Download PLANT GROWTH REGULATION AND RESPONSE

PLANT RESPONSES
Syllabus links
3.5.2 Responses in the Flowering Plant
Growth regulation.
Stimulus and response
• A stimulus is
anything that causes
a reaction in an
organism or in any of
its parts
• A response is the
activity of a cell or
organism as a result
of a stimulus
The structures required for
response by organisms
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Chemical or hormonal (plants and animals)
Nerve and sense organ system (animals)
Growth, muscular and skeletal systems
A defence or immune system
Plants do not possess nervous systems but
depend on chemical co – ordination for their
responses – much slower!!
Plant responses involve growth and changes in
growth
Responses in flowering plants
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External factors
Light
Day length
Gravity
Temperature
Internal factors
• Plants produce a number
of chemicals called
growth regulators
• These are produced are
produced in the
meristematic regions of
the plant – root tip or
shoot tip
Syllabus links
3.5.2 Responses in the Flowering Plant
Tropisms: definition of the following:
"phototropism", "geotropism",
"thigmatropism", "hydrotropism", and
"chemotropism".
Examples of phototropism and
geotropism.
Tropisms
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“A tropism is a
change in the growth
of a plant in response
to an external
stimulus”
Phototropism
Geotropism
Thigmotropism
Chemotropism
Hydrotropism
Syllabus links
3.5.2 Responses in the Flowering Plant
Regulatory system: definition of a “growth
regulator”, transport through the vascular
system, combined effect, growth promoter
and growth inhibitor.
CIT: Use of plant regulators: any two
examples.
PA: Investigate the effect of I.A.A. growth
regulator on plant tissue.
Growth Regulators
• Plant responses are due to growth
regulators
• A growth regulator is a chemical that
controls the growth of a plants
• Regulator that promotes growth - Auxin
stimulates cell elongation
• Regulator that inhibits growth
• Ethene inhibits cell elongation
Growth Regulators
• They are active in very small amounts
• They are produced in the meristems
• They are transported in the xylem and
phloem
• Their effects are dependent on
concentration
• A small amount of growth regulator can
have great effect on growth
Auxins
Auxins cause:
– Stem growth
– Root growth
– Fruit formation ( at certain concentrations)
Example of Auxin = IAA Indoleacetic acid
Auxins
Production sites
• Apical Meristems
• Seed Embryos
• Young leaves
Functions of Auxins
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Stem elongation
Root growth
Cell differentiation
Development of fruit (IAA)
Apical dominance ( inhibit side branches)
Phototropism
Geotropism
Effects of auxins
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Tropisms
Apical dominance
Fruit formation
Root growth
Tropisms
Causes cell elongation and growth
or bending
Apical dominance
• Auxin produced in the apex (tip) will pass
down the stem and inhibit lateral buds
• This means that the apex will grow at the
expense of the lateral buds will grow at the
expense of the side branches
• Clearly seen in cacti and conifers
• If the apex is removed the side branches
are allowed to develop
• Produces low bushy forms in this case
Fruit formation
• IAA is made in
developing seeds which
stimulates food to form
in the fruit
• If IAA is artificially
applied to flowers before
pollination and
fertilisation occur, the
ovary enlarges and
forms seedless fruit –
parthenocarpic fruit
(virgin fruit)
• Examples include
seedless grapes,
oranges and tomatoes
Root growth
• At low concentrations,
IAA causes roots to
grow. IAA can be
applied artificially to
stimulate rooting
The mechanism of a plant
response to light (phototropism)
Growth Inhibitors
Ethene is a gas. It is produced in:
• Stem nodes
• Ripe fruits
• Decaying leaves
It causes:
• Fruits to ripen
• Leaves to fall in autumn
• Plants to age
Commercial Growth
Regulators
Ripen bananas
• Bananas are picked
green – ethene is
used to stimulate
ripening just before
distribution
Rooting Powders
• Contain synthetic
growth regulator NAA.
It stimulates rapid root
formation on stem
cuttings
Syllabus links
• 3.5.2 Responses in the Flowering Plant
Name four methods of anatomical or
chemical adaptation that protect plants.
Adaptations for Protection in
Plants
They protect themselves against:
– Loss of water
– Overheating
– Infection from micro organisms
– Being eaten by herbivores
Plant protection
Plants can adapt
themselves for
protection in two
ways:
– 1. Structural or
anatomical
adaptations
– 2. Chemical
adaptations
Structural Adaptations
• Bark/epidermis prevents entry of
microbes and reduces loss of water
• Thick cuticle on stem or leaves in plants
that live in dry places
• Thorns prevent plants from being eaten
by herbivores
• Stinging cell in epidermis prevent plants
been eaten
• Guard cells change shape when they lose
water which causes stomata to close and
this reduces water loss
Chemical Adaptations
• Production of Tannins to make the plant
indigestible
• Production of toxic chemicals to prevent
growth of insect larvae
• Production of strychnine and nicotine in
legumes that damage nerves and muscles
• Production of heat shock proteins to
protect enzymes when temperatures are
high