chemical coordination in plants · the growth response of a plant to a directional stimulus is...
TRANSCRIPT
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CHEMICAL COORDINATION IN PLANTS
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CHEMICAL COORDINATION IN PLANTS
Like humans, plants respond to a stimulus
Their movements are slower
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TYPES OF RESPONSES
Tropisms
Day length
Temperature
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TROPISMS
Plants respond involves changing rate of growth
Two stimuli act on the plant
Direction of light
gravity
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TROPISM
Light (phototropism) and gravity (geotropism)
are directional stimuli. They act in a particular
direction
The growth response of a plant to a directional
stimulus is tropisms
Phototropism Geotropism
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TROPISM
Growth can be positive – toward the stimulus
or negative – away from the stimulus
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TROPISM
Plant growth
Stems exhibit positive phototropism while most roots
exhibit negative phototropism.
Roots exhibit positive geotropism while stems and
leaves exhibit negative geotropism
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TROPISM
Why do aerial part of the plant respond in a
positive phototropism?
Why do roots of a plant respond in a positive
geotropism?
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TROPISM
Some plant roots show a positive hydrotropism
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WHAT WILL HAPPEN
Hole for light
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Complete questions 9 & 10
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DETECTING THE STIMULUS
Since plants do not have a nervous system,
hormones are used to detect the stimulus
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PLANT HORMONES (PLANT GROWTH
SUBSTANCES)
Auxin
Cytokinin
Gibberillin
Abscisic acid
Ethylene
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AUXIN – PLANT GROWTH REGULATORS
Location: seed embryo; buds and young
leaves
Function: stem elongation; root growth,
differentiation, branching; fruit
development; apical dominance; tropisms
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CYTOKININS
Location: roots (and actively growing
tissues)
Function: root growth and differentiation;
cell division and growth; germination;
delay senescence (aging)
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GIBBERELLINS
Location: meristems of apical buds and
roots, young leaves, embryo
Function:germination of seed and bud;
stem elongation; leaf growth; flowering;
fruit development; root growth and
differentiation
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ABSCISIC ACID
Location: leaves, stems, roots, green fruit
Function: inhibits growth; closes stomata
during stress
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ETHYLENE
Location: ripening fruit tissue; stem nodes;
aging leaves and flowers
Function:fruit ripening; promotes/inhibits:
growth/development of roots, leaves, and
flowers
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DETECTING THE STIMULUS
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DAILY AND SEASONAL RESPONSES
Photoperiodism - a plants response to light
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DAILY AND SEASONAL RESPONSES
Short-day plant: light period shorter than a critical length
to flower (flower in late summer, fall, or winter; poinsettias,
chrysanthemums)
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DAILY AND SEASONAL RESPONSES
Long-day plant: light period longer than a critical length to
flower (flower in late spring or early summer; spinach,
radish, lettuce, iris)
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DAILY AND SEASONAL RESPONSES
Day-neutral plant: unaffected by photoperiod (tomatoes,
rice, dandelions)
Critical night length controls flowering
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CLINOSTATS
Used to eliminate any directional stimulus that
may act on the seed
A clinostat only produces the effect of
weightlessness along its axis of rotation
Explain what will happen to the roots
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EXPERIMENTS
Read Experiment 14 on page 140 and complete
questions on your sheet