Transcript plant_coordination_amp_response

MAKING SENSE OF
TROPISMS
IGCSE Biology
3.3 Chemical Coordination in Plants
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• Do you understand that plants respond
to stimuli?
• Can you give an example of positive
phototropism?
• How do plant roots and stems respond to
gravity?
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• Its not any animals that can respond to their
environments.
Click on the images to watch the video about each plant
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• A growth response of a plant to directional
stimuli is called a tropism.
• Grows towards stimuli – POSITIVE
• Grows away from stimuli – NEGATIVE
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A tropism where the stimuli is
light is called phototropism.
WHY?
• The shoot of a plant grows
towards the light to maximise
photosynthesis.
• Called positive phototropism.
Positive Phototropism
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• If there is no light under the soil, how does a
germinating seed know which way to grow?
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A tropism where the stimuli is
gravity is called geotropism.
WHY?
• The root of a plant grows towards gravity to
uptake water & mineral ions
• Called positive geotropism.
Positive Geotropism
POSITIVE PHOTOTROPISM
Stems grow upwards
NEGATIVE GEOTROPISM
Stems grow upwards
NEGATIVE PHOTOTROPISM
Roots grow downwards
POSITIVE GEOTROPISM
Roots grow downwards
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• AUXIN = growth hormone produced by plants
PRODUCED AT:
Tip of the shoot – diffuse downwards
ROLE OF AUXIN:
It causes cell elongation & division.
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1.
Auxin is
produced at
the tip of the
shoot and
causes it to
grow.
2.
3.
Auxin diffuses
AWAY from the light
into the shadowed
side
The shaded side
elongates faster
than the
illuminated side
and the shoot
bends towards
the light