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Forces and Responses
How do living things respond to
forces?
• TEKS 7.7C Demonstrate and illustrate forces
that affect motion in everyday life, such as
emergence of seedlings, turgor pressure, and
geotropism
• TEKS 7.13A Investigate how organisms
respond to external stimuli found in the
environment such as phototropism and fight
or flight
Forces
• A Force is a push or a pull on an object in a
specific direction
Forces can be used by living organisms to
perform basic functions.
Forces are used in many ways by
humans.
For example, interactions between the muscular & skeletal systems allow the
body to apply forces needed for movement.
Humans use the force of their heart muscles
contracting to keep blood flowing through their bodies.
The roots of plants use force to push through
the soil.
• Plants use force in other ways by changing
their growth in response to their environment.
The way a plant responds to stimuli is
called a tropism.
Geotropism
• Geotropism occurs when a plant grows or
bends in response to gravity.
A plant’s shoots will grow up and its
roots will grow down.
Phototropism
• The way a plant grows or bends in response to
light is called phototropism.
The plant will grow toward light, even if it must
grow sideways.
When a plant takes in water, the vacuole fills up and
exerts pressure on the plant’s cell wall.
This pressure is called turgor pressure.
Turgor pressure allows a plant to become rigid
causing the plant to stand upright.