Did you know that plants can move? They do it all the time, but so slowly that we often don't notice it.
Plants respond to a number of different cues in their environment with movement. These movements
are called tropisms. Some examples of tropisms include gravitropism (response to
gravity), hydrotropism (response to water), thigmotropism (response to touch),
and phototropism (response to light). These tropisms are vital to plants' survival.
In this demonstration, your team will grow three plants. Number one will be the control. It grows
under normal conditions. Plants two and three will be variables of the same type. This means
one variable will be introduced for each of the two remaining plants. The variable will be the
same.
Demonstration: Phototropism
Background:
When a seed germinates, the roots grow downward, and the stem grows upward. If you expose the
growing stems to light from one direction, they start to grow in that direction. In 1809, a Swiss botanist
studied the growth of plants toward a light source and stated that it was caused by an unequal growth
on only one part of the plant. Later, in 1880, Charles Darwin (the father of the theory of evolution),
discovered that it was actually the tips of the sprouting seedlings that were influenced by the direction
of the light source. He discovered that when he covered the tips of growing seedlings, they no longer
responded to the light. When he covered the part of the stem below the tip, but not the tip itself, the
stems responded normally to light. Examine Figure 1, below.
Task: Phototropism
Design a demonstration to prove Darwin correct.
Plant # 1 should grow under normal conditions.
How can you use plants # 2-3 to show that it really is the tip of
the plant that is influenced by a light source such as the sun?
Talk about it and come up with an action plan. Then decide who will
do which task. Things to talk over:
What materials will you use?
Where will you place your growing seedlings?
How will you identify each one?
How long do you think your demonstration will take?
How will you record your results?
Did you know that plants can move? They do it all the time, but so slowly that we often don't notice it.
Plants respond to a number of different cues in their environment with movement. These movements
are called tropisms. Some examples of tropisms include gravitropism (response to
gravity), hydrotropism (response to water), thigmotropism (response to touch),
and phototropism (response to light). These tropisms are vital to plants' survival.
In this demonstration, your team will grow three plants. Number one will be the control. It grows
under normal conditions. Plants two and three will be variables of the same type. This means
one variable will be introduced for each of the two remaining plants. The variable will be the
same.
Demonstration: Gravitropism
Gravitropism (also called geotropism) is the directional growth of an organism in response to gravity.
Roots display positive geotropism when they grow downward, while shoots display negative
geotropism when they grow upward. Among the first scientists to study geotropism was Charles
Darwin, who, along with his son Francis, published The Power of Movement in Plants in 1880.
Despite a long history of studying this subject, there are many questions about how geotropism
actually works.
Task: Gravitropism
Design a demonstration to prove Darwin correct.
Plant # 1 should grow under normal conditions.
How can you use plants # 2-3 to show that plant roots grow with
gravity while their stems grow against gravity?
Talk about it and come up with an action plan. Then decide who will
do which task. Things to talk over:
What materials will you use?
Where will you place your growing seedlings?
How will you identify each one?
How long do you think your demonstration will take?
How will you record your results?
Did you know that plants can move? They do it all the time, but so slowly that we often don't notice it.
Plants respond to a number of different cues in their environment with movement. These movements
are called tropisms. Some examples of tropisms include gravitropism (response to
gravity), hydrotropism (response to water), thigmotropism (response to touch),
and phototropism (response to light). These tropisms are vital to plants' survival.
In this demonstration, your team will grow three plants. Number one will be the control. It grows
under normal conditions. Plants two and three will be variables of the same type. This means
one variable will be introduced for each of the two remaining plants. The variable will be the
same.
Demonstration: Hydrotropism
Hydrotropism describes a plant’s tendency to grow toward a water source. One of the reasons that
plants grow downward is because they are seeking water.
Task: Hydrotropism
Design a demonstration to show hydrotropism.
Plant # 1 should grow under normal conditions.
How can you use plants # 2-3 to show that plant roots grow with
gravity while their stems grow against gravity?
Talk about it and come up with an action plan. Then decide who will
do which task. Things to talk over:
What materials will you use?
Where will you place your growing seedlings?
How will you identify each one?
How long do you think your demonstration will take?
How will you record your results?
Independent Student Response
Why do we only change one variable at a time?
What is a control?
Draw and image of your experiment. Write your hypothesis in a complete
sentence.
Hypothesis: