Transcript BEHAVIOURAL ADAPTATIONS PLANTS

BEHAVIOURAL
ADAPTATIONS
Behaviour in Plants
(Or is it physiological)
Plant Behaviour
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What stimuli impact on plants and how do
plants respond as a result?
– The
effect of environmental
stimuli on plants and their effect
on plant growth
– Rhythmic activities of plants in
response to external stimuli
TROPISMS
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External factors, such as light, gravity and touch, exert an
influence on plant growth and development.
The growth of a plant in response to a stimulus such as
light or water is called a tropism
When a plant grows towards a stimulus, it is termed a
positive tropism
When a plant grows away from a stimulus, it is termed a
negative tropism
TROPISMS
Light as a stimulus
When a plant moves in response to light, it shows
phototropism
Movement towards the light is a –
Positive phototropism
TROPISMS
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Investigations by Charles Darwin which had covered and
uncovered growth tips of plants showed the tip had an
influence that passed from the tip to the area where
bending occurred
Auxin – a plant hormone is produced in the tip of a
coleoptile and causes growth of cells in the coleoptile.
The tip is the site of reception of the light stimulus.
The growing region below the tip is the effector
TROPISMS
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Auxin moves away from light
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Auxin influences the growth rate of plant cells. More auxin,
increased growth rate.
When a seedling is evenly illuminated, auxin is evenly
distributed throughout the growth tip.
When light is concentrated on one side of the plant, auxin
moves away from the light, to the darker side of the tip
Increased concentration of auxin in one side of the plant
results in accelerated growth (elongated growth) of the cells on
that side.
The uneven growth of cells results in bending of the plant.
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TROPISMS
Gravity as a stimulus
Auxin stimulates the growth of cells in shoots but inhibits
the rate of growth in the cells of roots.
Lie a seed on its side and the auxin settles in the lower
part of the shoot and the roots due to gravity
Which way will the roots go?
Which way will the shoots go?
TROPISMS
Gravity as a stimulus
In a horizontal seedling, auxin accumulates (settles) along
the lower horizontal part of the shoot (due to gravity)
causing the cells in that part to grow faster
Hence, the shoot turns up away from gravity
In the roots, it is the upper part that grows faster so that
the root turns downwards towards gravity. Auxin slows
the cell growth in the roots
Geotropism is the plant responding to gravity
TROPISMS
Gravity as a stimulus
Shoots show negative geotropism
Roots show positive geotropism
The response of plants to distribution of auxins allows plants to
orient themselves to a more favourable position within their
environment
How do tropisms assist the plant in photosynthesis?
CLIMBING PLANTS
Thigmotropism is the change in growth
because of contact with another object.
Explain what would be happening in regard
to the distribution of auxin in a climbing
plant when it comes in contact with another
object. How does auxin contribute to
thigmotropism?
RHYTHMIC ACTIVITIES
• Plants, like animals exhibit a range of
rhythmic behaviours.
RHYTHMIC ACTIVITIES
Time as a stimulus
Biological clock – the internal clock or timing
system for sleep patterns. The sleep pattern
occurs every 24 hours
An activity that follows a 24 hour cycle is called a
Circadian Rhythm (or circadian cycle)
Plant behaviours that follow a circadian rhythm –
opening and closing of flowers, nectar and
perfume production
This movement is independent of the direction of the
stimulus – Nastic Movement.
RHYTHMIC ACTIVITIES
Solar Tracking or Heliotropism
Leaves and flowers that are able to move
during the day so they are oriented either
perpendicular or parallel to the sun’s direct
rays.
Eg. Sunflowers
How can heliotropism as a behaviour assist
in survival?
RHYTHMIC ACTIVITIES
Photoperiodism
Timing of Flowering
The relative length of day and night is the
photoperiod
The response of plants to particular
periods of light and dark is called
photoperiodism.
The length of day and night to which a
plant is exposed is very important.
RHYTHMIC ACTIVITIES
Photoperiodism
Photoperiodism differs between plants
Short day plants – eg Chrysanthemums flower
only when the day length is shorter than some
critical period.
Long day plants – eg Carnations flower only
when day lengths are longer than certain critical
minimum.
Day neutral plants – eg Dandelion flower
regardless of the length of the day.
RHYTHMIC ACTIVITIES
Photoperiodism
How would classify plants that flower in
the spring?
Although the terms short-day and long-day
plants suggests the exposure to light is
critical. The length of darkness is also
very critical.
RHYTHMIC ACTIVITIES
Photoperiodism
Example – Cocklebur (short-day plant) would only
flower when the dark period exceeded nine
hours; the day length does not matter.
When the cocklebur is exposed to even a brief
flash of light during the dark period, the plant no
longer flowers.
Uninterrupted dark is important for flowering
Short-day plants are really long-night plants.
Long-day plants are really short-night plants.
RHYTHMIC ACTIVITIES
Photoperiodism
Phytochromes, light sensitive pigments in
leaves react to a photoperiod that is appropriate
for the particular plant.
As a result, the leaves produce a hormone
This hormone then travels to buds which then
flower
Photoperiod can also be important in breaking
the dormancy of seeds and other parts of plants.