Prentice Hall Biology

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Section 25-1

• 251 Hormones and Plant Growth
• A. Patterns of Plant Growth - meristems are the
  source of plant growth. Plants never stop
  growing.
• Plant Hormones - are chemical substances that
  controls a plants patterns of growth and
  development, and the plants responses to
  environmental conditions
• The four main hormones are
• Auxins
• Cytokinins
• Gibberellins
• Ethylene

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Figure 25-2 Hormone Action on Plants
Section 25-1
Hormone Action in Plants   -Plant hormones are
chemical substances that control patterns of
development as well as plant responses to the
environment. - Hormones are produced in one part
of the plant to control another part of the plant.
The cells affected by a hormone must have a
hormone receptor
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Section Outline
Section 25-1

• 251 Hormones and Plant Growth - Continued
• C. Auxins - are produced in the apical meristem
  and are transported downward into the rest of the
  plant. They stimulate cell elongation.
• D. Cytokinins - stimulate cell division and the
  growth of lateral buds, and cause dormant seed to
  sprout
• E. Gibberellins - produce dramatic increase in
  size, particularly in stems and fruit
• F. Ethylene - stimulates fruit to ripen

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Figure 253  Auxins and Phototropism
Section 25-1
Highconcentrationof auxin
Lowconcentrationof auxin
Control
Tipremoved
Opaquecap
Clearcap
Opaque shiedover base
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Figure 255 Apical Dominance
Section 25-1
Apical meristem
Lateral buds
Auxins produced in the apical meristeminhibit
the growth of lateral buds.
Apical meristem removed
Without the inhibiting effect of auxinsfrom the
apicial meristem, lateral budsproduce many
branches.
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Section Outline
Section 25-2

• 252 Plant Responses
• A. Tropisms - A plants ability to respond to
  external stimuli.
• Gravitropism - a plants response to the force of
  gravity. Controlled by auxins
• Phototropism - the tendency of a plant to grow
  toward a source of light. Auxins stimulate the
  elongation of stem cells on the dark side to
  elongate and the plant bends toward the light
• Thigmotropism - a plants response to touch. Vines
  and climbing plants like grapes have tendrils
  that wrap tightly around objects they encounter
• B. Rapid Responses - movement occurs from rapid
  changes in osmotic pressure. An example of a
  rapid change is the closing of a Venus fly trap
  leaf to capture a insect.

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Tropisms
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Section Outline
Section 25-2

• 252 Plant Responses - continued
• C. Photoperiodism - is responsible for the timing
  of seasonal activities such as flowering and
  growth.
• D. Winter Dormancy - as cold weather approaches,
  deciduous plants turn off photosynthetic
  pathways, transport materials from leaves to
  roots, and seal leaves off from the rest of the
  plant.
• 1. Leaf Abscission - photosynthesis stops and the
  green pigments are destroyed revealing the other
  colors that were there all along. Most water and
  available nutrients are removed from the leaf,
  and an abscission layer forms at the base of the
  leaf.
• 2. Overwintering of Meristems - produce thick
  waxy scales over the new leaf buds for the next
  spring. Xylem and phloem tissues pump themselves
  full of ions and organic compounds to act as an
  antifreeze during the cold winter.

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Photoperiodism and Flowering
Section 25-2
Long-Day Plant
Short-Day Plant
Midnight
Noon Long Day
Midnight
Noon Short Day
Midnight
Noon Interrupted Night
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Section Outline
Section 25-3

• 253 Plant Adaptations
• A. Aquatic Plants - to take in sufficient oxygen,
  many aquatic plants have tissues with large air
  filled spaces through which oxygen can diffuse.
  Other adaptations include seeds that float and
  quick growth following germination to allow the
  shoot to reach the surface of the water.
• B. Salt-Tolerant Plants - take in more salt than
  the plant can use to allow the roots to still
  absorb water by osmosis. The roots have adapted
  to tolerate the salt conditions that would
  destroy most plants. Excess salt is pumped out
  of the plant onto the leaves where it is washed
  away by the rain.
• C. Desert Plants - adaptations to a desert
  climate include extensive roots, reduces leaves,
  and thick stems that can store water. The spines
  on a cactus are actually modified leaves. Many
  seeds of desert plants can remain dormant for
  years.

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Plant Adaptations
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Section Outline
Section 25-3

• 253 Plant Adaptations - continued
• D. Nutritional Specialists - have specialized
  features for obtaining nutrients.
• 1. Carnivorous Plants - many live in bogs where
  there is little or no nitrogen present in the
  soil. Plants that live in these type of
  ecosystems have specialized leaves to capture and
  digest insects for a source of nitrogen. Ex)
  Venus fly trap and picture plant
• 2. Parasites - plants that extract water and
  nutrients directly from a host plant.
• E. Epiphytes - plants that are not rooted in the
  soil but instead grow directly on the bodies of
  other plants. Epiphytes are not parasites they
  gather their own moisture and produce their own
  food.
• F. Chemical Defenses - many plants defend
  themselves against insect attack by manufacturing
  compounds that have powerful affects on animals

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Compare/Contrast Table
Section 25-3
Comparing Carnivorous Plants, Epiphytes, and
Parasites
Characteristics Environment Method of obtaining
nutrients Examples
Carnivorous Plants bog leaves that trap and
digest insects pitcher plant, sundew, Venus
flytrap
Epiphytes host plant gather moisture from
rainfall and produce their own food Spanish moss,
orchid
Parasites host plant extract moisture and
nutrients from host plant dodder, mistletoe
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