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Science, Technology and Environment
Laboratory, Pedagogical Department
P.E., University of Athens, Greece
Gravitropism hands-on device
Sarantos Oikonomidis , Vassilis Grigoriou , Nikos
Kaponikolos , Stavroula Kanavi , George Kalkanis.
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Introduction

• We represent an apparatus with which we can study
  the phenomenon of gravitropism that is the
  attribute of plants to grow against the effective
  gravity.
• We also mention the difficulties and the
  solutions that we came in.
• At last, we propose a didactical approach with
  specific student objectives that our exercise may
  fulfil.

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What is gravitropism?

• Gravitropism is simply a plants response to
  gravity.
• Positive gravitropism When the roots grow with
  gravity.
• Negative gravitropism When shoots grow against
  gravity.
• The research of gravity sensing is very exciting
  right now because the exact mechanism is not
  known.

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Theory

• According to theory, rotating seeds were
  supposed to grow parallel to the resultant of
  their weight and the centripetal force. This
  means that seeds should not grow vertically to
  the ground but to make an angle.

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Variables

• Effective gravity ? Angular velocity
• ? Distance of the flower pot
  from the rotating axle
• dependent
• Other tropism ? Sun
• ? Wind (low angular velocity)
• independent

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The experimental device

• Our device consists of an electric motor which is
  connected with a rubber band to a round metal
  disc. The electric motor is placed in a wooden
  base.
• A piece of steel pipe 1m long, is welded at the
  centre of the metal disc.
• At the other end of the steel pipe, we placed
  vertically an 2m long wooden axle.
• At the wooden axle we put three plates with seeds.

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The experimental device

• Final Assembly

• Axes assembly
• Operation

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The experimental device

• The metal disc rotates with an angular velocity
  of 1rad/s approximately.
• This means that the wooden axis with the seeds
  also rotates with the same velocity.
• As a result, the resultant force at the seed is
  the gravity and the centrifugal force.

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Testing and difficulties

• Selection of seeds.
• Selection of material to deposit seeds.
• Motor selection.
• Transmit motion to axle.
• Select the distance of the flower pot from the
  rotating axle.
• Rotation speed.

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Experimental Results

• Our experimental results comply with our
  expectations. The seeds did not grow vertical to
  the ground, but they formed an angle towards the
  rotation axle.

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Educational proposal

• The experiment should consist of two parts
• One with the aforesaid setup,
• One with the flower pot motionless.
• Thus, it would be feasible to make comparisons
  between the two different ways of grow.

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Student objectives

• This exercise may fulfil a large variety of
  student objectives cognitive and psychomotor.

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Cognitive student objectives

• Students are expected
• To predict the normal response of a seed when
  grown down with gravity.
• To predict the response of a seed when it is
  being rotated.
• To compare the growth patterns of seed that have
  been rotated to those that are growing down with
  gravity.
• To compare the growth and angle of orientation of
  seeds according to angular velocity of the
  device.
• To identify why it is important for a plant to
  have gravity sensing.

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Psychomotor student objectives

• Students are expected
• To explain why it is important to have a control
  for an experiment.
• To measure the growth and change in seed angle
  over time.
• To interpret data generated in tables and graphs.

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Suggestions

• As a future enhancement, we propose an experiment
  where students can study various factors that
  determine seeds grow such as light and
  orientation. With this they will have to handle
  more variables and study the importance of each
  one at the seeds grow.
• The required changes in the experimental setup
  are small, as four electric bulbs are needed and
  a mechanism that turns the vertical axis in
  various angles.