Plant%20Responses%20and%20Adaptations

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Plant Responses and Adaptations

• Chapter 25 Biology II

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Plant Hormones

• Chemical substances that control
• A plants patterns of growth and development
• A plants responses to environmental conditions
• Target Cell cell affected by a particular hormone

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Auxins

• Stimulate cell elongation
• Produced in the apical meristem
• Transported downward into the rest of the plant
• Responsible for phototropism and gravitropism

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Auxins Phototropism

• Tendency of plants to grow toward a source of
  light

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Auxins Gravitropism

• Tendency of a plant to grow in a direction in
  response to the force of gravity

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Auxins

• Lateral Bud meristematic area on the side of a
  stem that gives rise to side branches
• Apical Dominance phenomenon in which the closer
  a bud is to the stems tip, the more its growth
  is inhibited
• Herbicide auxin-like weed killers compound that
  is toxic to plants

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Cytokinins

• Plant hormones that are produced in growing roots
  and in developing fruits and seeds
• Stimulate cell division and the growth of lateral
  buds
• Cause dormant seeds to sprout

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Gibberellins

• Growth-promoting substance produced by plants
• Causes dramatic increases in size, particularly
  in stems and fruits
• Produced by seed tissue
• Responsible for the rapid early growth of many
  plants

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Ethylene

• Plant hormone that
  stimulates fruits to ripen
• Released in small amounts
  as a response to auxins
• Commercial products can use this to control the
  ripening process treated with synthetic ethylene

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Tropisms

• The response of plants to environmental stimuli
• Gravitropism
• Phototropism
• Thigmotropism

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Thigmotropism

• Response of plants to touch
• Examples
• A plant that is touched regularly may be stunted
  in its growth-sometimes quite dramatically
• Vines and climbing plants-tips wrap around objects

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Rapid Responses

• Some responses do not involve growth they are
  not tropisms
• Examples
• Mimosa pudica the sensitive plant
• The Venus flytrap

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Photoperiodism

• Responsible for the timing of seasonal activities
  such as flowering and growth
• Phytochrome plant pigment responsible for
  photoperiodism

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Short-Day Plants

• Plants that flower when daylight is short
• Also called long-night plants

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Long-Day Plants

• Plants that flower when days are long
• Also called short-night plants

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Winter Dormancy

• Period of time during which a plant embryo is
  alive but not growing
• As cold weather approaches, deciduous plants
• Turn off photosynthetic pathways
• Transport materials from leaves to roots
• Seal leaves off from the rest of the plant

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Abscission Layer

• Layer of cells at the petiole that seals off a
  leaf from the vascular system

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Aquatic Plants

• To take in sufficient oxygen, many aquatic plants
  have tissues with large air-filled spaces through
  which oxygen can diffuse

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Salt-Tolerant Plants

• Leaves have specialized cells that pump salt out
  of the plant tissues and onto the leaf surfaces
• Example mangroves

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Desert Plants

• Also called xerophytes
• Extensive roots
• Reduced leaves
• Thick stems that can store water

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Nutritional Specialists

• Plants that have specialized features for
  obtaining nutrients
• Carnivorous plants obtain nutrients from
  digested prey
• Parasites plants that extract water and
  nutrients directly from a host plant
• The dodder plant Cuscuta

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Epiphytes

• Plants that grow directly on the bodies of other
  plants
• Gather their own moisture and produce their own
  food, unlike parasitic plants
• Spanish moss-not a moss, but a bromeliad!

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Chemical Defenses

• Many plants defend themselves against insect
  attack by manufacturing compounds that have
  powerful effects on animals