Tropisms and Growth

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Tropisms and Growth

• Accelerated Biology

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Tropisms

• Stimulus an environmental condition that causes
  a plant response
• Tropism growth of plant in a certain way in
  response to a stimulus

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Phototropism

• Phototropism growth toward () or away from ()
  light
• Plant shoots display positive phototropism
• Plant roots display negative phototropism

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Gravitropism

• Gravitropism growth toward () or away from ()
  gravity
• plant shoots display negative gravitropism
• Plant roots display positive gravitropism
• seedling shoot grows upwards and roots grow
  downwards, no matter how seed landed!

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Thigmotropism

• Thigmotropism response to physical contact
• plant shoots can coil or grasp and use objects
  for support while growing toward light
• Ex) morning glories, clematis
• this is also how the Venus fly trap closes

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Plant Hormones

• Auxin a plant hormone that causes cell walls to
  become more flexible which allows cells to
  elongate as they grow
• Auxin accumulates on the dark side of the plant
• cells on the dark side elongate more than cells
  on the light side
• causes stem to grow towards the light

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Plant Growth

• Meristems a region of undifferentiated plant
  cells that are capable of dividing and developing
  into specialized plant tissue

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Plant Growth

• Primary Growth
• Apical meristems located at the tips of the
  stems and roots
• stems and roots become longer, without becoming
  wider
• like stacking plates one on top of another, the
  pile will only get taller, but never wider

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Plant Growth

• Secondary Growth
• most dramatic in woody plants
• occurs in two meristems
• cork cambium produces cork cells
• vascular cambium produces vascular tissue
• stem grows in diameter
• result annual rings

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Plant Growth

• What will this carving look like 50 years from
  now?
• Discuss with your partner.