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AP Biology
February 15, 2012
Objective Describe the effects of various
hormones on plant growth Investigate how a plant respond to
different stressors
Homework Hormones Free Response Essay
AP Biology
The Discovery of Plant Hormones Any response resulting in curvature of organs
toward or away from a stimulus is called a tropism
In the late 1800s, Charles Darwin and his son Francis conducted experiments on phototropism, a plant’s response to light
They observed that a grass seedling could bend toward light only if the tip of the coleoptile was present
Phototropism
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AP Biology
They postulated that a signal was transmitted from the tip to the elongating region
In 1913, Peter Boysen-Jensen demonstrated that the signal was a mobile chemical substance
How would they design their experiments to test these hypothesis?
© 2011 Pearson Education, Inc.
AP Biology
Figure 39.5
Control
Light
Shaded side
Illuminatedside
Boysen-Jensen
Light
Light
Darwin and Darwin
Gelatin(permeable)
Mica(impermeable)
Tipremoved
Opaquecap
Trans-parentcap
Opaqueshield overcurvature
RESULTS
AP Biology
In 1926, Frits Went extracted the chemical messenger for phototropism, auxin, by modifying earlier experiments
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AP Biology
Plant hormones Auxin cytokinins gibberellins abscisic acid ethylene and more…
AP Biology
Auxin (IAA) Effects
controls cell division & differentiation
phototropism growth towards light asymmetrical distribution of auxin cells on darker side elongate faster
than cells on brighter side apical dominance
AP Biology
Cytokinins Cytokinins are so named
because they stimulate cytokinesis (cell division)
Control of Cell Division and Differentiation
Cytokinins are produced in actively growing tissues such as roots, embryos, and fruits
Cytokinins work together with auxin to control cell division and differentiation
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AP Biology
Gibberellins Family of hormones
over 100 different gibberellins identified
Effects stem elongation fruit growth seed germination
plump grapes in grocery stores have been treated with gibberellin hormones while on the vine
AP Biology
Abscisic acid (ABA) Effects
Closure of stomata during H2O crisis slows growth seed dormancy
high concentrations of abscisic acid germination only after ABA is inactivated or
leeched out
survival value: seed will germinate only under optimal conditions
light, temperature, moisture
AP Biology
Ethylene Hormone gas released by plant cells Effects
fruit ripening leaf drop
Senescence (cell death) Abscission (drop)
One bad apple spoils the
whole bunch…
AP Biology
Fruit ripening Adaptation
hard, tart fruit protects developing seed from herbivores
ripe, sweet, soft fruit attracts animals to disperse seed
Mechanism triggers ripening process
breakdown of cell wall softening
conversion of starch to sugar sweetening
positive feedback system ethylene triggers ripening ripening stimulates more ethylene production
AP Biology
Etylene Develop a hypothesis about what will
happen to the bananas in the bags
Be sure to explain why you think it will happen that way.
AP Biology
Apoptosis in plantsWhat is the evolutionary advantage of loss of leaves in autumn?
Many events in plants involve apoptosis response to hormones
ethylene auxin
death of annual plant after flowering senescence
differentiation of xylem vessels loss of cytoplasm
shedding of autumn leaves
AP Biology
Learning Check Identify the function and location of the
following plant hormones Auxin Cytokinins Gibberellins Abscisic acid Ethylene
AP Biology
Plant Stress Stress response You will be divided into groups. Each group will
research and explain how one of the following 1) causes stress to the plant, 2) effects a plants growth, and 3) how the plant over comes the stress
Gravity Herbivory Light Salt Drought Mechanical stimuili Flooding Heat Cold Disease
AP Biology 2007-2008
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