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The Hydroponics Farm: A Design Exploration For Middle School

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 HydrogreenTM 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 52-page chapter of Technology Science Mathematics Connection Activities Binder by James LaPorte and Mark Sanders. New York: Glencoe/McGraw-Hill (ISBN 0-02-636947-8)

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