5.5.1: Plant responses to the environment Flashcards

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1
Q

What are the specific responses to the threat of herbivores that plants show? (chemical defenses)

A

Tannins
Alkaloids
Pheromones

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2
Q

What is the role of tannins?

A
  • Toxic to microorganisms and larger herbivores
  • In leaves, they are found in the upper epidermis and make the leaf taste bad.
  • In roots, they prevent infiltration by pathogenic microorganisms.
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3
Q

What are alkaloids derived from and what is their role?

A
  • Derived from amino acids.

- Feeding deterrent to animals as they taste bitter.

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4
Q

Where are alkaloids located?

A

In growing tips and flowers, and peripheral cell layers of stems and roots.

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5
Q

What are pheromones?

A

-Chemicals which are released by one individual and which can affect the behaviour or physiology of another.

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6
Q

What are tropisms?

A

Directional Shoot responses of plants.

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7
Q

What do tropisms include?

A
  • Phototropism
  • Geotropism
  • Chemotropism
  • Thigmotropism
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8
Q

Describe phototropism.

A
  • Shoots grow towards light (+vely phototrophic)

- Enables them to photosynthesise.

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9
Q

Describe geotropism.

A
  • Roots grow towards the pull of gravity.
  • Anchors them to the soil.
  • Helps them to take up water which is needed for 1.support (to keep cells turgid)
    2. Raw material for photosynthesis
    3. To help cool the plant.
  • Also minerals e.g. nitrates, needed for amino acid synthesis.
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10
Q

Describe chemotropism.

A

-On a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertilisation can take place.

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11
Q

Describe thigmotropism

A

Shoots of climbing plants, such as ivy, wind around other plants or solid structures to gain support.

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12
Q

What is a positive tropic response?

A

-If a plant responds towards a stimulus

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13
Q

What is a negative tropic response?

A

-If a plant responds away from a stimulus

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14
Q

What is a non-directional response to external stimuli called?

A

-Nastic responses

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15
Q

What is an example of thigmonasty?

A

-The sensitive plant, Mimosa pudica, responds to touch with a sudden folding of the leaves.

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16
Q

What ensures that hormones in plants only act upon the correct tissues?

A

-Specific hormones have specific shapes which can only bind to specific receptors with complimentary shapes on the membranes of the target cells.

17
Q

What is the effect of the hormone cytokines?

A
  • Promote cell division
  • Delay leaf senescence
  • Overcome apical dominance
  • Promote cell expansion
18
Q

What is the effect of the hormone Abscisic acid?

A
  • Inhibits seed germination and growth

- Causes stomatal closure when the plant is stressed by low water availability

19
Q

What is the effect of the hormone Auxins?

A
  • Promotes cell elongation
  • Inhibits growth of side shoots
  • Inhibits leaf abscission (leaf fall)
20
Q

What is the effect of the hormone Gibberellins?

A

-Promotes seed germination and growth of stems

21
Q

What is the effect of the hormone ethene?

A

-Promotes fruit ripening

22
Q

How do hormones move around a plant?

A
  • Active transport
  • Diffusion
  • Mass flow in the phloem sap or in xylem vessels.