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Activities: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10
Activity Nine
The Abiotic Limits to Purple Loosestrife Growth
Objectives
The
students will design and conduct a controlled experiment to determine
the effects of an abiotic variable on the growth of purple loosestrife.
State science curriculum objectives
Constructing objectives: 7, 8, 10, 13, 14, 15
Reflecting objectives: 6, 11
Using objectives: OLT
4, EC 3,4,15,16
Methods
Students conduct indoor research on
the effects of soil temperature, water availability, photo period, or
another abiotic variable they believe might have an effect on the growth
of purple loosestrife.
Background
All
plants, including purple loosestrife, survive and thrive where soil,
water, and solar energy amounts are within the limits necessary for
the particular species. Other abiotic factors may also affect the plants
growth. Often plant growth decreases when such factors are very high
and very low. Beyond some level the plant can't grow at all. How do
such abiotic factors effect purple loosestrife? Are there combinations
of these conditions that slow or accelerate growth?
Materials
Two
or more purple loosestrife plants growing in pots according to the directions
given in the activity "Raising Galerucella Beetles Indoors"
(Section 2, page 21). Young plants best.
- Ruler for measuring growth, appropriate lighting,
beaker or liquid measuring container.
- Other materials will vary depending on which
abiotic variable the students choose to test.
- If photo period is being tested, then two timers
on two light sources are needed.
- If soil temperature is tested, then a soil thermometer
is needed.
Procedure
- Start two or more plants growing in pots. (See
directions in activity "Raising Galerucella Beetles Indoors",
Section 2, page 21.)
- Lead discussion with students about what abiotic
conditions are... and what conditions they think might affect the
growth of purple loosestrife. Based on this discussion , students
select which abiotic variable they want to test.
- Students then must alter the growing conditions
for one of the plants so that the variable selected can be tested.
All other conditions must be the same for the two plants (or two groups
of plants). (A) If amount of water is to be tested, then all plants
must be grown in the same soil, the same light routine, the same temperature,
etc. But the amount of water each plant is given needs to be selected
, and that amount carefully measured when it is given. Students need
to determine if they are interested in the amount of water added,
the frequency of water added, or the level of standing water in which
the plants are growing. (B) If photo period is to be tested, then
the control plant and the experimental plants must have separate (but
identical) light sources. Each plant (or group of plants) must be
isolated from other light sources. The light source of the experimental
and controls groups must have timers with different settings so that
one group gets light for a different length of time then the other.
(C)If soil temperature is to be tested, the students must devise some
method to heat or cool the pots of soil, while maintaining all the
other conditions (such as lighting) exactly the same. This might involve
putting the pots inside larger pots in which student maintain ice
or ice water. Or it could involve some sort of heating device like
aquarium heaters or heater "rocks" found in pet shops for
reptiles.
Encourage students to design the experiments
themselves. Make sure they control for all variables except the one
to be tested. Their design should have an experimental group and a
control group. These "groups" may have only one plant in
each, although it would be more scientifically valid if more plants
were used.
- As the plants are grown according to the experimental
plan, observations must be made about the growth and health of the
plants. Growth can be determined by measuring the height of the plant
each day or every other day. Since some extremes of abiotic conditions
actually start to kill the plant, it is also valuable to observe such
things as yellowing of the leaves, wilting, sections of dead tissue,
and dropping of leaves.
- After an appropriate amount of time, compare
the control and experimental plants. [Graphs of height versus time
could be used.] Students decide if the variable made a significant
difference and write a justification for their conclusions.
- Because we don't want to add to the spread
of purple loosestrife, the plants that were grown should be destroyed.
Make sure seeds and live root sections are not introduced into the
outdoor environment.
Extensions
Once the effects of one variable are determined, additional experiments
could be done to determine what combination of conditions slow or accelerate
growth.
The experiment could also be done with several
incremental changes in the variable. For example, one plant could be
grown at room temperature, while other plants are grown 5, 10 and 15
degrees below room temperature.
Ask students to suggest the implications of what
they have learned from their experiment. Can their results explain historical
patterns about where purple loosestrife has and has not appeared in
North America ? Can they suggest an application of this knowledge to
reducing purple loosestrife's impact on a wetland?
Evaluation
Students
are to prepare a written report of their experiment which includes a
statement of their hypothesis, careful description of procedures, all
observations, and a conclusion with clear justification of those conclusions
based on the observations.
Activities: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10
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