Transcript Responses in Plants - Ms Curran`s Leaving Certificate Biology

Responses in Plants
Stimuli Plants respond to:
• Light
•Phototropism
• Gravity
•Geotropism
• Water
•Hydrotropism
• Chemicals
•Chemotropism
• Touch
•Thigmotropism
Tropisms
A Tropism is a change in the growth of a
plant in response to an eternal stimulus
• Negative tropism
– The growth is away from the stimulus
• Positive tropism
– The growth is towards the stimulus
Phototropism
http://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/tropisms.html
Geotropism
Responses in Plants
Plants respond by
• Changes in their pattern of growth
• Flowering
• Production of chemicals
External Factors Regulating
Growth
• Light Intensity
• Day Length
• Gravity
• Temperature
Internal Factors Regulating
Growth
• A series of chemicals called growth
regulators
• These chemicals are produced in
meristematic regions
Eg. Root tip and shoot tip
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
Objectives – What you will
need to know from this section
 Study auxin as an example of a plant growth
regulator under the headings of :
production
 initiator
 production site(s),
 function,
 different effects.
AUXINS -- HIGHER LEVEL
 Auxins affect virtually every aspect of plant development, and
how they respond to environmental stimuli.
 AUXINS influence includes
 phototropism,
 geotropism,
 cell enlargement and growth,
 apical dominance,
 root growth,
 fruit development,
 vascular development,
 and senescence [aging].
AUXINS
 Promote cell enlargement and growth
 Are involved in phototropism—stem bends towards
light.
 Are responsible for apical dominance, where the main
bud inhibits the growth of buds lower down stem.
 Regulate the differentiation of the vascular tissue
(xylem and phloem).
 Indole-3-acetic acid (IAA) is the most abundant
naturally-occurring auxin,
 IAA (Indoleacetic acid) is an auxin that is made in the
meristems of shoots, buds and root, and in the tips of
coleoptiles [of grasses].
 Auxin travels backwards
from the tip in the vascular
tissue and causes cells to
elongate (get longer).
 This makes the zone of
elongation grow and so the
tip is pushed further
upwards (in shoots) and
downwards (in roots).
 Movement is by active
transport from cell to cell –
this requires energy.
Auxins
 promote cell enlargement and growth,
 are involved in phototropism and apical dominance
PHOTOTROPISM
APICAL
DOMINANCE
 A tropism is a plant’s response to a stimulus
coming from one direction, e.g. sunlight, gravity.
 Phototropism is a
growth response of
a stem towards
light, so that it can
receive the
maximum amount
of light for
photosynthesis.
APICAL
DOMINANCE
 Auxins are
responsible for
apical dominance,
where the main bud
inhibits the growth
of buds lower down
stem.
 This photograph
shows side buds
sprouting when the
main stem is cut off
[pruned].
In shoots, light causes auxin to move down the shaded part of the stem, causing
the shoot to grow towards the sunlight. This is called PHOTOTROPISM.
Quicker growth here
due to more hormones
Artificial auxins can also be used to kill weeds, stimulate root
formation in cuttings, …
Uses of plant regulators
Artificial auxins are used in rooting
powders to stimulate root formation in
stem cuttings.
A synthetic auxin [2,4-D] is used as a
selective weedkiller, making the plants
grow too fast.
Fruit is transported green and
unripe, and can then be
quickly ripened by spraying it
with ethene.
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
Adaptations for Protection in
Plants
Plants need to protect themselves
from their environment
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 of 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
Most important adaptation
Plants can grow and regenerate
throughout their life.
They can produce new roots, stems,
leaves.