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Chapter 25
Plant Responses
and Adaptations.
Set Up Foldable
• Fold Long and Skinny (hotdog)
• Fold short and fat 2 times (hamburger)
• Open so looks like below, crease is on top
What is a tropism?
Tropism ~ a response of a
plant to an environmental
stimulus.
Tropism
• Tropism is growth in response to an
external stimulus (factor that elicits a
response).
• Positive tropism: Plant growth toward a
stimulus (water, sunlight)
• Negative tropism: Plant growth away
from a stimulus (spilled gas, toxins, too
much sun or not enough)
What is phototropism?
Phototropism ~ a tendency of
plants to grow toward a
source of light.
Phototropism
• Phototropism is a
change in the growth of
a plant in response to
light.
• The stalk displays
positive phototropism
growing towards the
light.
What is gravitropism?
Gravitropism ~ a tendency of
a plant to grow in a direction
in response to the force of
gravity.
What is thigmotropism?
Thigmotropism ~ the
response of plants to touch.
Geotropism (Gravitropism)
• Geotropism is a change in
the growth of a plant in
response to gravity.
• The stalk displays a
negative geotropism
growing away from gravity.
• The roots display a positive
geotropism growing
towards gravity.
Hydrotropism
• Hydrotropism is a
change in the growth of
a plant in response to
water.
• The roots display a
positive hydrotropism
growing towards water.
Turgor Pressure
• http://www.kscience.co.uk/animations/turgor.htm
• Click on link above for example
The cell’s
vacuole
does not
have any
water in it.
The cell is
flaccid.
The vacuole
does not
have a lot of
water in it.
The vacuole and
cell wall push
against each
other.
The vacuole is
now full of water.