This brief summary gives a glimpse of lessons that might occur
while the model is being developed and maintained.
A hydroponics farm could be an ambitious science activity without
organizing connections to any other classroom. The project described
in these pages is a collaborative effort that crosses three disciplines.
In some schools logistical and bureaucratic problems might create
difficulties for such a project, but this description does not deal
with these problems.
Working on the hydroponics activity, each student may independently
design and explore questions that he or she finds intriguing. Individual
insights will often follow such work. Each student project would
be different from all others. To realize the possibilities of this
activity, the three teachers will need to synchronize content and
to collaborate closely to manage scheduling, subject continuity,
and thematic integrity throughout the project.
Designing and building the model may be the extent of the project,
but the farm can also serve as a laboratory. If investigation is
a goal, the students will need to manipulate a critical variable
while observing the responses of the plants. Early in the design
phase they must determine what variables to study and the model
must be developed so the observation produces comparable results.
They might, for example, choose a factor in the nutrient solution—perhaps
the ratio of materials or pH levels or the amount of light provided
for the seedlings. They will need to understand the concept of the
control group as well as other facets of setting up an experiment.
Science Explorations
In science class, a review of pH may be helpful, since students
will be monitoring their plants' pH levels. If the students need
a refresher on pH, let them use test paper to measure familiar solutions
 tap water, a white vinegar solution, a baking soda solution.
They can then measure the pH of several fertilizer solutions similar
to the plant food that will be used in the model. Compare these
data to the pH preferences of selected vegetables and herbs and
discuss the choices for nutrient solutions that will be most favorable
for the seedlings.
Understanding plant structure, particularly the role of roots
in nourishment, is basic to the design of the hydroponics model.
The students can observe the roots and stems of various plants and
compare similarities and differences. Prepared slides of longitudinal
and transverse cross sections of a root tip will illustrate the
role of individual cells and their functions. A discussion of plant
structures can include such questions as
 How do root hairs serve the plant?
 What factors would make it difficult for a plant's roots to
grow?
 How can the model make use of the plant's natural structure?
Thoughts from Mathematics
In mathematics class students can use their work with the nutrient
solution to expand their understanding of ratios and proportions.
The solutions that provide food for the seedlings are expressed
as ratios. To concoct an appropriate balance that will nourish the
plants, the teams must understand the correct proportions for their
plants' needs. Commercial plant foods provide an analysis of their
ingredients and different formulas are suggested for different plants.
For example, one product, the Hydrogreen^{TM}
Plant Food, provides nitrogen, phosphoric acid, and potash in the
proportion of 10:8:22. The teams can investigate their understanding
of how a ratio reflects the nutrient balance by exploring such questions
as
 What does it mean for the compounds to be in equal proportion?
For example, is there any difference between 1:1:1 and 2:2:2?
 If a mixture has the ratio A:B:C=3:1:4 and you have only 2g
of compound B, what amounts of A and C are needed?
 If the supplies of A, B, and C are 120g, 250g, and 180g, is
it possible to use all the nutrients in the 3:1:4 ratio? If not,
what limitations are present? What is the most nutrient (in grams)
that you could make from these supplies?
The students will be using containers to feed their model's plants,
and will need to predict volume capacity for a variety of containers.
They can explore shapes and containers in mathematics class. Examining
the surface area, dimensions, and volume of prisms, pyramids, cylinders,
and cones will help them understand the relation between shape and
volume. They should think about volume in terms of a container's
height and the area of its base and develop mathematical models
that reflect that relation. After they seem comfortable with their
findings, let them test their mathematical models by predicting
the volume of an irregularly shaped container (such as a soft drink
bottle) and measuring the volume of water needed to fill it (for
water 1 cubic centimeter=1 milliliter).
Issues in Design
During the first stages of design the student teams can examine
possible models for their systems. Most hydroponics farms are either
water cultures (the plant roots are submerged in water) or aggregate
cultures (the roots are surrounded by sand, vermiculite, gravel,
or similar materials).
Every hydroponics design must account for the essentials of plant
biology and the requirements of a delivery system. Students will
also need to think about the physical possibilities in their school
 how much space is available? What is the light source and how
many hours will the plants receive light? What are the temperature
requirements and how can the appropriate temperature be maintained?
The class can use reference materials and explore examples of materials
they will use for construction, such as plastic pipe, tubing, and
aggregate materials. The class can also develop an idea of how the
nutrient will move through the system by observing an aquarium pump
aerate a fish tank. The students can study different examples of
materials and processes used in various hydroponics systems and
then begin to sketch ideas for the design of their model.
The design teams can document their work in a portfolio that includes
such materials as
 information from reference materials
 drawings of possible model designs
 tables that record such data as nutrient solution, nutrient
ratio variations, measurements of plant growth, and hours of light
the plants receive
 notes and personal observations
A detailed guide to this activity in a 52page chapter of Technology
Science Mathematics Connection Activities Binder by James LaPorte
and Mark Sanders. New York: Glencoe/McGrawHill (ISBN 0026369478)
