Chapter 25 Plant Responses and Adaptations.

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Chapter 25 Plant Responses and Adaptations.
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What is a tropism?

• Tropism a response of a plant to an
  environmental stimulus.

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What is phototropism?

• Phototropism a tendency of plants to grow
  toward a source of light.

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What is thigmotropism?

• Thigmotropism the response of plants to touch.

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What is gravitropism?

• Gravitropism a tendency of a plant to grow in a
  direction in response to the force of gravity.

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How do cytokinins affect plant growth?

• Stimulate cell division and growth of lateral
  buds
• Cause dormant to sprout
• Delay aging of leaves
• Inhibit elongation and cause cells to grow thicker

As a result of cytokinin the top carrot is 2x
bigger than the other.
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How do gibberellins affect plant growth?

• Produce increase in size in stem and fruit
• Responsible for rapid early growth in many plants

Notice the difference in sizes of the fruit
bunches and plants
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How does ethylene gas affect plants and how is it
used on a fruit?

• Trees suffer leaf loss
• Ethylene stimulates fruits to ripen
• Use to treat fruit picked before ripening to
  ripen them when being handled for shipment

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The above diagram shows how auxin production in
a plant causes it to grow toward sunlight.
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How does auxin affect plant growth in presence of
light?

• Light hits one side of stem
• Higher concentration of auxins develops in the
  shaded part of the stem
• Change in concentration stimulates cells in the
  dark side to elongate
• Result the stem bends away from the shaded side
  and toward the light

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How does auxin affect plant growth in the
presence of gravity?

• Built up on the lower sides of roots and stems
• In roots auxin inhibit cell growth and elongation
  
• Result roots grow downward

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How does auxin affect plant height or width?

• As a stem grows in length, it produces lateral
  buds
• Lateral bud gives rise to side branches on the
  side of stem
• Growth at lateral buds is inhibit by auxin,
  which is on the stems tip
• The closer a lateral bud is to stems tip, the
  more is it inhibited

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Photoperiodism

• What Is Photoperiodism?
• Photoperiodism is the response of plants to
  periods of light and darkness.

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Short-day plants

• Plants such as chrysanthemums and poinsettias
  flower when days are short.

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Long Day Plants

• Pants such as spinach and irises flower when
  days are long.

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Phytochrome

• It is a plant pigment that is held responsible
  for photoperiodism.
• Absorbs red light
• Activates a number of signaling pathways within
  plant cells

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Tradescantia- A plant that shows growth response
to gravity upward when young and downward when
older.
Notice how the trunk of the tree to the right is
grow up away from gravity.
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Desert Plants Survival

• Some examples of desert plants are
• Cacti
• Ocotillos
• Lechugillas

• Have extensive roots, reduced leaves, and thick
  stems to help them survive.

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Lechugilla
Cacti
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Carnivorous Plants

• Live in bogs and wet or acidic places
• Trap food using special leaves

• Some examples of carnivorous plants are
• Pitcher plants
• Venus flytrap
• Sundews
• Butterworts

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Sundew
Pitcher Plants
Venus Flytrap
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Parasitic Plants

• These plants harm their host organisms
• Sometimes a threat to other species
• The dodder plant is a parasitic plant
• It has no chlorophyll and does not produce its
  own food
• It grows directly into the vascular tissue of its
  host
• Mistletoe grows as a parasite on many plants
  including conifers.

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Mistletoe Growing on a tree.
Dodder Plant (Cuscuta)
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Epiphyte Plants

• Epiphyte are plants that grow directly on bodies
  of other plants but cause no harm to the host
  plant.
• These plants carry out photosynthesis.
• A common epiphyte is Spanish moss.
• This plant is not moss, but is amember of
  bromeliad family
• Many orchids are epiphytes as well
• These grow on surfaces of other plants

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Spanish moss Hanging on a tree
Orchids In a tree
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Aquatic plants

• have tissues with large air filled spaces
• oxygen diffuses through these tissues
• have floating seeds that delay germination
• grow quickly after germination
• growing shoot extends above water surface
• EX bald cypress trees
• bladder warts
• water lettuce

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Water Lettuce
Bald Cypress Tree
Water lily
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Salt Tolerant Plant

• roots are adapted for harmful salt
  concentrations
• salt would normally kill the root hairs
• contain cells that pump water out of plant
  tissues
• water is pumped onto the leaf surfaces
• water on the leaves is washed off by rain
• EX Mangroves
• Shadescale
• Saltbrush

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Cropomea
Celosia
Opomea
Salt Tolerant Plants
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Some Plants Use Chemicals for Protection

• Act as a toxin to kill predator
• Example nicotine in tobacco plants will kill
  some insects and animals when ingested.
• Some plant chemicals repel predators
• Example- Milkweed tastes bad to some birds and
  insects.