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Plant

Hormones

and

Adaptations – V2

Slide # 16

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Hormone Action on Plants

Hormone-producing

cells

Target

cells

Movement

of hormone

  1. Plant cells can produce hormones. Hormones are chemicals that travel throughout the plant causing target cells to respond.
  2. In plants, hormones control:
    1. Plant growth and development
    2. Plant responses to environment

Cells in one blooming flower signal other blooms to open using hormones.

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Plant cells send hormone signals to tell each other:

  1. When to drop their leaves.
  2. When to start new growth.
  3. When to cause fruit to ripen.
  4. When to cause flowers to bloom.
  5. When to cause seeds to sprout.

Leaf Drop

Fruit

Ripening

Sprouting

Corn Seeds

Cactus

Blooming

Tree Budding

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There are 4 major classes of hormones:

  1. Gibberellins
  2. Cytokinins
  3. Abscisic Acid (ABA)
  4. Ethylene

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1. Gibberellins�

  • Gibberellins promote embryo growth in the seed.
  • They promote development of vascular tissue.
  • Gibberellins also promote stem growth.

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2. Cytokinins�

  • Cytokinins promote cell division and cell differentiation in growing plants.
  • They also delay the aging of fruit and leaves.

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3. Ethylene

  1. Fruit tissues release a small amount of ethylene.
  2. Causes fruits to ripen.
  3. As fruit becomes ripe, it produces more and more ethylene, accelerating the ripening process.

Ethylene released by apples and tomatoes causes fruit to age quickly.

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4. Abscisic Acid (ABA)�

  • Is a growth inhibitor and is mainly manufactured in mature leaves.
  • ABA blocks growth hormones and inhibits the growth of:
    • germinating seeds
    • growth of buds
    • plant stems

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Plant Hormone Summary

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Adaptations: Plant Tropisms

1. Tropism: the way a plant grows in response to stimuli in the environment.

    • Phototropism: growth response to light

-Plants bend towards light

b. Geotrophism: growth response to gravity

-plant roots grow down with gravity, shoots (stems) grow up against gravity and out of the soil.

c. Thigmotropism: growth response to touch

-vines grow up around trees, Venus flytrap closes when leaves are touched

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Guess the type of tropism shown:

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Geotropism

Thigmotrophism

Geotropism

Phototropism

Phototropism