Transcript Plant behaviour

Plant behaviour
Plant BEHAVIOUR?!
 Plants are also influenced by external
factors/stimuli.
 Behaviour = reaction to stimulus
Tropisms
 The growth of a plant in response to a
stimulus
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Light
Water
Gravity
Touch
Light tropism
 Also called PHOTOTROPISM
 Plants will face the light, usually
sunlight
 If plant FACES light, it is a POSITIVE
phototropism. If it turns away from
the light, it is a NEGATIVE
phototropism
Phototropism experiments
 Tips of growing grass were covered
 Tips no longer bent toward light
 Therefore, region of receiving light
messages must be in the tip
 We now know that AUXIN, a plant
hormone, is produced in the plant tip,
and creates new cells for growth of
the tip
Auxin moves away from light
 If the plant is bathed in even light,
there is an even amount of auxin
throughout the entire tip.
 If the light is concentrated on one
side, the auxin moves to the “dark
side”, and produces greater growth
on that side, elongating one side of
the tip, creating a bend.
The action of auxin
Gravity tropism
 Geotropism
 Roots head down into the ground,
while the tip of the plant grows
upwards
 Again – auxin is the culprit!
Why have a geotropism?
 Gain sunlight through green parts
• Gain water through root system from
ground water
Climbing plants
 Thigmotropism – change in growth in
response to contact with another
object
 Twisting comes from elongation of
cells that are not touching the object
 Where do you think auxin is
concentrated?
Rhythmic behaviours in plants
 Rhythmic behaviours: behaviours that
happen daily, seasonally, yearly
 Time stimulus
 Solar tracking
Time as stimulus for rhythmic
behaviour
 Plants have a biological clock
 Leaves horizontal in day, “sleep” at
night (why?)
 24 hour cycle – circadian rhythm
 Opening and closing of flowers is also
circadian
Solar tracking
 Heliotropism
 Leaves and flowers move throughout
the day so they are facing sun
 Eg. Sunflowers (Helianthus annuus)
have the ability to face the sun all
day. What is the benefit of this?
Timing of flowering
 Photoperiodism – response of plants to
different periods of light (relative length of
day and night)
 Some plants (eg. Chrysanthemum) only
flower when day is shorter than night –
short-day plants.
 Some (eg. Carnations) only flower when
day is longer than night – long-day plants
 If they flower regardless of day/night
length (eg. Dandelions), they are dayneutral plants
Short and long day plants
 If the “dark” period
is interrupted:
 Short-day: no
flowering
 Long-day: will flower
Short and long day plants
 During light hours, hormones are
produced
 These influence flower growth
 The right amount of hormone must
be produced for the specific plant
Activities
Glossary: tropism, phototropism, auxin,
geotropism, thigmotropism, biological
clock, circadian rhythm, heliotropism,
photoperiodism, short-day plant, long-day
plant, day-neutral plant
Quick Check Questions: pg 367
Biochallenge pg 368, Chapter Review Q 2, 3,
4, 5, 6, 7, 8, 9, 10.