemicals and start making chemical defences
  • When corn plants are eaten by caterpillars, the produce pheromones which attract parasitic wasps. These wasps lay their eggs in the caterpillars, which eventually kill them
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10
Q

Responses to herbivory/ pathogenic microorganisms:

Leaf folding

A

Mimosa pudicans - is a sensitive plant which has leaves that collapse in towards the stems if touched and are protects by sharp spines

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11
Q

Define Tropism

A

Tropism = Directional growth reponse of plants determined by a stimulus

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12
Q

What is the difference between a positive/ negative tropism?

A

Positive tropism = Respons towards the stimulus

Negative tropism = Response away from the stimulus

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13
Q

Name the 5 types of tropism you need to know and name the stimulus that accompanies each type of tropism

A
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14
Q

What are nastic responses?

Example?

A

Nastic responses = Non-directional responses to external stimuli e.g. collapsing of leaves on mimosa

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15
Q

Phototropism

How is it useful?

A

Positive phototropism = Plant shoot responding by growing towards light

  • Shoot phototropisms are controlled by plant hormones called Auxin e.g. IAA
  • For a plant to respond to light it needs a photoreceptor molecule that’s sensitive to light changes
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16
Q

Geotropism

How is it useful?

A
  • Roots grow towards the pull of gravity
  • Response anchors the roots
    • Helps them to support the above ground structures
    • Helps in the uptake of water and mineral salts
17
Q

Chemotropism

How is it useful?

A

On a flower pollen grains grow down the style, attracted to chemicals so they can enter the ovary and fertilisation can take place

18
Q

Thigmotropism

How is it useful?

A
  • Shoots of ivy and other climbing plants wind round other plants or solid structures to gain support
  • The tendrils of sweet peas wrap around objects they touch allowing the plant to gain support + climb
19
Q

Give the basic summary of the communication system of flowering plants (3)

A

Sensor (receptor) → Plant hormone → Effector

20
Q

Compare animal hormones and plant hormones

A
21
Q

List 3 ways in which plant hormones move around the plant?

A
  • Active transport
  • Diffusion
  • Mass flow in phloem and xylem vessels
22
Q

Name the 5 plant hormones you need to know

A

Cytokines

Abscisic acid (ABA)

Auxins e.g. IAA - Indoleacetic Acid

Giberellines

Ethene

23
Q

Plant hormones and their effects: (4)

Cytokines

A
  • Promote cell division
  • Delay leaf senescence
  • Overcome apical dominance
  • Promote cell expansion
24
Q

Plant hormones and their effects: (3)

Abscisic acid (ABA)

A
  • Inhibits seed germination + growth
  • Causes stomatal closure when the plant is stressed by a shortage of water
  • Stimulates cold protective responses
    • e.g. production of antifreeze
25
Q

Plant hormones and their effects: (3) + example

Auxins

A

E.g. IAA - Indoleacetic acid

  • Promote cell elongation (taller!)
  • Inhibit growth of side shoots
  • Inhibit leaf abscission (leaf fall)
26
Q

Plant hormones and their effects: (4)

Gibberellins

A

Promote:

  • Seed germination
  • Stem elgongation
  • Side shoot formation
  • Flowering
27
Q

Plant hormones and their effects: (2)

Ethene

A

Promotes:

  • Fruit rippening
  • Leaf abscission
28
Q

What are auxin and gibberellins described to be?

Give an example of each

A

Synergenic - They work together to have a really big effect

  • e.g. Work together to make the plant grow really tall

They can also sometimes be called antagonistic - Oppose each other’s action

  • e.g. Gibberellins stimulate growth of side shoots but auxine inhibit the growth of side shoots
29
Q

What are plant meristems?

A

Plant meristems = Regions of undifferentiated cells capable of mitosis

  • They’re the souce of new cells for plant growth

NOTE: They’re the stem cells equivalent in plants

30
Q

What is apical dominance?

A

Apical dominance = The apical bud (tip of the plant) grows more than the side shoots

31
Q

Auxin and apical dominance + how it happens

A

Apical dominance

  • In many plants, side shoots don’t grow if the main shoot is growing, this is because the apical bud (shoot tip) is dominant over the lateral buds that can grow into side shoots.
  • Energy is not used to grow side shoots so benefits plants
    • Allows plant to grow vertically faster to reach more light + prevents too many side shoots from developing which would make the leaves shade each other
  • If apical bud is cut off, low conc of auxin at tip, stimulates lateral buds to grow into side shoots
    • E.g. when plant or hedge is pruned
32
Q

Experimental evidence for the role of auxins in apical dominance

A
  • If apical bud (shoot tip) cut off and IAA is applied:
    • IAA is an example of auxin
    • Lateral buds don’t grow into side shoots
    • IAA replaces the natural auxin and inhibits lateral bud growth
  • If growing shoot is turned upside down:
    • Lateral buds grow into side shoots
    • Auxin is unable to diffuse to the lateral buds against gravity
  • If a ring of auxin transport inhibitor is applied below the apical bud
    • Lateral buds grow into side shoots
33
Q

Gibberellins + stem elongation

A
  • Most plants produce gibberellins to regulate stem elongation
  • When genetically dwarf plants are treated with gibberellic acid (GA) - stems elongate considerably
34
Q

Gibberellins + seed germination

A

When seeds absorbs water, the embryo releases gibberellins which trigger the production of amylase which can hydrolyse starch → glucose

35
Q

Abscisic acid (ABA) + leaf abscission (leaf fall)

A

ABA is a plant hormone that stimulates the production of ethene - ethene stimulated leaf fall

Production of ABA triggers:

  • Cells in the layer at the base of the petiole (leaf stalk) seperate from each other
  • A protective layer of cells with wax in their walls forms on each side of the abscission layer to prevent infection + water loss
  • Vascular tissue is sealed
  • Leaf is broken off by a mechanical force e.g. wind
36
Q

Commercial uses of Auxin (4)

A
  • Sprayed on to fruits to inhibit abscission
    • So that fruits can be harvested together when ripe
  • Sprayed on to flowers before pollination
    • To stimulate the development of seedless fruit
  • Stem or leaf cuttings are dipped into auxin “rooting powder
    • Root powder stimulates root development
  • Synthetic auxins can be used as selective herbicides to kill broad-leaved weeds in a cereal field
    • Weeds grow too rapidly to support themselves ∴ fall over and die
37
Q

Commercial uses of Ethene (3)

A
  • Speeds up fruit ripening in apples, tomatoes and bananas
    • Fruit is picked when unripe + transported when hard so less damage caused
  • Promote fruit drop in cotton, cherry and walnut
  • Promote female development in cucumbers
    • Reduces self-pollination which makes cucumbers bitter
38
Q

Commercial uses of gibberellins (5)

A
  • Delays senescence (ageing) in citrus fruits
    • Can be left longer before being picked ∴ extend their availability
  • Stimulates stem elongation in bunches of grapes
    • Each grape can grow larger
  • Stimulated stem elongation in sugar cane
    • More sugar can be stored
  • Stimulates germination of barely seeds
    • Amylase converts starch → maltose to be used in brewing
  • Promotes seed production in young plants e.g. Conifers